Summary

• Fish stocking[1] is the practice of raising fish in hatcheries and releasing them into rivers, lakes, or the ocean.
• 35-150 billion finfish are stocked every year.
• Fish are stocked to:
• increase the catch in commercial fisheries (probably tens of billions of stocked fish annually),
• increase the catch in recreational/sport fisheries (billions of stocked fish annually),
• restore a population of threatened or endangered species (the number of stocked fish seems to be lower)
• Fish can be stocked when they are anywhere between the egg stage and multiple years old. The mean time spent in hatcheries/farms seems to be somewhere between 8 days and 4 months. Fish stocked to enhance recreational fisheries tend to be released when they are older than those stocked to enhance commercial fisheries.
• Usually, fish are stocked to maximize economic outputs so we shouldn’t expect fish welfare to be given sufficient consideration. It’s unclear how much hatcheries are incentivized to breed healthy and unstressed fish that would have higher survivorship after the release. Bigger fish may also starve and suffer after their release due to their lack of survival skills.
• I was unable to find any animal advocacy organization that is working on reducing the suffering caused by fish stocking. I found very few articles that talk about fish stocking from an animal welfare perspective.[2]
• Possible interventions include lobbying to decrease the number of fish stocked for recreational fishers and requiring better conditions in hatcheries. I am very uncertain if such interventions would be cost-effective compared to ACE’s recommended charities.
• Fish stocking has various ecological effects (e.g., a decrease in the genetic diversity of wild populations) that would need to be well-understood before seriously considering trying to reduce the number of stocked fish.

Context

This article is a part of a series of articles by Rethink Priorities about animals farmed for various purposes. We chose to write about this topic because it seems fairly important and it’s possible that animal advocates haven’t addressed welfare problems related to fish stocking simply because they didn’t know about them.

Charity Entrepreneurship (CE) has recently released a report that considered the advantages and disadvantages of founding a charity that tackles problems related to fish stocking and baitfish. The report used my preliminary research on fish stocking, but it was written before I wrote most of this article. CE’s report provisionally concluded that interventions in these areas are only “somewhat promising” compared to other interventions they considered. I disagree with some aspects[3] of their report, but I have no opinion on whether the conclusion is correct. In general, I think that more in-depth research would be needed to determine whether this is a problem that should eventually be tackled by animal activists. I am uncertain if such research should currently be a priority.

The number of fish stocked annually worldwide

I haven’t found any estimates of the number of fish stocked worldwide, but I found estimates for various countries and regions:

• China: A 2006 programme planned to release 20 billion juvenile fish annually and to increase it to 40 billion by 2020. China’s 2011-2015 Fisheries Plan includes releasing 150 billion juvenile fish (which is 30 billion per year)[4] and claims that 109 billion young fish were released since a previous five-year plan was made in 2006.[5] It should be noted that these statistics are from China’s government and some doubt whether China’s government is a reliable source. For example, China has probably over-reported the catch from wild fisheries in the 1990s.
• EU: Cooke and Cowx (2006) cites Cowx and Godkin’s (2000) estimate that “some 40 billion individuals are stocked annually in European fresh waters”. I could not access Cowx and Godkin (2000), but its summary contains the following text:

Information on quantities of fish stocked was difficult to access. Salmon probably represents the species that has received the greatest attention, with an estimated 20 billion individuals, of various juvenile life stages, mainly eggs and fry, were stocked in 1998. High levels of stocking were also recorded for rainbow trout, coregonids, whitefish, eel, common carp and various cyprinids to support recreational and commercial inland fisheries.

Note that this data is from over 20 years ago, and I was unable to find other authors that make similar claims. Furthermore, it includes stocked eggs. According to Figure 2 of Cowx (2002), out of the ~20 billion Atlantic salmon stocked in the EU in 1998, less than 4 billion were eggs, and the rest were hatched juveniles.

• Germany: Arlinghaus, et al. (2015) claims that in Germany around 77 million fish were stocked in 2010 by anglers in clubs. Note that more fish may have been stocked by other groups in Germany.
• Russia: NPAFC (2019) claims that Russia releases around 1 billion salmon every year. Chebanov and Billard (2001) claim that at the time of writing the article, Russia was producing 100 million sturgeon juveniles per year. Dickinson (2018) mentions that currently Russia is “releasing 50 million or more sturgeon raised in hatcheries.” Vorotnikov (2019) claims that a new hatchery “is designed to produce five million sterlet fingerlings and one million trout (Salmo gairdneri) fingerlings per year at full capacity.” Russia may be stocking other species as well.
• U.S.: According to aquaculture censuses, the number of fish stocked in the U.S. was over 2.9 billion in 2005, and over 3.6 billion in 2013.[6]
• Canada: NPAFC (2019) claims that in 2017 Canada released 368 million salmon. There also seems to be significant stocking in inland waters for recreational fishers. For example, Ontario’s Community Hatchery Program claims that community hatcheries it supported released 6.7 million fish in 2017.
• Japan: NPAFC (2019) claims that Japan is stocking ~1.8 billion salmon to every year. Also, according to Koichi, et al. (2015), in 2011, Japan released around 15 million flounders, 12 million red seabreams, and lesser numbers of other finfish.[7]
• Thailand: Jutagate and Rattanachai (2010) claim that 2.5 billion fish and giant water prawn were stocked into inland waters in 2009 and 1.95 billion fish were stocked in 2008. However, numbers in an accompanying table are much lower which makes me uncertain if these totals are correct.
• Myanmar: According to the table 3 in Oo (2010), 740.6 million seed were produced for stock enhancement by finfish hatcheries in 2008-2009. It seems that the word seed here refers to hatched fish.
• Iran: Brown and Day (2002) claims that in 1996, Iran released over 250 million fish.
• Caspian sea: Vorotnikov (2018) claims that Azerbaijan and Kazakhstan are releasing about 20 million sturgeon fingerlings per year into the Caspian sea and that this number is expected to increase.
• The rest of the world: Leber (2012) claims that “marine fisheries enhancement is happening around the world and in some countries on a massive scale (e.g., China).” After claiming that “some 40 billion individuals are stocked annually in European fresh waters”, Cooke and Cowx (2006) state that “stocking to a similar scale is common across the world.” I don’t think that there are other regions that stock at the same scale as China and possibly Europe, but it does seem that almost all countries do at least some stocking. FAO page Stocking techniques for increased production claims that:

Stocking is widespread in Latin America where the greatest development has been achieved in Cuba, Mexico and parts of Brazil. [...] As regards Asia, successful stocking programmes are reported from India and China. Variable results are reported from Southeast Asia where it has been possible to raise catch levels from 20 to 100 kg/ha in some waters in Thailand, Indonesia, the Philippines and Malaysia. Data for Africa are rather scarce although this continent has fisheries that are supported by stocking.

The FAO article also claims “[n]inety-four countries have reported stocking to FAO as part of their fishery statistics”, but I haven’t found these statistics on the FAO’s website.

To estimate how many fish are stocked worldwide annually, I created a Guesstimate model in which I used subjective 90% confidence intervals to reflect the uncertainty about the numbers above and guessed how many fish are stocked in regions for which I didn’t find any statistics. I guessed that numbers of fish stocked per capita in countries that I haven’t found the statistics for are lower that the ones above.[8] According to the model, 35-150 billion fish are stocked every year. The estimate excludes:

• Stocked eggs. The stocking of eggs doesn’t lead to the same welfare concerns as the stocking of juveniles. In some cases, it wasn’t clear whether the numbers in figures cited above included stocked eggs. Consequently, I lowered the lower bounds of the 90% confidence intervals in my Guesstimate model for some regions.
• Shellfish. I focused on finfish to avoid the uncertainty about shellfish sentience. However, shellfish are also stocked in big numbers. According to Koichi et al. (2015), in 2011, Japan stocked over 10 billion Manila clams, and 3 billion scallop spats, hundreds of millions of kuruma prawns, and tens of millions of crabs. According to the U.S. Aquaculture Census, in 2013 U.S. stocked 1.25 billion eggs or seed stock of clams, and 1.59 billion eggs or seed stock of oysters. I am uncertain about whether all shellfish stocking is done in the form of eggs, and what is the scale of shellfish stocking in other countries.
• Illegal stocking. According to Johnson (2011), illegal stocking is a global problem. The article seems to assume that in North America fish are stocked illegally for the benefit of recreational fishers. According to the article, the main problem is that such stocking subjects “the entire fishery and ecosystem to a degree of unnecessary risk from diseases, parasites, and invasive species that could have been accidentally introduced with the stocked fishes.” Furthermore, “some angler introductions have turned into tremendously expensive cleanup projects.” I haven’t seen any estimates of the number of illegally stocked fish. My intuition is that they are a small percentage of all stocked fish.[9]
• Fish deaths in hatcheries before the stocking. FRS (2003) claim that for salmon and trout, “[s]molt rearing hatcheries can have a 90% survival rate compared with less than 1% in the wild.” Similarly, Araki et al. (2008) cite Reisenbichler et al. (2004) to claim that for salmon “survival from egg to smolt is usually 85–95% in hatcheries versus 1–5% in the wild.”[10] I haven’t found survival rates for other species. Also note that there are occasional mass die-off events in hatcheries, which may not be included in such mortality estimates.
• Translocated fish. Ingram and Silva (2015) claims that:

Most stocking programs have required, and usually preceded by, the development of hatchery and nursery production techniques for the target species, though some stockings may involve the capture of juveniles/seedstock in one area, where recruitment is healthy, and translocation to another area where recruitment is inadequate or lacking.

I was unable to find any statistics on what percentage of stocked fish are translocated rather than raised in hatcheries. Some sources for the numbers of stocked fish (e.g. NPAFC (2019), the U.S. Aquaculture Census, Oo (2010)) explicitly say that the fish were produced in hatcheries. In other cases it was unclear whether given statistics include translocated fish. I guessed that between 0.1% and 20% of stocked fish that are included in numbers cited above were translocated, and subtracted them from the total in the Guesstimate model. My guessed percentage is low because some of the articles I read assumed that all fish were in hatcheries. The few articles that did mention translocated fish also mentioned that it is not the most common practice (like in the quote above).

The number of stocked fish (35-150 billion) is comparable with an estimated 75 billion farmed land animals (FAO[11], 2017 data), and 48-160 billion farmed fish that are slaughtered for meat every year. However, fish farmed for food generally stay in farms longer than fish raised for stocking. Many stocked fish are released when they are less than five days old. Furthermore, it seems that many more fish juveniles are raised to be stocked in aquaculture systems (see the appendix).

Trends

Ingram and Silva (2015) claims that:

Stocking hatchery-produced fish is seen as a means of meeting the demands for seafood products and to meet the need for food security in an increasingly populated world. Stocking as a means of providing a food resource will be a priority for future aquaculture.

Figure 6 in Shen and Heino (2013) report that the number of fish used in marine stock enhancement by China has increased from around 2 billion in 2001 to 13 billion in 2010. Note that this excludes stocking for inland waters.

Figure 5 in NPAFC (2019) indicates that the combined number of salmon stocked by the U.S., Japan, Russia, and Canada has remained fairly stable at 5 billion per year over the last 30 years.

Table 2 in Halverson (2008) provides some statistics about the total number and weight of fish stocked by the U.S. federal government and the 33 states for which data was available for all represented years. The statistics are summarised in the graph below. The graph suggests that the number of fish stocked was much higher in the 1930s, but has been relatively stable between 1958 and 2004. The total weight of stocked fish seems to have been increasing between 1936 and 2004.

According to the aquaculture censuses, the number of fish stocked in the U.S. was 3.4 billion (147 million kilograms) in 1998, 2.9 billion (28.8 million kilograms) in 2005, and over 3.6 billion (42.6 million kilograms) in 2013. This suggests that the average weight of stocked fish (and the mean amount of time fish spend in hatcheries) can be very different in different years. We will have more information about the current situation when the 2018 U.S. aquaculture census is released. Figure 10 in Stopha (2018) suggests that Alaska’s salmon releases have remained relatively stable at ~1.6 billion.

Note that the data from Halverson (2008) only includes data from 33 states and seems to exclude most of the stocked salmon. Consequently, its figures cannot be compared to the U.S. census, which is why I did not include the data from the censuses to the graph above.

Overall, I think that the number of fish stocked worldwide is more likely to be increasing than decreasing, but I am uncertain.

Purposes of stocking

Ingram and Silva (2015) claims that:

The primary purposes of stocking in developed countries is for recovery of threatened species and to support recreational fishing, whereas in developing countries it is more to increase food fish supplies for rural communities and improve their livelihood through income from fish harvested.

Similarly, FAO page Stocking techniques for increased production claims that

Stocks of coregonids, perch and zander are maintained in many alpine and northern European lakes in support of commercial as well as recreational fisheries. [...] Stocking programmes are also widely used throughout the USA and Canada where the emphasis is on management for balanced populations for recreational fisheries. [...] In general, stocking programmes aim at supporting commercial fisheries. In Brazil, stocking was a statutory requirement for mitigation of effects of dams.

Braithwaite and Salvanes (2010) claim that stocking is also sometimes used “to counter the detrimental effects of anthropogenic disruptions, such as dam building, river straightening or effluent pollution that are believed to have contributed to high levels of mortality in natural populations.”

This graph from Ingram and Silva (2015) suggests that in 1999 in Asia and Oceania most stocking programs (~60) were implemented for the purpose of “food & income”, but there were also some programs that stocked for recreation (~13), biomanipulation (~8), conservation (~6), mitigation (2), or restoration (1) purposes.

The purpose of a 2006 programme in China that (amongst other actions) planned to release 20-40 billion juvenile fish annually was to “reverse the trend of deterioration of the aquatic environment, decline of fisheries resources and the increasing number of endangered species, reduce overcapacity, and improve the efficiency of fishing operation and economic benefits.” Developing recreational fisheries is mentioned amongst the reasons for the program, but it doesn’t seem to be the main goal.

According to Table 2 in Halverson (2008), in 2004 out of 1.75 billion fish stocked in the U.S., 1.43 billion were sport fish (stocked for the benefit of recreational fishers), 292 million were salmon and steelhead (purpose not specified), and 24 million were “rare and declining” fish, probably stocked for conservation/restoration purposes. This suggests that stocking for conservation is small in scale, at least in the U.S. However, the article mentions that some fish stockings could be put in several categories.

Note that Halverson (2008) doesn’t include most of the ~1.9 billion salmon stocked by the U.S. every year, of which ~1.6 billion is stocked by Alaska. According to the figure 12 in Stopha (2018), in 2017, 73% of Alaska salmon hatchery production was harvested in the common property commercial fisheries, 19% was cost-recovery commercial harvest (which funds hatchery operations), 8% was "[o]ther (broodstock, etc.)", and <1% was sport, personal use, and subsistence harvests. Morita et al. (2006) assumes that the majority of salmon stocked in Hokkaido Island (where ~1.2 billion salmon are released annually) is caught by commercial fisherman, but also mentions significant catches by recreational fishers. Overall, it seems that most of the salmon is stocked for commercial fishers though there are also significant numbers stocked for recreational fishers.

In general, my impression is that tens of billions of the fish are stocked to enhance commercial fisheries, billions of fish are stocked to enhance recreational fisheries, and the number of fish stocked for other purposes is lower. However, I am uncertain. It could be that a bigger proportion is stocked for recreational fishers or conservation.

Time spent in hatcheries

Welcomme and Bartley (1998) claim that:

Migratory and anadromous fish such as salmonids are usually stocked at a small stage (fry) to acclimate to the natal river and to prepare for migration as their size increases. Cyprinids on the other hand are generally stocked at a larger stage (fingerlings). Recreational fisheries increasingly tend to rely on even larger fish of cacheable size and to rely less on grow-out in the natural environment, although behaviour considerations may limit the upper size at which fish can be stocked due to conditioning in the hatchery environment.

Many other sources also use words like fry and fingerling to describe the age of stocked fish. However, not all sources use these words consistently and the age of the fish it refers to depends on the species. In general, it seems that fry can be anywhere between 2 days to a couple of months old,[12] while fingerlings are older than 3 weeks but younger than one year.[13]

Wikipedia uses these images to illustrate what fry and fingerling look like.

According to the U.S. Aquaculture Census, in 2013 U.S. stocked:

• 2.5 billion salmon (mean weight is 3.2 grams)
• 719 million walleye (0.6 grams)
• 177 million trout (89 grams)
• 8.5 million catfish (250 grams)
• 168 million other fish (3 grams)

The stats above suggest that the mean weight at release can be very different for different species, which suggests that the mean age at release can depend a lot on species as well. Note that these stats exclude eggs and that a more detailed (but older and less complete) breakdown of fish stocked in the U.S. and their total weights can be found in Halverson (2008).

There is also a variance based on location. For example, Monacelli (2015) claims that in 2015 in New Jersey it was planned to stock nearly 600,000 trout of which the vast majority[14] would be 18 months old, 10.5 inches (27 cm) and about half a pound (227 grams). That is significantly higher than the 89 grams average for trout in the U.S.[15] Table 1c in Munro and Wallace (2018) show that in Scotland steelhead trout over 900 grams are produced for stocking.

Such variance makes it very difficult to understand what is the mean age at stocking of all fish. Furthermore, fish that are stocked for recreational fishers receive more attention, especially if they are bigger, which leads to unrepresentative web search results. Nevertheless, I summarise my findings on the age and size of stocked fish below.

According to NPAFC (2019), about 90%[16] of the salmon stocked by Canada, Japan, Korea, Russia, and the U.S. are pink and chum salmon. Stopha (2018) claims that “pink and chum salmon are the most economical to raise because fry can migrate to saltwater soon after hatching.” Kitada (2014) claims that chum salmon remain in hatcheries (from eggs to release) for about 6 months. Less commonly stocked salmon and trout species seem to stay in hatcheries longer. Tatara et al. (2017) and Salminen et al. (2007) discuss releasing steelhead and Atlantic salmon when they are two years old versus one-year-old. However, not all stocked salmon are raised until this age. According to Figure 2 of Cowx (2002), in 1998 EU countries stocked almost ~4 billion salmon eggs, 14 billion salmon fry, and ~0.4 billion older salmon (parr or smolts). Similarly, Morita et al. (2006) cite Miyakoshi (2004) to claim that during 1993-2000 in Hokkaido Island, Japan, 60-70% of released masu salmon juveniles were fry and 10-20% were smolts (1-year-olds), but I was unable to confirm it in the cited article. Also, masu salmon is only a small percentage of the ~1.2 billion salmon stocked annually by the island. Welcomme and Bartley (1998) also mention that most salmon are stocked when they are fry. Salmon stocked for recreational fishers seem to be stocked when they are older, but they seem to be fewer in numbers.

De Silva (2010) claims that in China, “strict guidelines are adhered to on the size of seed for stocking, often around 15 cm in body length.” This suggests that China stocks relatively mature fish. However, it’s very unclear to what proportion of fish stocked by China this applies.

Jutagate and Kwangkhang (2015) claim that giant freshwater prawn “is normally released as 30 day old post larvae”, although in some countries they are stocked when they are 45-90 days old.

Recreational

As I understand it, all of the following sources in this section talk about fish stocked mostly for the benefit of recreational anglers, although in some cases ecological reasons are also mentioned.

Enger (2014) claims that 350 million small fish are stocked into Minnesota's lakes every year. It also states that “the vast majority of those are walleye fry, two- or three-day-old fish.” This video also shows that walleye are stocked soon after hatching.

According to figure 2 in Halverson (2008), around 57% of fish stocked in the U.S. in 2004 (excluding most of the salmon) were large (> 15.2 cm), ~36% were fingerlings (2.5 to 15.2 cm), and ~7% were fry (<2.5 cm).

Janonis (2014) claims that most of the fish stocked in Lithuania are one year old, or 3-4 months old. The article also claims that 18-19 million fish were stocked in Lithuania in 2014, but at least 10 million of them were eggs.

Arlinghaus et al. (2015) claim that in Germany around 77 million fish were stocked in 2010 by anglers in clubs and that in total they weighed about 3,691 tons. That means that the average weight of a fish was around 48 grams which suggests that many of them spent considerable time in hatcheries.

It seems that most of the trout are stocked when they are over one year old:

• New York State’s 2017 and 2019 stocking plans show that over 80% of the 3 million trout and salmon stocked in Lake Ontario in both years were yearlings, and the rest are fingerlings. (Yearling is generally defined as “an animal that is one year old or has not completed its second year.”)
• Out of 1.2 million salmonid (mostly trout) reportedly released in Victoria, Australia in 2017, 30% were “Fry up to 20gm”, 62.1% were “Yearlings - 20g to 150g”, 7.7% were “Advanced Yearling 150gm+”, and 0.2% were “Ex Brood Stock 1kg+”.
• Using the information in the appendixes of Kerr (2006), I calculated that out of 8.9 million fish stocked in Ontario in 2004, 0.8% were eyed eggs, 1.7% were fry, 16.8% were fingerlings, 79.5% were yearlings, 1.4% were subadults, and 0.1% were adults. Most of the stocked fish were trout.
• Kitada (2014) claims that steelhead trout remain in hatcheries for about a year.

Most trout seem to be stocked when they are over a year old

Welfare concerns

I don’t have the expertise required to review fish welfare in depth. Superficially, videos of U.S. sport fish hatcheries suggest that conditions are not good.[17] In many cases, fish seem to be overcrowded, and no environmental enrichment can be seen. Furthermore, many of the fish stocked in California, Alaska, British Columbia, and probably many other places are triploid (with three complete sets of chromosomes instead of the typical two) to protect the genetic integrity of wild fish populations. According to Greig (2019), all these factors can be bad for fish welfare. We also see in videos that there are multiple changes in the environment in hatcheries that may cause fish stress, especially during the transportation and stocking. Some fish are transported in backpacks or thrown to lakes from airplanes and helicopters. Urness (2017) mentions that about 95% of trout fingerlings survive the fall from a helicopter. It’s also possible that many fish are injured by the fall. What is more, according to Brown and Day (2002), “there is a large body of evidence showing that transportation has a significant effect on the stress levels of hatchery fish.” Finally, there is suffering involved in the collection of eggs (e.g., see this video), although it has to be endured by relatively few individuals.

Note that the concerns above may only apply to fish grown in particular countries or for a particular purpose. Conditions in other hatcheries could be very different. However, almost all of these systems are designed to maximize economic outputs. Judging from the conditions for animals farmed for food, we should expect animal welfare to be compromised whenever it is in conflict with economic incentives.

It’s possible that the welfare of stocked fish is aligned with economic incentives more than the welfare of food animals. The healthier fish are at the time of stocking, the more likely they are to survive in the wild and eventually get caught. Wootten (1998) claims:

The treatment of stocked fish once released is extremely difficult because of the volume of water involved. [...] It follows then, that it will be especially advantageous to ensure that the health status of fish is as high as possible before they are stocked. [...] It is in any case important to use fish of as high a quality as possible, preferably from known, reputable sources. [...]. They must not be overcrowded or exposed to excessively high temperatures. Badly-transported and thus highly stressed fish will be very vulnerable to outbreaks of disease.

On the other hand, incentives of hatcheries may not always be so straightforward. Brown and Day (2002) claim:

Conservation biology has long emphasized the importance of practices such as environmental enrichment, pre-release training programmes and soft release to improve the post-release survivorship of captive-bred animals. In contrast, the production of ecologically viable individuals is not part of the hatchery equation because the production of large quantities of fish, rather than natural history, behaviour and ecology, largely guides hatchery practices. Agersborg (1934) states that rapid growth and high survivorship within the hatchery have been the fundamentals of aquaculture for years. This position still reigns supreme today. Many hatcheries are government funded or at least heavily subsidized. The level of success, and hence funding is often being determined by the number of fish released rather than by the survival rates of those fish or the return to anglers and the industry.

If that is still true today, we should expect there to be more problems with fish health in hatcheries as well. Furthermore, Brown and Day (2002) also describe how behavioral deficits result in poor survival rates (commonly 1-5%[18]) and suffering after the release:

Following release many captive-reared fish may not eat at all for several days, weeks or up to a month. When they do start to forage, they typically take up high risk and energetically costly positions[...] As a result hatchery-reared fish show substantial weight loss compared to transplanted wild fish and their mortality rates can be up to 10 times greater than that of wild fish.

[...]

Fish reared in captivity are completely predator naïve because they are provided with no opportunity to interact with predators prior to release. Predation is thought to be the principal cause of mortality among released hatchery fish

Comparison with fish farming

Lymbery (2002) suggests that releasing fish to grow in their natural environment and recapturing them when they are mature (sea ranching) could be better for fish welfare than growing fish in farms for all their lives. The report calls it “free range farming.” It states that it has a potential for high welfare but “it brings with it natural threats such as increased predation and food shortage.” I think that the comparison between the two systems is more complicated. Since the mortality of stocked fish after the release is much higher than in farms, more fish have to be raised in hatcheries for the same amount of meat. Better data on mortality rates, age at release, and size at slaughter would be needed to calculate whether farmed fish require less or more time spent in hatcheries/farms than stocked fish for the same amount of meat. It should also be noted that stocked fish only live in hatcheries when they are young. I am not sure if there are reasons to think that young fish are less morally relevant than adults. However, stocked fish may also suffer after the release, including possibly cruel deaths. Finally, the two systems have different ecological effects, which could be the most important factor.

Ecological effects

Ingram and Silva (2015) claim that fish stocking can also have negative effects on wild populations, including:

• A possible loss of genetic diversity.
• Transmission or introduction of infectious diseases and pathogens.
• Releasing chemicals that are commonly used in aquaculture facilities.
• Non-endemic stocked fish may out-compete, displace or prey on native endemic species altering food web and community structure (e.g., see MacDonald (2018)).

Cooke and Cowx (2006) state that fish stocking is recognized as a global environmental degradation problem. Young et al. (2014) summarises a scientific consensus on salmon stocking. It claims that stocking may increase the number of adults temporarily, but is likely to reduce the longer-term productivity of a population, partly due to loss of genetic integrity.

It should also be noted that many of the stocked fish are predators. Not only does this mean that they prey on other fish, worms, and insects when released, but also that in hatcheries they are fed diets that include fish, poultry and other animal products, just like fish farmed for food.[19] Fishcount.org.uk estimated that roughly 440-1,200 billion wild fish were used as aquaculture feeds in the late 2000s and this number has probably increased since due to the fast growth of aquaculture. Even though aquaculture of stocked fish is probably only responsible for a small fraction of this number, it may still affect many individuals.

There are probably many other effects of fish stocking, some of which are normally considered to be positive and hence are less discussed within the literature. Before seriously considering reducing the number of stocked fish, it’s vital to understand how fish stocking affects wild animal welfare as this could be the most important factor. However, this is a complex topic that is beyond the scope of this article.

Who are the decision makers?

If we want to influence fish stocking decisions, we will need to know the decision makers. Ingram and Silva (2015) summarises the situation:

A wide range of stakeholders are involved in stocking programs, both directly and indirectly, and include decision-makers at all levels from village leaders to country agencies, fisheries, aquaculture, water, environmental and conservation managers, water agencies and end users (e.g. commercial and recreational fishers, fishmongers and consumers). Waterways and water bodies that are stocked may be managed by agencies for the state as common pool (non-private ownership), or be owned by individuals, communities or corporate bodies. [...] Often, particularly in developed countries, stocking activities are governed by various policies, regulations and legislation, to ensure that stocking is conducted in a responsible an ecologically sustainable manner. Stocking of public waters tends to be more heavily regulated by authorities [...] In contrast, stocking of private waters (on private land) tends to be less regulated.

Halverson (2008) claims that in the U.S. most of the stocking was done by state agencies and that some stocking was also done by the U.S. Fish and Wildlife Service. It also claims that managers have made substantial changes in their approach to fish stocking in response to criticism and debate about the ecological impact. It cites Jackson et al. (2004) which concluded from a survey of fisheries managers that “public pressure to stock cultured fishes is an important influence on agency decisions to use cultured fishes.” This suggests that public pressure could maybe be used to mitigate welfare concerns as well. It should also be noted that agencies sometimes consult with the angling public to decide how to stock waters.

Simcock (2017) claims that “in Alaska, large-scale salmon enhancements are run by community-based Aquaculture Associations.” Decisions about the number of stocked fish seem to be at least partially made by the Alaska Board of Fisheries which sometimes calls the public for proposals. Smoker and Heard (2007) mentions that some hatcheries in Alaska release over 100 million juvenile salmon annually. This shows that a large number of individuals could be helped by influencing a single hatchery.

Silva et al. (2015) claim that in Thailand stocking is implemented by many agencies such as Department of Fisheries, Tambon (Local) Administration Organization, provincial agencies, Electricity Generating Authority of Thailand and other private sector and government agencies. The article also claims that in 2013, the Department of Fisheries stocked 1.3 billion fingerlings which seems to be the majority of fish stocked in Thailand.

Possible interventions

Recreational fishing

Reducing the number of fish stocked for recreational fishing would decrease the number of:

• fish that are being raised hatcheries,
• fish that starve and struggle to survive after stocking,
• fish that have to endure being caught by fishers (many of which are then released injured, most of the others die without a humane slaughter),
• worms, fish, and other animals used as a live bait

All of these effects seem to be positive. However, it would also have various ecological effects, which would need to be well-understood before taking action because they could be more important than the effects listed above. Also, I think it would be important to make it clear that we are not against stocking for conservation as such a position would probably be much more controversial.

The number of stocked sport fish could maybe be reduced by lobbying relevant agencies. Or perhaps the prohibition of stocking for recreational fishers could be achieved by ballot initiatives.[20] Maybe the prohibition could be added to some propositions that are primarily about improving conditions for farmed food animals (perhaps together with prohibitions of other cruel practices like farming fish to be used as live bait and selling pet snakes). I imagine that many voters wouldn’t like that the taxpayer money is spent to stock fish for recreational anglers, especially if many of them die instead of being caught. Furthermore, contrary to welfare reforms, such campaigning for prohibitions can be compatible with a more rights-based perspective of animals (see Francione (2007)), which could allow animal activists to campaign as more of a united front or at least to avoid infighting.[21]

Another option is trying to reduce the demand for sport fish stocking by decreasing the popularity of recreational fishing. It may be difficult to change people’s behavior directly, but perhaps angling regulations could be made more restrictive. Note that stocking is just one of many potentially negative effects of recreational fishing, as billions[22] of fish are caught by anglers worldwide, and countless animals are used as live bait. Furthermore, arguing against humans getting pleasure from directly killing or injuring animals could help to expand society’s moral circle. Finally, restrictions on angling could be easier to influence than restrictions on food producers who have powerful lobbies.

It could be that it’s easier to prevent the emergence of new recreational fisheries rather than reducing the scale of existing ones. According to Funge-Smith et al. (2018), fishing license sales have been declining in countries like the U.S. and France, but “[t]here is evidence that recreational fisheries are growing strongly in emerging economies.” If this is true, preventing the development of sport fisheries and sport fish stocking in emerging economies could be more promising than targeting developed countries.

Commercial fishing

Lorenzen (2014) claims that “[m]any enhancements fail to meet their objectives and some do considerable ecological or genetic harm, yet such enhancements often persist.” This suggests that the number of fish stocked could maybe be reduced by arguing to stop ineffective and ecologically harmful programs. However, I’m uncertain whether stocking fishes to enhance commercial fisheries is bad from the animal welfare perspective. If fish were not stocked, that would still likely result in less ‘wild’ fish being caught. It’s possible that there would be an increase in fish farming to compensate for the loss, as this is how decreasing catches are already increasingly compensated. It’s unclear which of these systems involves more suffering.

Brown and Day (2002) suggests requiring higher survival rates of stocked fish and suggests ways to do it. It would also likely increase the cost per fish and lead to fewer individuals being needed to achieve similar effects for fisheries. This could be good because fewer fish would need to endure being raised in hatcheries, and there could be less suffering after the release due to lack of survival skills. However, Brown and Day (2002) also claim that this could make fish stocking more efficient. It’s unclear whether that would be better for animals in the long run because it could make stocking more popular.

Also note that when considering interventions in this space, it’s also important to take into account the effect on people who depend on fishing and fish stocking as the source of livelihood or food.

Improving conditions in hatcheries

The Open Philanthropy Project has recently recommended several grants to improve conditions of farmed fish. Perhaps improving the conditions of fish raised for stocking is also an option. However, it would be different campaigns because decision makers are different. Furthermore, it could be harder for the general public to understand the ask. Requiring better conditions in hatcheries may also decrease the number of fish stocked, and we may still have to make sure that it would be good for animals.

Overall, I am very uncertain whether this or other interventions I suggested could be cost-effective.

Questions for further research

I am uncertain if more research on this topic should currently be a priority. However, if such research was done, these are the topics that I think are the most important:

• What are the most promising interventions? In which countries could they be implemented? How cost-effective could they be compared to other animal welfare interventions? If they could be effective, what should be the next steps? I think that researching these practical questions is of the highest priority.
• How does fish stocking impact wild animal welfare? It’s clear that fish stocking has significant ecological impacts. There seems to be quite a lot of literature about its effects on the health of ecosystems and how it may be causing environmental degradation, but I haven’t seen any discussion about the effects on wild animal welfare.
• Would reducing the number of stocked fish reduce the overall amount of animal suffering? Note that the answer may be different for different species, countries, and purposes of fish stocking.
• What are the biggest sources of suffering for stocked fish? Are there cheap ways to reduce suffering? It should be taken into account that suffering can happen both in hatcheries, and after the release.
• How much time do fish spend in hatcheries? I was surprised by how little information I was able to find about it. Since people who work in fish stocking may know the answers, maybe some information could be gained by simply asking them.
• Are juvenile fish less sentient and morally relevant than adult fish? When do fish become sentient? For example, Birch (2018) argues that zebrafish may already be sentient at five days post fertilization because they seem to respond to noxious stimuli the same way adults do. More evidence like this could help to see how important are conditions in hatcheries during the early stages of fish development.

Note that I (and Rethink Priorities in general) currently have no plans to research any of these questions.

Appendix: huge numbers of juveniles raised for an unknown reason

During my research for this article, I encountered some surprisingly high numbers of juveniles that are raised in hatcheries, seemingly to be farmed for food. Hishamunda and Subasinghe (2003) provide the following statistics about China’s aquaculture:

In 2000, it took about 2.56 million tonnes of fingerlings to stock freshwater aquaculture systems. These were produced from 602.2 billion fish fry. Of these, 542 billion fry, or about 92 percent, were produced artificially. For marine aquaculture seed production was as follows: 3 882 million of fish fry; 58.3 billion shrimp post-larvae

According to an estimate from Fishcount, China produced much fewer (28-92 billion) farmed fish in 2015. I don’t think that the quote is a mistake because the table 7 in Li (2003) contains the same number. Furthermore, Leung et al. (2007) claim that “in 2004, 711.6 billion freshwater fish fry and 2.41 billion marine/brackish fish fry were produced in China.” Honglang (2007) claims that, according to an investigation report in 2001, there are 16 435 fish seed production units in China, and the “total production of all the hatchery is 13 385 billion individuals which meet the need for grow-out production.” The number is bigger at least partly because it includes shellfish, crabs and reptiles. Grow-out refers to a stage when individuals become bigger which suggests that these juveniles are farmed until slaughter. However, Daqing et al. (2010) cites the exact same number of fish seed production units but seems to assert that they are producing very high numbers of larvae that are stocked into natural waters:

The hybrids, transgenic and impure species should not be stocked in the natural water. [...] Currently, China has 16 435 larvae bases [...] More than 90 species are used in enhancement activities. The number of larvae of shrimp, freshwater fish and shellfish for releasing was 392.8 billion, 687.3 billion and 1262.2 billion respectively

Hishamunda and Subasinghe (2003) also claim that China has “a relatively well-established freshwater seed production technology” which suggests that seed production of a similar scale is happening in other countries as well. Kumar et al. (2018) that in India “Quantity of carp seed production has gone up to 49.5 billion fry in 2015-16.” According to an estimate from Fishcount, India produced significantly fewer (3-15.5 billion) farmed fish in 2015.

On the other hand, the number of juveniles produced by Brazil seems to be similar to the number of slaughtered fish. Suplicy (2007) claims that in Brazil “the sum of the seed production of all freshwater fish species was 617 million seed in 2005.” It seems that most of these fish are used for fish farming and less than 75 million were used for fish stocking into natural waters. The number of seeds used for aquaculture is in the range of the estimated 460-1,545 million farmed fish produced by Brazil’s aquaculture in 2015.

I am confused about what some of these big numbers are. I think they are the numbers of juveniles produced for aquaculture. But if they are, it’s unclear why these numbers of juveniles produced by India and especially by China are so much higher than estimates of slaughtered farmed fish. I’m not sure if pre-slaughter mortality rates can explain it. According to Greig (2019), “pre-slaughter mortality rates for some of the most commonly farmed fishes range from approximately 15%–80% over the entire production cycle” and “the mortality rates may be quite high in very young fishes and much lower as fishes approach slaughter.” Since hatchery-produced juveniles are already past the first stage of their lives in which pre-slaughter mortality is the highest, mortality during the grow-out period shouldn’t be that high. It could also be that the number of farmed fish that are slaughtered is higher than is estimated, but I would be surprised if it was that much higher. I think this question should be investigated further.

Endnotes

Tip: to navigate between the main text and endnotes more efficiently, you can use Ctrl + F to search for strings like “[1]”. This can help you to both, find the endnote, and get back to the part of the text where the footnote was placed.

[1] There are many synonyms for fish stocking, including stock enhancement, fisheries enhancement, fish stock propagation, ocean ranching, sea ranching, ocean ranching, marine ranching, aquaculture-based enhancement, aquaculture-based fisheries enhancement, restoration aquaculture, culture-based fisheries, and restocking. Many of these terms have slightly different meanings. For example, see definitions here.

[2] Articles that talk about fish stocking from animal welfare perspective include Brown and Day (2002), Braithwaite and Salvanes (2010), and Braithwaite and Salvanes (2011). I was unable to access Braithwaite and Salvanes (2011).

[3] I have the following disagreements with Charity Entrepreneurship’s report on fish stocking and baitfish:

• According to the report, fish stocking interventions may be less promising because the industry is on the decline. The main cited evidence for the decline is the claim in Halverson (2008) that in the U.S., "based on the data from the federal government and the 33 states for which data was available in all years, it appears that the total number of fish stocked in the 1930s was about 7 times higher than in 2004." I think that figures of the 1930s are not very relevant for determining the current trends. The graph in the trends section of this article suggests that the numbers stopped declining in the 1950s. Furthermore, Halverson (2008) also claims that the total weight of the stocked fish in the U.S. has increased dramatically since the 1930s. Finally, this evidence is only from one country and ignores much of the stocked salmon. Overall, my research in this article weakly suggests that the number of stocked fish is more likely to be increasing than decreasing. Finally, fish stocking seems likely to remain very big in scale even if it is declining.
• I think that their cited lengths of the time that fish remain in hatcheries are not representative. The evidence in this article suggests that most stocked fish spend much less than a year in hatcheries. Note that CE’s claims on this issue were based on my own preliminary research which incorrectly suggested that most fish remain in hatcheries for longer.
• The report claims that “it is also hard to increase the welfare of fish once they have been stocked.” While technically I agree with this point, I’d like to point out that Brown and Day (2002) argue that conditions in hatcheries that prepare fish for life in the wild can greatly increase the welfare after stocking.
• The report cites criticisms of fish stocking from ecological and effectiveness perspectives to claim that fish stocking is likely to be regulated in the future without any additional intervention (i.e., that it has a high “counterfactual replaceability”). While I agree that this is true, I would also like to point out that fish stocking has been practiced for over a hundred years and it doesn’t seem to be on the decline. Overall, the fact that it is criticized in other ways makes me more (not less) optimistic about the area because it makes it easier to achieve change. It means that we would have allies and that it would be more difficult for opponents to argue that fish stocking should continue.

Note that CE did not look into the issues deeply and limited the time spent on the report to 25 hours because they found it unlikely that they will decide to found a charity tackling these problems.

[4] The wording in the translation of China’s Fisheries Plan is unusual, but Mallory (2016) also assumes that the plan includes stocking 150 billion juvenile fish. The sentence in question is “计放流各类水产苗种1500亿尾”. I asked a Chinese person, and they told me that it seems only to include hatched fish, but it is vaguely defined in Chinese dictionaries.

[5] Also, Cao et al. (2017) claim that “[b]y 2008, stock enhancement was practiced for over 100 species of finfish, crustaceans, and shellfish, and almost 20 billion juveniles were released annually”.

[6] Halverson (2008) estimated that 1.75 billion fish were stocked by 50 state agencies and the U.S. Fish and Wildlife Service in the United States in 2004. The difference between the estimates is mostly due to Halverson (2008) not including most of the 1.9 billion salmon that the U.S. stocks every year.

[7] Daniels and Watanabe (2011) claims that between 1977 and 2005 Japan released 50 billion red seabream, 43 billion flounders, and 14 billion black seabream. However, I’m not sure if these numbers are correct. Figure 8 in Koichi, et al. (2015), Table 1 in this Asian Aquaculture article, and Table 1.1 in this FAO article all claim that much lower numbers of these fish were released.

[8] This is because I think that the bigger the stocking project, the more likely I was to find a number of fish stocked by it. Both, because the number was more likely to be reported, and more likely to be mentioned in the articles I read. Also, I didn’t include some smaller numbers I found from the list (they were mostly numbers of a specific fish stocked in a specific region). Finally, often I searched with a keyword “billions” because that tended to give more general and interesting results. However, it may have also biased my search towards bigger numbers.

[9] As I understand it, raising big numbers of fish requires specialized buildings, ponds (unless fish are released when they are very small), and non-trivial release operations. I think it would be difficult to do all this activity on a large scale without being detected. Furthermore, from articles like Lamp (2018), it seems that illegal stocking is done by anglers who want to improve their own angling experience. I find unlikely that they would make substantial investments into the activity. However, I am not confident that my understanding of the topic is correct.

[10] According to Stopha (2018), from 1995 to 2016 in Alaska’s salmon hatcheries, annual egg collections have ranged from about 1.6 to 2 billion eggs, and annual salmon releases have ranged from about 1.4 to 1.7 billion juveniles. This also suggests that mortality in salmon hatcheries is less than 15%. If some eggs remain unfertilized, it could be less.

[11] This article explains how to find slaughter totals within the FAO website.

[12] Fry is defined as “a recently hatched fish that has reached the stage where its yolk-sac has almost disappeared and its swim bladder is operational to the point where the fish can actively feed for itself.” Before yolk-sac disappears, salmon and trout are called alevin. How long the alevin stage lasts depends on water temperature (Ojanguren et al. (1999)) and species:

• Park et al. (2017) claim that the common carp (and most other cyprinids) absorb their yolk sac in 4-5 days.
• This hatchery brochure claims that its trout are alevins for 4-6 weeks. FAO claims that steelhead trout’s yolk sac lasts for 2-4 weeks.
• In nature, salmon remain alevin for a few weeks or a few months. In hatcheries, conditions are optimized for fast growth, so yolk sac is probably absorbed in less than a month.

FAO (2003) refers to 7-day-old stocked fish as fry. Pennsylvania Fish & Boat Commission claims that fry are “[t]ypically between 3 and 5 days old. These fish are distributed to public fishing waters at a time soon after hatching while the yolk sac is being absorbed.” It calls 21-day-old fish advanced fry. Neither of these sources mentions species. An FAO page claims that alevins can also be referred to as yolk-sac fry which suggests that the word fry can be used for juveniles regardless of whether their yolk-sac is absorbed. Overall, I’m uncertain how old are stocked fish which are referred to as fry.

[13] Fingerling is defined as “a young fish, especially one less than a year old and about the size of a human finger.” According to the Pennsylvania Fish & Boat Commission, “depending upon the species, these fish are 3 or more months in age.” However, Horváth et al. (1985) claim that “the intensive production of advanced carp fry about 3 cm long, in well prepared earthen ponds, takes 21-30 days. They are then transported to fingerling ponds for further rearing” which suggests that carp can be called fingerling when they are 21 days old or older.

[14] In addition, Monacelli (2015) claims that some fish stocked in New Jersey in 2015 would be “young,” and others would be between 2.5 and 3.5 years old. These older large fish were used to obtain and fertilize eggs for the breeding program in a hatchery. Spence (2013) mentions seeing 13 kilogram trout in hatcheries. I guess that such big fish were also used to obtain fertilized eggs.

[15] Another example of variance can be seen in Alaska’s database of sport fish stockings. Stocked fish vary from less than 0.1 oz. (3 grams) to 3 lbs., 7.1 oz. (1.6 kg). There is even a lot of variance in the size of individuals of the same species stocked in the same lake.

[16] See figure 6 in NPAFC Statistics: Pacific Salmonid Catch and Hatchery Release Data.

[17] Many of these hatcheries are open to visitors, perhaps some more information can be gained this way if needed. The main value would probably come from asking questions.

[18] I’m not sure if these survival rates are typical, or if Brown and Day (2002) cited the lowest survival rates to illustrate the point. Kennedy et al. (2012) claim similarly low survival rates of hatchery-bred salmon. Lymbery (2002) cites much higher survival rates for salmon (between 6% and 40%) and say that they are comparable with 10% of wild salmon returning to their home river after maturing at sea. Overall, survival after the release undoubtedly depends on many factors that are beyond the scope of this article.

[19] Braithwaite and Salvanes (2010) claims that

Many of the fish proteins and oils are now being replaced with plant-based products, but from a welfare perspective, the use of plant protein and oils in a carnivorous fish diet is not natural. The effects of new feeds must be carefully assessed, not just in terms of growth rate of the farmed fish, but also in terms of the effect they have on appetite and hunger. Current research is focusing on ways to manufacture more vegetable-based feeds or feeds based on other sources of protein, such as poultry.

Also, note that very young fish seem to be often fed live invertebrates (such as brine shrimp and rotifers).

[20] It’s possible that prohibiting fish stocking for the benefit of recreational fishers could increase the scale of illegal stocking. The number of fish stocked illegally would probably still be much lower than the number of fish stocked today. However, if illegal stocking would be done with less awareness of the impact on the ecosystem, it could still cause significant environmental damage.

[21] Some animal rights activists are against many of the changes that the animal welfare movement is campaigning for. They argue that these changes can be counterproductive in the long term because they send the message that treating animals as property can be acceptable. This sometimes leads to infighting which can reduce the legitimacy of animal advocacy as the whole. For example, PETA opposed California's Prop 12 which demanded better conditions for farmed animals. Furthermore, the opposition to Prop 12 was entirely funded by a nominally farm-animal protection organization (HFA) which claimed that Prop 12 is bad for animals. HSUS accused HFA of misinformation. Preventing such infighting is one of the reasons why it’s preferable to focus on interventions that are good from both, Animal Rights and Animal Welfare perspectives.

[22] Cooke and Cowx (2004) extrapolated from Canada’s statistics from the year 2000 that the total annual recreational catch worldwide may be on the order of 47 billion fish. It should be noted that the number of fish caught in Canada decreased from 233 million in 2000, to 194 million in 2015, of which 135 million were released. Furthermore, it’s unclear whether Canada is representative of the World as a whole in this regard. Funge-Smith et al. (2018) estimated that of the countries where some data are available (combined population 2.6 billion), some 6.7% (174.5 million) of the population engages in recreational fishing in inland waters at some time in a year. The percentage for Canada is only slightly bigger than average (7.5%). However, I expect the percentage of recreational fishers in countries for which data is not available to be lower.

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This essay is a project of Rethink Priorities. It was written by Saulius Šimčikas. Thanks to David Moss, Derek Foster, Karolina Sarek, Marcus A. Davis, and Peter Hurford for reviewing drafts of this post and making valuable comments. I want to especially thank Kieran Greig who made very many valuable suggestions.