Fish stocking 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 6 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.
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.