Tilapia farming: Dwarfism is a response to overcrowding stress

Tilapia living in crowded aquaculture ponds or small freshwater reservoirs adapt so well to these stressful environments that they stop growing and reproduce at a smaller size than their stress-free counterparts.

source https://phys.org/news/2021-03-tilapia-farming-dwarfism-response-overcrowding.html