I've read somewhere that fish excrete a type of pheromone (thru their gills) that has a population control effect. It is also probably related to reduced size.
I remember an interesting pond that I saw in Japan which had MASSIVE koi in it... the pond was constantly flushed by a fresh water stream (no filter) and the koi were about 40" long and who knows how heavy. I've seen a lot of other koi ponds in Japan, Hawaii and elsewhere, but despite the cold weather, those koi were the biggest I've ever seen (bigger even than the koi in the Nagasaki river, where were pretty huge).
I remember an interesting pond that I saw in Japan which had MASSIVE koi in it... the pond was constantly flushed by a fresh water stream (no filter) and the koi were about 40" long and who knows how heavy. I've seen a lot of other koi ponds in Japan, Hawaii and elsewhere, but despite the cold weather, those koi were the biggest I've ever seen (bigger even than the koi in the Nagasaki river, where were pretty huge).
