Take responsibility for your aquarium fish and either trade them to other aquarium owners or dispose of them properly. Better yet, know what size a species will likely attain before you purchase the fish and do not buy fish that will get too big for your aquarium. Fish die-offs are common in the spring. Lake residents and pond owners who find small numbers of dead fish along their shorelines in the spring need not worry in most cases. Minor fish die-offs commonly occur each year during early spring and late summer.
Fish are more susceptible to stress during spring.
Poor conditions in summer and fall can magnify the effects of food scarcity in winter. As the weather warms in spring, bacteria and other pathogens may infect fish. On top of this, fish are physically gearing up for the coming spawning season. All these factors produce stress that some individual fish simply cannot overcome. Stressful environmental conditions usually take their toll on weak or unhealthy fish.