In winter, rotenone may remain toxic for more than 30 days. Tempering Before stocking fish in a pond, adjust the water in the transport tank holding the fingerlings to match the pond water in temperature and other water quality factors such as pH, alkalinity, and hardness. As a general rule, catfish can withstand a 5 degree F change in temperature without severe stress and a 10 degree F change if the water is tempered over a period of 30 minutes. For greater temperature differences, care must be taken to slowly equalize water temperatures before moving the fingerlings from the tank to the pond. In this case, adjusting water temperature 1 degree F every 10 minutes is a good rule to follow.
Tempering is especially important if fish are going from cool water to warm water.
Insufficient tempering can kill the fish by temperature shock or shock from other water quality factors. If the fish are not killed by the shock, they can be weakened, which lowers their resistance to disease. Starting with good quality, healthy fingerlings of known genetic background is very important to profitably growing a crop of fish. Buy your fingerlings from a producer who has a reputation for producing good fish, who knows how to treat fish for disease, who has the equipment and the know-how to handle them without excessive stress, and who delivers accurate counts and weights.