Once the decision has been made as to what to stock, it is important to follow the proper procedures to maximize the health and survival of the fingerlings purchased. If survival of one or another type of fish being stocked is low, actual numbers will differ greatly from the recommended rates, and pond balance may be difficult to establish or maintain. In some instances, high mortality shortly after stocking may go unnoticed. For this reason, every effort must be made to minimize stress during transport and stocking. Acclimation Procedures
Fingerlings for stocking are generally transported in hauling tanks with aeration or in sealed bags with oxygen. Upon arrival, gradually replace water in hauling tanks with water from the pond to be stocked. This can be done with a small pump or with buckets. Adjust temperature gradually, with no more than a 7-8 degree F increase or a 5 degree F decrease per half hour. Continue aeration during this process. When temperatures have been adjusted, transfer fish to the pond as gently as possible, with minimal handling.
If fingerlings arrive in sealed plastic bags, float the bags in a shady area for 30 minutes, then open them and immediately release the fish. Normally, pond water should not be gradually mixed with shipping water in bags. Carbon dioxide and ammonia build up in shipping bags during transport. Since these compounds cannot dissipate into the atmosphere, dissolved carbon dioxide reaches very high levels, lowering the pH of the shipping water. Opening the bags allows the carbon dioxide to escape rapidly, and aerating or splashing accelerates this process. The pH rises drastically, and any ammonia present rapidly converts to the toxic form. This chain of events will kill fry and small fingerlings quickly.
This problem is less serious when transport times are short and when fish have not been fed for several days. Gradual mixing of pond water with transport water in bags (after temperature adjustment) is usually desirable only when moving young fish from hard water to moderately or very soft water. When attempting this procedure, monitor the fish closely for signs of stress, and introduce them directly into the pond if they begin to appear weak or disoriented.