Nutritional effects of protein source in starter diets for channel catfish(Ictalurus punctatus Rafinesque) in suboptimal water temperature

Intensive tank rearing of channel catfish (Ictalurus punctatus Rafinesque) fry can be successfully accomplished with commonly available 'salmonid' sta rter diets. Ingredient substitution in starter diets is less important from the cost perspective but growth, survival and health of fish are major con cerns. Several combinations of fish meals and animal protein substitutes we re evaluated in diet formulations for hatchery rearing of catfish fry. Sub- optimal thermal conditions were used which are characteristic for the north -central USA where catfish culture is important for stocking purposes and l ive-fish markets. A diet formulated on the basis of menhaden fish meal (29. 1%), herring fish meal (25.1%) and animal by-product mixture (16.38%) gave numerically the highest growth rate after 13 weeks of feeding, although gro wth reductions in fish fed diets exclusively with mehaden meal (77.6%) as p rotein or substituted with 50% animal by-product protein were not significa nt. Instantaneous mortality rates were the highest between weeks 2 and 4 of rearing and increased almost proportionally with the increased fish meal p rotein substitution. A diet based on menhaden fish meal had the highest con centration of phosphorus and several other essential minerals, but these we re not reflected in the mineral composition of the fish body at the termina tion of feeding. Among activities of digestive enzymes, trypsin was depress ed in fish offered diets with 75-100% fish meal protein replacement. A diet superior in terms of fish performance was defined in the present study and it was concluded that the initial feeding can greatly affect physiological status of juvenile channel catfish.