The American cockroach (Periplaneta americana) residue could partially replace the dietary fish meal in the juvenile Nile tilapia (Oreochromis niloticus)

The American cockroach (Periplaneta americana) residue is a by-product of P. americana meal after extracting active ingredients with ethanol, and it still contains high protein, lipid, and a certain amount of active ingredients, may be a potential fish meal alternative. Five isonitrogenous and isolipidic experimental diets were formulated to replace 0%, 25%, 50%, 75%, and 100% of dietary fish meal with P. americana residue, and defined as Diet 1, Diet 2, Diet 3, Diet 4, and Diet 5, respectively. The juvenile Nile tilapia (Oreochromis niloticus) with an initial body weight of 2.98 ± 0.01 g was fed with respective diets for 10 weeks, which was conducted to investigate the effects of dietary fish meal replacement by P. americana residue on the growth performance, proximate composition, amino acid profile, metabolism, antioxidant capacity, and immunity of juvenile O. niloticus. There were no significant differences in the final body weight, weight gain rate, and specific growth rate among five diet groups, while the highest feed conversion ratio and the lowest protein efficiency ratio were recorded in Diet 4. There were no significant differences in the contents of crude protein, total lipid, ash, and total amino acid in the whole fish body among all groups. The Diet 1 and Diet 2 had higher activities of trypsin, α-amylase, and chitinase in the intestine and α-amylase in the liver. The highest serum urea content was detected in Diet 4, while the lowest liver urea content and the highest serum total protein content were detected in Diet 3. A higher liver catalase, glutathione peroxidase, and serum lysozyme activities were detected in Diet 2, and the lowest serum malondialdehyde content was detected in Diet 2. In conclusion, dietary fish meal replacement by the P. americana residue had no negative effects on the growth performance and body composition of juvenile O. niloticus, and significantly improved the antioxidant capacity and immunity, while feed utilization rate was reduced when dietary fish meal replacement levels exceeded 75%.