A feeding trial was conducted to assess the effects of dietary American cockroach Periplaneta americana meal (PAM) inclusion on the growth performance, antioxidant capacity, and immunity of juvenile rainbow trout Oncorhynchus mykiss. Five isonitrogenous and isolipidic diets were formulated to contain 100, 150, 200, 250, and 300g/kg PAM (defined as PAM100-PAM300), respectively. The final body weight and weight gain rate of PAM250 were significantly higher than those of PAM100 and PAM150, and a higher specific growth rate was recorded in PAM200-PAM300. The highest levels of liver alanine aminotransferase and serum aspartate aminotransferase (AST) as well as serum total amino acids were detected in PAM150, while higher levels of liver AST and serum total protein were detected in PAM200-PAM300. The liver lipase activity of PAM150, PAM200, and PAM300 was significantly higher than that of PAM100. The liver glucose content in PAM150 was significantly higher than that in PAM250-PAM300. The highest liver catalase, alkaline phosphatase (AKP), and lysozyme activities were detected in PAM300; the lowest liver malondialdehyde content was detected in PAM250, while the highest serum total antioxidant capacity, catalase, and total superoxide dismutase activities were detected in PAM250. The highest serum AKP and acid phosphatase activities were detected in PAM150, while higher serum IgM and complement C3 contents were detected in PAM200-PAM300. In conclusion, dietary PAM inclusion at 200-300g/kg could improve the growth performance, antioxidant capacity, and immunity of juvenile O. mykiss.

Astaxanthin is an important pigment for the rainbow trout Oncorhynchus mykiss. This study was conducted to investigate the effects of different sources of dietary astaxanthin on the growth, coloration, and antioxidant capacity of the commercial-sized O. mykiss during long-term feeding. Haematococcus pluvialis (HP), yeast Phaffia rhodozyma (PR), and synthetic astaxanthin (SA) were added to the basic feed (no astaxanthin, NA) to prepare the isonitrogenous and isolipidic experimental diets; the actual astaxanthin content values in the diets were 31.25, 32.96, and 31.50 mg/kg, respectively. Eighteen hundred O. mykiss, averaging 670 ± 20 g, were randomly divided into four groups and then fed with the experimental diet for four months. Dietary supplementation of P. rhodozyma and synthetic astaxanthin had no significant effects on the growth and tissue indexes of O. mykiss. In contrast, dietary supplementation with astaxanthin from H. pluvialis significantly increased the weight gain rate after four months of feeding. The fillet lightness of O. mykiss in the PR and SA was statistically lower than that in the NA and HP; the redness and astaxanthin content of fillet in the HP, PR, and SA groups were statistically higher than those in the NA. The total antioxidant capacity of the liver and serum in the HP was statistically higher than that in other diet groups, and a higher liver total superoxide dismutase activity was detected in the HP compared with the PR. Dietary supplementation of astaxanthin significantly increased the glutathione peroxidase activity in the liver and serum, and the highest serum glutathione peroxidase activity was detected in the HP, while dietary astaxanthin significantly decreased the malondialdehyde content in the liver and serum. Dietary supplementation of PR significantly increased the fillet ash content, while the highest fillet total lipid content was detected in the HP. Dietary astaxanthin significantly improved fillet redness and antioxidant capacity, among which H. pluvialis astaxanthin has greater effects on improving weight gain, antioxidant capacity, and fillet total lipid content.

Astaxanthin is an important aquatic feed additive that enhances the antioxidant capacity, and immune function of rainbow trout (Oncorhynchus mykiss); however, very limited information is available on its underlying molecular mechanisms. Haematococcus pluvialis powder, Phaffia rhodozyma powder, and synthetic astaxanthin were added to the commercial feed (no astaxanthin, NA) to prepare three experimental feeds, referred to as the HPA, PRA, and SA groups, respectively, and their actual astaxanthin contents were 31.25, 32.96, and 31.50 mg.kg^-1, respectively. A 16-week feeding trial was conducted on the O. mykiss with an initial body weight of 669.88 ± 36.22 g. Serum and head kidney samples from commercial-sized O. mykiss were collected for metabolomics and transcriptomics analysis, respectively. Metabolomics analysis of the serum revealed a total of 85 differential metabolites between the astaxanthin-supplemented group and the control group. These metabolites were involved in more than 30 metabolic pathways, such as glycerophospholipid metabolism, fatty acid biosynthesis, linoleic acid metabolism, and arginine and proline metabolism. It is speculated that different sources of dietary astaxanthin may regulate antioxidant capacity and immunity mainly by affecting lipid metabolism and amino acid metabolism. Transcriptomic analysis of the head kidney revealed that the differentially expressed genes between the astaxanthin-supplemented group and the control group, such as integrin beta-1 (ITGB1), alpha-2-macroglobulin (A2M), diamine acetyltransferase 1 (SAT1), CCAAT/enhancer-binding protein beta (CEBPB) and DNA damage-inducible protein 45 alpha (GADD45A), which are involved in cell adhesion molecules, the FoxO signaling pathway, phagosomes, and arginine and proline metabolism and play regulatory roles in different stages of the antioxidant and immune response of O. mykiss.

Five isonitrogenous and isolipidic diets (Diet 1–Diet 5, with Diet 1 as the control) were formulated to replace 0%, 20%, 40%, 60%, and 80% of fishmeal with American cockroach residue. Juvenile Cyprinus carpio (initial body weight approximately 74 g) were randomly assigned to these diets for a 10-week feeding trial. The Diet 3 group (40% replacement) showed significantly higher final body weight, weight gain rate, specific growth rate, and protein efficiency ratio compared to other groups. No significant differences were observed in crude protein, ash, and total amino acid content across the diets. Groups fed Diet 1 and Diet 2 exhibited higher intestinal trypsin, lipase, α-amylase, and hepatic trypsin activities. Serum triglyceride (TG) levels were highest in the Diet 5 group. Hepatic aspartate aminotransferase (AST) activity was significantly lower in the Diet 3 and Diet 5 groups compared to Diet 1. Serum urea nitrogen levels followed a non-linear trend, initially increasing, then decreasing, and rising again with increasing fishmeal replacement. No significant differences were found in serum total protein (TP) levels among the dietary groups. Intestinal villus number, muscle layer thickness, villus height, villus width, and crypt depth remained consistent across groups. However, goblet cell numbers were significantly reduced at the 60% replacement level, which could impair intestinal barrier function. Diet 3 showed higher serum and hepatic total superoxide dismutase (T-SOD) activity, while Diet 2 had the highest hepatic total antioxidant capacity (T-AOC) activity. Hepatic malondialdehyde (MDA) levels were lowest in the Diet 2 and Diet 5 groups. Immunoglobulin M (IgM) levels showed an increasing trend with higher fishmeal replacement levels. In conclusion, replacing fishmeal with American cockroach residue did not adversely affect growth performance or body composition in juvenile C. carpio. Substituting 20–40% of fishmeal with American cockroach residue enhanced antioxidant capacity and immune function in juvenile C. carpio.