Incorporating hydrolyzed soy protein or black soldier fly (Hermetia illucens) larvae meal into feeds for Totoaba macdonaldi

A 7-week study was conducted to evaluate the replacement of fishmeal (FM) by hydrolyzed soy protein (HSP) or black soldier fly larvae meal (BSFM) in diets for Totoaba macdonaldi juveniles (2.5 +/- 0.1 g). A control diet containing FM as the main protein source was formulated with crude protein and crude fat contents of 52% and 14%, respectively. Then, in a series of isoproteic and isocaloric diets, HSP was incorporated at levels of 15 and 25%, or partially defatted BSFM at levels of 25 and 40%, in place of FM by weight. Fish fed the control diet and the diet containing HSP at 15% FM replacement had similar performance across all growth parameters, feed utilization, and body indices. In contrast, fish fed HSP at 25% FM replacement had significantly inferior final weight (46.59 g) and FCR (1.19). Fish fed BSFM at both levels of inclusion (25 and 40%) resulted in significantly reduced growth (final weight of 48.11 and 42.8 g, respectively) and also worse FCR (1.06 and 1.30, respectively), as compared to fish fed the control diet (final weight and FCR of 59.72 g and 0.94, respectively). Minimal changes in whole body proximate composition of fish and no changes in proximate and amino acid composition of muscle tissue were observed in response to dietary HSP or BSFM. Compared to fish fed the control diet, the fold change in trypsin gene expression increased significantly in fish fed 25% HSP, but not in fish fed 15% HSP. A similar numerical trend was observed for chymotrypsin gene expression, although differences were not statistically significant (P = 0.0768). No significant differences were observed for the gene expression of both enzymes in response to dietary BSFM; regulation of both proteases appears to take place at a transcriptional level. In summary, at least 15% of dietary fishmeal can be replaced by HSP without altering growth, survival, or any feed utilization and body indices of T. macdonaldi juveniles. Conversely, fish fed diets replacing 25% FM by HSP or by 20 and 40% BSFM displayed significantly inferior growth.