Effects of White Fish Meal Replaced by Low-Quality Brown Fish Meal with Compound Additives on Growth Performance and Intestinal Health of Juvenile American Eel (Anguilla rostrata)

SIMPLE SUMMARY: There is a high demand for white fish meal in the diet of eels (Anguilla spp.). A reduced supply and higher price of white fish meal heavily limit the sustainability of the eel aquaculture industry. It is essential to explore a practical strategy to reduce the consumption of white fish meal. In the current study, we investigated the effects of low-quality brown fish meal with compound additives to replace the high-quality white fish meal on the parameters of growth and intestinal health status of juvenile American eels (Anguilla rostrata). The results implied that low-quality brown fish meal combined with compound additives could successfully replace 20% white fish meal without adversely affecting the intestinal health status of this fish species. ABSTRACT: With a reduced supply and increased price of white fish meal (WFM), the exploration of a practical strategy to replace WFM is urgent for sustainable eel culture. A 70-day feeding trial was conducted to evaluate the effects of replacing WFM with low-quality brown fish meal (LQBFM) with compound additives (CAs) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata). The 300 fish (11.02 ± 0.02 g/fish) were randomly distributed in triplicate to four groups (control group, LQBFM20+CAs group, LQBFM30+CAs group and LQBFM40+CAs group). They were fed the diets with LQBFM replacing WFM at 0, 20%, 30% and 40%, respectively. The CAs were a mixture of Macleaya cordata extract, grape seed proanthocyanidins and compound acidifiers; its level in the diets of the trial groups was 0.50%. No significant differences were found in the growth performance between the control and LQBFM20+CAs groups (p > 0.05), whereas those values were significantly decreased in LQBFM30+CAs and LQBFM40+CAs groups (p < 0.05). Compared to the control group, the activity of glutamic-pyruvic transaminase was significantly increased in LQBFM30+CAs and LQBFM40+CAs groups, while lysozyme activity and complement 3 level were significantly decreased in those two groups (p < 0.05). There were decreased antioxidant potential and intestinal morphological indexes in the LQBFM30+CAs and LQBFM40+CAs groups, and no significant differences in those parameters were observed between the control group and LQBFM20+CAs group (p > 0.05). The intestinal microbiota at the phylum level or genus level was beneficially regulated in the LQBFM20+CAs group; similar results were not shown in the LQBFM40+CAs group. In conclusion, with 0.50% CA supplementation in the diet, LQBFM could replace 20% of WFM without detrimental effects on the growth and intestinal health of juvenile American eels and replacing 30% and 40%WFM with LQBFM might exert negative effects on this fish species.