Effects of dietary supplementation with Sargassum horneri meal on growth performance, body composition, and immune response of juvenile turbot

Seaweed in the diet has been widely reported to improve growth and immunity of fish. In China, a large bloom of Sargassum horneri occurred in 2017, which provided biomass for potential development and utilization in the aquaculture industry. The goal of this study was to evaluate the effects of S. horneri meal as a dietary supplement on the growth performance, body composition, and immune response of juvenile turbot (Scophthalmus maximus). A basal diet was supplemented with increasing amounts of S. horneri meal to formulate five groups of experimental diets containing 0, 2.5%, 5%, 7.5%, and 10% S. horneri meal (denoted as SH0, SH2.5, SH5, SH7.5, and SH10). Turbot juveniles (initial weight 66.45 +/- 0.52g) were fed experimental diets for 8weeks. Final results showed similar growth performance and biometric indices among the diets. Fish fed with S. horneri meal had weight growth rates ranging from 85.03 to 88.12%, which were comparable to those of the SH0 group (90.50%). Crude protein content of whole fish increased linearly with increasing dietary S. horneri content, whereas crude fat content increased first and then decreased. The concentrations of serum cholesterol, high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) increased linearly with increasing amounts of dietary S. horneri, but the LDL-C/HDL-C ratio did not change significantly (P>0.05). Activities of serum non-specific immune enzymes (acid phosphatase and catalase) gradually increased with increasing levels of dietary S. horneri. Challenge with the bacterium, Edwardsiella tarda revealed that fish fed the SH0 diet had lower disease resistance compared to those fed the diets containing S. horneri. Under the present experimental conditions, S. horneri meal could be used as an ingredient contributing up to 10% of the diet for juvenile turbot with no negative effects on growth performance. Inclusion of S. horneri in the diet enhanced the activity of non-specific immune enzymes and resistance to pathogenic bacteria. However, higher levels of S. horneri meal also inhibited intestinal lipase activity and reduced lipid deposition in the fish body.