Nutritional comparison and evaluation of two macroalgae, Sargassum ilicifulium and Padina australis, as partial substitution with fish meal in practical diets of Asian sea bass juvenile (Lates calcarifer)

Abstract

Abstract In this study, we used Asian seabass (Lates calcarifer) with initial weight of 29.0 ± 1.0 g as the model organism to investigate the effects of dietary Sargassum ilicifolium and Padina australis on various aspects of growth and immune response. We formulated three diets in which fish meal (FM) was gradually replaced by S. ilicifolium (SIM) and P. australis meal (PAM) at a substitution level of 6% (SIM 6 (S6) and PAM 6 (P6)). The control diet (C) did not contain any macro algae. Our findings revealed that the group given the P6 diet exhibited significantly higher growth and feed utilization than the control group (P < 0.05). Our findings indicate that the inclusion of P. australis in the diet had a significant impact on red blood cells (RBC), haemoglobin (Hb), hematocrit (Hct), white blood cells (WBC), lymphocytes, neutrophils, and cholesterol (P < 0.05). Furthermore, the S. ilicifolium diet resulted in significantly higher levels of total protein and triglyceride in the fish as compared to the other groups (P < 0.05). Our study showed that the group fed with 6% P. australis had significantly higher levels of immunoglobulin and lysozyme in both skin mucus and serum compared to the control group (P < 0.05). Furthermore, the group fed with 6% S. ilicifolium exhibited significantly higher levels of serum immunoglobulin (P < 0.05). However, there were no significant differences in alternative complement activity and serum lysozyme among all treatment groups (P > 0.05). After evaluating the activity of digestive enzymes, including protease, lipase, and amylase, we observed no significant differences among the treatment groups (P > 0.05). Additionally, we measured the expression levels of growth-related genes, such as insulin-like growth factor I (IGF-I), lysozyme (LZ), and interleukin-1β (IL-1β). Our findings indicate that the P6 group had significantly higher expression levels of these genes compared to all other treatment groups (P < 0.05). In conclusion, our research demonstrates that incorporating Padina australis into the diet of Asian seabass juveniles and partially replacing fish meal has positive effects on their immune system and growth performance.