The use of microalgae as a supplement on growth, reproductive performance, antioxidant defenses and nutrigenomics profiling in zebrafish (Danio rerio) and pacu (Piaractus mesopotamicus)

Abstract

The rapid global expansion of the aquaculture and the restricted production of fish meal (FM) has considerably increased the demand for alternative sources of protein in fish diets. Plant-based proteins have been favored as substitutes for FM. However, the presence of antinutritional factors may limit their use. On the other hand, microalgae have been increasingly incorporated as a supplement in fish feed. Microalgae, especially chlorella (Chlorella sp) and spirulina (Arthrospira platensis), have attracted attention due to their high protein content, adequate amino acid profile, fatty acids, antioxidant and immunostimulating compounds. This study provides results in three different approaches. In the first one: zebrafish (Danio rerio) was subjected to a feeding test, in which up to 100% of the FM was replaced by Chlorella sp (CM) in 0, 10, 20, 30, 40, and 50 g/kg diet. After 60 days of feeding, the animals fed 40 g/kg CM showed significantly greater growth compared to the group that received a diet without CM. The lowest levels of total cholesterol, LDL and triglycerides were observed in fish fed 50 g/kg CM. The CM levels significantly increased alkaline phosphatase activity in fish. Diets containing 40 and 50 g/kg CM provided the highest egg production, hatching rate, and larvae survival at 6 days after fertilization. The second study aimed to evaluate the effects of replacing FM by spirulina (SM - A. platensis) in zebrafish diets on growth, reproductive performance, and gene expression through RNA sequencing (RNA-Seq). The feeding test consisted of replacing FM is up to 100% with spirulina in 0, 10, 20, 30, 40 and 50 g/kg diet. Animals fed 50 g/kg SM showed significantly higher growth and reproductive performance than animals fed a diet without spirulina. RNA-Seq revealed that fish fed 50 g/kg spirulina positively regulated the expression of genes related to growth and immunity. The third study evaluated the dietary substitution effect of FM with spirulina in pacu juveniles (Piaractus mesopotamicus) on growth and serum biochemical parameters. Antioxidant responses were also evaluated before and after the ionized ammonia challenge. The fish were fed six experimental diets formulated to contain different spirulina levels (0, 20, 40 and 60 g/kg) to replace FM. Fish fed diets 40 and 60 g/kg spirulina showed better growth and lower levels of total cholesterol, triglycerides, LDL, and alanine aminotransferase. Diets containing 40 and 60 g/kg spirulina increased activities of catalase, superoxide dismutase and total antioxidant capacity. Liver concentrations of malondialdehyde differed only after exposure to ammonia. The results suggest that both chlorella and spirulina can be used in zebrafish and pacu diets.