Fucoidan-rich Sargassum wightii extract supplemented with α-amylase improve growth and immune responses of Labeo rohita (Hamilton, 1822) fingerlings

Fucoidan-rich seaweed extract (FRSE) was prepared from Sargassum wightii by modified alcohol-water extraction method. A 45-day feeding trial was conducted to evaluate the individual and combined effect of fucoidan-rich seaweed extract (FRSE-20 g kg(-1)) and exogenous alpha-amylase (100 mg kg(-1)) on the growth response, metabolic enzymes, immune parameters, and amylase gene expression of Labeo rohita. Four purified iso-nitrogenous diets (350 g CP kg(-1) feed) with different combinations of alpha-amylase were prepared. Among the various treatment groups, the group fed with FRSE along with amylase group exhibited significantly higher (p < 0.05) weight gain, SGR, PER, liver metabolic enzyme activities, and lower FCR than the control group. The hematological and serum parameters such as NBT, erythrocyte count, plasma protein, albumin and globulin values were significantly higher (p < 0.05) in the FRSE fed groups. LDH activities and antioxidant enzyme activities reduced significantly in FRSE fed groups, whereas activities were significantly higher (p < 0.05) in the alpha-amylase fed and control groups. The intestinal amylase activities were significantly higher in the alpha-amylase fed groups, while expression of amylase gene mRNA was significantly lower in the alpha-amylase-supplemented groups (p < 0.05). There was no significant difference between control and FRSE fed groups in both, intestinal amylase activities and amylase gene mRNA expression. Overall results confirmed that FRSE extracted from S. wightii enhances immune responses, but not the growth. Further, it does not show any evidence of an inhibitory effect on intestinal amylase activity as well as on the mRNA levels. Hence, the alpha-amylase supplementation at 100 mg kg(-1) with 20 g kg(-1) FRSE in L. rohita fingerlings diet provides growth-promoting effect without compromising its immune-modulating effect.