Optimization of Selenium Inclusion Level in the Larval Diet of Labeo rohita

The nutritional requirement of fish larvae remains a limiting factor in advanced aquaculture. Micronutrients are crucial for early development, but their dietary inclusion level in the larval feed of carps has not been standardized. The present study was executed to determine the optimum dietary inclusion level of organic and inorganic selenium in the larval feed of Rohu, Labeo rohita. A 35-day feeding trial in triplicate under semi-control conditions was conducted in 21 troughs divided into seven groups. Each trough (capacity 4.0 L) contained 200 larvae (average body weight 0.4 mg). The first group (control) was reared on nano-particulate basal diet (CP 50%), while three groups Se-Na_(0.5), Se-Na₍₁₎, and Se-Na_(1.5) were fed basal diet supplemented with graded levels (0.5-1.5 mg/kg diet) of inorganic form of Se, sodium selenite (Se-Na). The last three groups (Se-Met_(0.5), Se-Met₍₁₎, and Se-Met_(1.5)) were fed organic form of dietary Se, selenium methionine (Se-Met) at the same inclusion level as Se-Na. Results indicated the curvilinear relationship of dietary Se levels with body weight, activity of digestive enzymes (protease, amylase, lipases, and trypsin), and antioxidant enzymes (SOD, CAT, POD, and GSH-Px) activity, intestinal villi, width, and absorptive area. A positive correlation was observed with up to 0.5 and 1 mg/kg diet of Se-Na and Se-Met, respectively; however, above these levels, a negative impact was observed. The upregulation of growth hormone mediator (IGF-1) and downregulation of heat shock protein (HSP-70) also followed a similar trend in response to Se-Na and Se-Met inclusion. Based on the results, 1 mg/kg diet Se-Met could be considered the optimum level and is recommended for the early rearing of rohu larvae.