Effects of dietary inclusion of the beta-adrenergic agonist, salbutamol, on growth performance and whole-body composition of rohu Labeo rohita (Hamilton) fingerlings fed diets containing two protein levels

A 60-day feeding experiment was conducted in the laboratory to evaluate the effect of oral administration of the beta-adrenergic agonist (BAA), salbutamol, on growth, nutrient utilization and whole-body composition of rohu Labeo rohita (Hamilton) fingerlings (average weight 5.51 ± 0.07 g) acting as a repartitioning agent in intermediary metabolism and redistributing nutrients for muscle synthesis. Two diets (diets 30/0 and 40/0) were formulated containing 30% and 40% crude protein to serve as basal diets containing the same ingredient composition. Another four diets (diets 30/3, 30/6, 40/3 and 40/6) were prepared in the same way to contain either 3 or 6 mg kg^?1 BAA salbutamol at each protein level making the total of six experimental diets. Rohu fingerlings were fed with the experimental diets in three replicate treatments at a restricted feeding regime equivalent to 2% of body weight (BW) day^?1. A significant (P < 0.05) interaction effect was found between dietary protein level and BAA treatment. Dietary incorporation of BAA at both protein levels significantly (P < 0.05) increased growth and nutrient utilization in terms of weight gain (%), specific growth rate (SGR), feed:gain ratio (FGR) and protein efficiency ratio (PER). BAA treatment at the 6 mg kg^?1 concentration led to a 12% rise in growth with the 30% protein diet and a 6% rise with the 40% protein diet, above their respective controls (without BAA treatment). However, no significant differences were found by raising the BAA concentration from 3 to 6 mg kg^?1. The apparent digestibility values for protein, lipid and energy were only higher with the 30% protein diets containing BAA. At both protein levels tested, BAA exerted a significant (P < 0.05) positive influence on protein retention and a negative influence on lipid retention efficiency, although the differences between the 3 and 6 mg kg^?1 BAA diets were not significant. This indicated that BAA acted as a repartitioning agent in suppressing lipid deposition in favour of protein accretion. BAA induced significantly (P < 0.05) higher whole-body protein and lipid relative to the untreated groups. The condition factor improved significantly (P < 0.05) in the BAA-treated dietary groups. The fillet percentage displayed a direct correlation and the frame percentage a negative correlation with BAA concentration in the diets. The results indicate that the BAA, salbutamol, was effective in producing growth enhancement, improved body composition (higher protein and lower lipid accretion) and efficient nutrient utilization at the 3 mg kg^?1 dietary incorporation level and thus has a potential for application in formulated diets for the Indian major carp, rohu, under culture conditions.