Dietary Arginine Requirement for Blunt Snout Bream (Megalobrama amblycephala) with Two Fish Sizes Associated with Growth Performance and Plasma Parameters

This trial was conducted to investigate the dietary arginine requirement in two sizes of blunt snout bream (Megalobrama amblycephala). Six isonitrogenous and isoenergetic (34% crude protein) diets containing graded levels of arginine from 8.3 to 33.6 g kg(-1). Triplicates of 30 fishes (body weight 52.50 +/- 0.18g) of size I or 20 fishes (body weight 101.85 +/- 1.85g) of size II were fed with one of six experimental diets. Specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER) and weight gain (WG) significantly increased with the increase of arginine levels from 8.3 to 23.5 g kg(-1) (size I) or from 8.3 to 18.1 g kg(-1) (size II), and thereafter, kept decrease. The alanine aminotransferase (ALT) was significantly decreased with increase in dietary arginine levels from 8.3 to 23.5 g kg(-1) in size I or 8.3 to 18.1 g kg(-1) of the size II (P<0.05). Urea content first significantly increased (P<0.05), and showed the same trend in two sizes. Meanwhile, plasma arginine concentration of two sizes significantly increased with increasing dietary arginine from 8.3 to 23.5 g kg(-1) (P<0.05), and significantly lower lysine content in plasma was observed in fish fed diets with arginine levels from 8.3 to 23.5 g kg(-1) (P<0.05). Broken-line regression model analysis relation on the basis of SGR, the optimal dietary arginine requirement could be 20.3 g kg(-1) in size I, and 17.9 g kg(-1) in size II of dry matter, respectively. The results may explain the adverse effects of a deficient or an excess dietary arginine level on growth and health of fish in future. Furthermore, the present study also suggests that an optimum dietary arginine could play an important role in improving growth, and maintaining health for different size of fish, which would be useful in developing amino acid balanced commercial feeds for blunt snout bream.