ALBERT

Notes: Two experiments (I and II) were conducted to evaluate the effect of nonprotein phenolic amino acid, L-dopa (L-3,4-dihydroxyphenylalanine) on growth, metabolism and feed assimilation of common carp. Six isonitrogenous and isoenergetic diets (diets 1–6 containing 0, 2.5, 7.0, 14, 28 and 56 g kg–1L-dopa, respectively) were prepared by replacing wheat meal in the feed with L-dopa. For experiment I (8-week duration), each treatment had two replicates with five fish each per replicate (mean initial body mass of 13.4 ± 1.0 g), whereas five groups of carp, each consisting of three fish, individually kept in respiration chambers, giving three replicates per treatment with a mean body mass of 25.0 ± 1.8 g were used for experiment II (4-week duration). Fish were fed six times their maintenance ration daily (3.2 g feed kg–0.8 day–1). No fish died during either experiment. In experiment I, the growth rate, feed conversion ratio (FCR), protein efficiency ratio (PER) and apparent net protein utilization (ANPU) of carp fed diets 1, 2 and 3 were similar but they were significantly (P 〈 0.05) higher than those in dietary groups 4, 5 and 6. However, no significant differences were observed with regard to body composition (moisture, protein, lipid, ash and energy contents) between control (1) and the diets 2, 3, 4 and 5. Fish fed diet 6 had reduced lipid and energy contents (P 〈 0.05) when compared with other dietary groups. In experiment II, L-dopa significantly increased the oxygen consumption per unit body weight gain in treatments 4, 5 and 6. The average metabolic rate also tended to be higher in these groups. The energy expenditure was similar in treatment groups, but the energy retention was significantly lower and energy dissipated significantly higher in dietary groups 4, 5 and 6. The cholesterol level in blood plasma between the control and L-dopa containing diets was not significantly different. It may be concluded that at higher inclusion rates (〉7 g kg–1) L-dopa appears to be a major antinutrient and hence the protein sources of plant origin, containing high amounts of L-dopa (i.e. mucuna beans) should be used with caution as fish meal substitutes in carp diets.