LOWERING DIETARY PROTEIN LEVELS IN THE DIETS OF JIAN CARP Cyprinus carpio var. Jian USING SUPPLEMENTAL AMINO ACIDS

Jian carp is a variant of the common carp, Cyprinus carpio. This strain of common carp is widely farmed in China, accounting for ~50% of the total annual production of farmed common carp. Practical diets of Jian carp often contain high levels of crude protein (CP). Dietary protein levels and sources largely determine the feed cost. Supplemental amino acids in the diets, formulated following ideal protein concept, provide an opportunity to utilize plant protein sources more efficiency as well as minimize excess levels of dietary protein. The present study was conducted to investigate the effects of essential amino acids (EAA) supplementation on the success of dietary protein reduction for Jian cap.

A 10-week feeding trial was conducted in 20 floating cages (1m×1m×1m) with juvenile (initial body weight 8.4g) Jian carp at 30 fish per cage. Five iso-energetic (17.5MJ/kg gross energy) diets were formulated including a positive control (D1, 37.84 % CP), a negative control (D5, 28.98 % CP), and three test diets (D2-D4, 34.03-29.90 % CP). Fishmeal, soybean meal, rapeseed meal and cottonseed meal were used as main protein sources. Crystalline amino acids were added in D2-D4 to meet the requirement data published, considering the recommendations generated by Evonik Nutrition and Care GmbH (Germany). Negative control (D5) diet was not balanced for EAA using supplemental sources, resulting in lower levels of several EAA including Met, Lys, Thr, Trp, Iso and His relative to other diets. Water temperature was maintained at 28-32°C and dissolved oxygen was about 5.5mg/L. Natural photoperiod (light-dark cycle) was maintained throughout the whole experiment period.

There was no differences in growth performance of fish fed decreased levels dietary protein (D1-D4) balanced for EAA, whereas feeding the negative control diet (D5) resulted in significantly lower performance compared with the other diets (Table 1). Total ammonia nitrogen excretion (TAN) decreased with the decreasing dietary protein, with D4 (29.9% CP) showing significantly lower levels (25% less) of excretion relative to D1 (37.84% CP). Dietary treatments did not affect whole-body composition, but influenced protein and most EAAs retentions. The present study clearly demonstrated that crystalline amino acids supplementation to balance EAAs is the key to maintain growth performance, feed utilization as well as improve protein and amino acids retention of juvenile Jian carp, when dietary protein could be reduced from 37.84 % to 29.9 %. The advantage of such strategy is sparing expensive protein resources, reducing feed cost as well as minimizing environmental impact, and overall benefiting for economic and sustainable production of Jian carp.