Effects of dietary protein level on growth performance and body composition of rock porgy

Abstract

The study aims to quantify the dietary optimum protein levels and body composition for rock porgy. Experiment diets with five protein levels (35%, 40%, 45%, 50% and 55%) were each fed to triplicate groups of rock porgy (mean initial weight: 8.00±0.02g) in a recirculating rearing system for 8 weeks. The results showed as dietary protein levels increased, weight gain (WG), feed conversion ratio (FCR) and specific growth rate (SGR) were improved. WG were highest (p<0.05) in fish fed diets with 50% and 55% protein than those fed with the diets of 35% and 40% protein. However, no significant difference (p>0.05) was observed in the fish fed with the diet of 45% protein. The results of FCR and SGR had the same tendency with WG. However, protein efficiency ratio was negatively correlated to dietary protein levels. Estimation using a broken-line model, based on body weight gain and dietary protein requirement, the optimum protein level was 50.42% for maximal growth. No significant differences were found in condition factor and viscerosomatic index among dietary treatments. Hepatosomatic index decreased with the increasing dietary protein levels.本研究探討條石鯛幼魚之最適蛋白質需求以及不同含量之蛋白質飼料對成長和體組成的影響。實驗飼料共分為5組，蛋白含量分別為35%、40%、45%、50%及 55%。魚隻初重 8.00±0.02g，流水式養殖，實驗進行八週。結果顯示飼料中蛋白質含量增加，體增重率(WG)、飼料轉換率(FCR)與絕對成長率(SGR)越佳；50%和55%組 WG(952-955%)最高且顯著高於35%及40%組(p<0.05)，但與45%組無顯著差異(p>0.05)。FCR及 SGR 呈現與WG相似的趨勢，蛋白質效率(PER)則隨蛋白質含量增加而下降。WG及飼料蛋白質含量進行拐點法(Broken line)分析，求得最適蛋白質含量為 50.42%。肥滿度與內臟體比各處理組間無顯著差異；肝體比有隨蛋白質含量增加而下降之趨勢。