| Summary: | 碩士 === 國立海洋大學 === 水產食品科學研究所 === 83 === A series of two experiments were conducted to study the optimum dietary protein level and the protein to energy ratio of groupers, Epinephelus malabaricus.
Experiment I: Eight isoenergetic pruified diets ranging from 0% to 56% protein in 8% increements were fed for 8 weeks to triplicate groups of grouper (average initial weight: 9.22±0.11 g) in a cosed recirculation system. The water temperature was 28-30℃ and salinity was 29-32 ppt. Weight gain and protein gain of fish were proportional to the protein content of the diet up to an incorporation rate of 48%. Feed conversion ratio (FCR) decreased with increasing dietary protein level, and 48% protein diet was the lowest. Net protein utilization (NPU) and biological value (BV) both decreased with increasing dietary protein level. Protein digestibility was the highest in the 48% protein diet and the lowest in the 8% protein diet. Lipid digestibility was not affected by dietary protein level. The fish fed the 56% protein died had the highest body protein and lipid contents, and the lowest body moisture content. The dietary protein level that yielded maximum growth in Epinephelus malabaricus was 51.2% based on a broken-line model estimation of the weight gain.
Experiment II: Two dietary protein levels (50% and 44%) were used along with four energy levels at each protein level (305, 340, 375 and 410 kcal/100g diet). The experimental diets were fed for 8 weeks to triplicate groups of grouper (average initial weight：10.70±0.14 g) in a closed recirculation system. The water temperature was 25-27℃ and salinity was 29-32 ppt. Weight gain of fish was not significantly (0＞0.05)different when 50% protein diet was fed. However, weight gain of fish improved at the dietary energy levels of 340─375 ckal/100g when 44% protein diet was incorporated. Protein and lipid digestibilities were not affected by the dietary protein and enegry levels. At each dietary protein level, carbohydrate digestibility decreased with increasing dietary energy level. The fish fed with 410 kcal/100g diet had lower body protein retention, protein content, and higher body lipid content. Both hepatic glutamate dehydrogenase and glutamate-pyruvatetransaminase activities decreased with increasing dietary energy level. The glutamate dehydrogenase had the highest specific activity. The amino acid contents for grouper carcasses were similar in all the dietary groups. Based on the polynomial regression estimation, maximum growth of groups wea reached when dietary energy was 324.7 kcal/100g diet at the 50% dietary protein level and when dietary energy was 337.0 kcal/100g diet at the 44% dietary protein level. These data suggest that when the energy level of the diet maintain at 340─375 kcal/100g diet, the dietary protein level for grouper can be owed from 50% to 44%.
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