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Study of Optimum Protein Requirements of Juvenile Black Sea Bream(Sparus Macrocephalus)

Author: WangLeiLei
Tutor: ShaoQingJun
School: Zhejiang University
Course: Animal Nutrition and Feed Science
Keywords: Juvenile black sea bream (Sparus macrocephalus) Dietary protein levels Growth performance Body compositions Digestive enzymes Biochemical parameters
CLC: S917.4
Type: Master's thesis
Year: 2007
Downloads: 12
Quote: 2
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Abstract

Protein is the dominating factor which affects fish growth and feed costs. Generally, enhancing the protein content in diet can increase the aquaculture output. However, if the protein content in diet is excess, it may cause waste of protein and the water quality may be destroyed by ammonia produced in the metabolism of amino acids. On the other hand, growth will be affected if the protein content in diet can not meet the aquatic animal nutritional requirement. Therefore, protein content in the diet must be suitable to guarantee the improvement of aquaculture output and to maintain an advisable cost.The experiments were conducted to study the influences of different dietary protein levels on growth performance, feed utilization efficiency, body compositions, digestive enzyme activities and biochemical indices of juvenile black sea bream (Sparus macrocephalus). The aims of this research was to deduce the optimum dietary protein level for juvenile black sea bream, so as to impel it grow rapidly and enhance the output and economic efficiency.The healthy black sea bream juveniles of the same batch were randomly allotted to six groups with triplicate of 20 fish (average body weight 16.64±0.16g). There were six experimental diets formulated to provide varying protein levels as follows: 31.95%,35.28%,38.53%,41.77%,45.15%and 48.53%. Fish were reared in tanks for 8 weeks with the diets aforementioned respectively. All the fish were killed to collect the carcass, plasma, liver, muscle, stomach, pylorus and intestine samples, and then analyzed the indices respectively.The growth trial suggested that the increased dietary protein levels could improve the growth of juvenile black sea bream and feed utilization. Weight gain rate (WGR), specific growth rate (SGR), general apparent digestibility of diet and apparent digestibility of nutrition ingredients such as protein, Ca and P changed consistently and increased with the increasing of dietary protein levels, which achieved the highest when the protein content was 41.77%, and inclined while the protein level was increased continually. On the contrary, the condition factor (CF), hepatosomatic index (HSI), feed conversion ratio (FCR) and protein efficiency ratio (PER) inclined with the increase of dietary protein levels, and so did apparent digestibility of lipid inclined in certain range.Fish body composition was significantly related to different dietary protein levels (P<0.05). The protein contents of whole fish, muscle and liver changed congruously with each other, which increased with the improving of dietary protein levels, and it achieved the highest when the protein content was 41.77%. Contrarily, in fixed range, the lipid of the tissue of juvenile black sea bream descended with the improving of dietary protein levels and decreasing of lipid content. The water content and crude ash in the tissue of juvenile black sea bream increased with the hoist of dietary protein levels, and the water content of whole fish and liver was observably related to the improvement of dietary protein levels (P<0.05), while the water content of muscle and crude ash content of tissues were not significantly related to it (P>0.05).The flesh quality, nutritional value and flavor of juvenile black sea bream muscle became better with the improving of dietary protein levels. The content of total amino acid, total essential amino acid and total flavor amino acid of juvenile black sea bream muscle increased with the improving of dietary protein levels, and the ratio of total essential amino acids to total amino acids also increased.Dietary protein levels had significant effects on digestive enzymes (P<0.05). At a certain range of protein levels, protease activity in the alimentary tract enhanced with the increasing dietary protein levels, which was the highest in stomach and reached the top level at 41.77%dietary protein level (protease activity in liver reached the top level at 45.22%), then decreased with continuously enhancing dietary protein levels. Lipase activity, the highest in foregut, and amylase activity which was the highest in liver, inclined with the dietary protein levels within certain range, and the two kinds of enzyme activity in middle protein teams (38.53%, 41.77%) was higher in each group compared to the other treatments.No significant correlation was found between glucose concentration and dietary protein levels (P>0.05). However, dietary protein levels had significant influences on triglycerides (TG), total cholesterol (T-CHO), glutamate pyruvate transaminase (GPT) and glutamete oxaloacetate transaminase (GOT) in plasma (P<0.05). The concentration of TG and T-CHO decreased with the increasing of dietary protein levels. GPT activity increased with the increasing of dietary protein levels; GOT activity reduced to the lowest levels at the dietary protein levels of 38.53%, then decreased. Enhancement of dietary protein levels could alleviate theliver burden and reduce the plasma lipids.Generally considering growth performance, feed efficiency and body compositions as the evaluating index, it has been concluded that when the water temperature is 28±1℃, the feasible dietary protein levels for black sea bream juvenile (wt 16-55g) is within the range of 38.53%to 41.77%, and the optimum level is 41.22%based on the best weight gain.

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