Studies On Protein And Lipid Requirement By Triangular Bream(Megalobrama Terminalis)

Triangular bream（Megalobrama terminalis）is an omnivorous freshwater fish that has many excellent properties,such as rapid growth,high disease resistance and good taste.Recently,the triangular bream has become an important Chinese commercial species,but there are few knowledge about their nutrient requirements.There are two parts in this paper,one for protein requirement and another for lipid requirement.The main results are as follows:1.A 10-week feeding trial was conducted to determine the dietary protein requirement of juvenile triangular bream.Five semi-purified diets were formulated with varying crude protein（CP）levels（ranging from 26.30 to 50.09%）,each diet was given to triplicate groups（20 fish per group,1.30 g per fish）.The results of feeding trial showed that the weight gain（WG）,specific growth rate（SGR）and feed efficiency（FE）were enhanced by increasing dietary protein level up to 44.18%,but there were no significant differences for protein levels from 44.18%to 50.09%.The protein efficiency ratio（PER）and daily feed intake（DFI）showed a decreased trend with increasing dietary CP levels.In this study,the viscerosomatic index（VSI）and hepatosomatic index（HSI）were not significantly affected by the different treatments,while the intraperitoneal fat ratio（IPF）increased significantly with decrease in CP levels.The highest lipid retention value（153.89%）and liver glycogen value were observed in fish fed the lowest CP diet.In this study,the highest triglycerides level in plasma was observed in fish fed diets with the lowest CP level.Base on the WG and FE,the optimum dietary protein level for M.terminalis was suggested to be 44.18%.2.Five diets with different lipid sources,including fish oil（FO）,soybean oil（SO）,linseed oil（LO）,rapeseed oil（RO）and palm oil（PO）,were fed to juvenile Triangular Bream Megalobrama terminalis（initially weighing,1.20±0.02 g）for 70 days.At the end of the feeding trial,weight gain（WG）,specific growth rate（SGR）,feed conversion ratio（FCR）,and daily feed intake（DFI）were not significantly different among all treatments.The retention rates of DHA(C_22:6n-3)in fish fed LO-based（143.76%）diets were significantly higher than those fed FO-based（61.01%）diet.Moreover,fish fed LO-based diet showed a significantly higher EPA（C20:5n-3）content（1.63%）in the liver than fish fed SO,RO and PO-based（1.07,0.89 and 0.94%,respectively）diets.The retention rates of ARA(C_20:4n-6)in fish fed RO-based（341.30%）diets were significantly higher than those fed FO,LO and PO-based（87.35,176.83 and 216.37%,respectively）diets,while fish fed SO and RO-based diets showed significantly higher ARA contents in the liver compared to fish fed FO-based diet.The fatty acid compositions of fish tissues were significantly affected by different lipid sources.Compared with FO group（18.44%）,fish fed VO diets showed lower n-3 LC-PUFA contents in dorsal muscles and significant differences were detected in fish fed SO（10.12%）and RO（10.94%）diets.These results showed that Triangular Bream have an ability to synthesize DHA,EPA and ARA from ALA(C_18:3n-3)and LA(C_18:2n-6).However,fish fed VO-based diets could reduce the nutritional value of fish flesh.