| Swimming is one of the most important activities in fish.The intensities of swimming exercise in fish will change with their physiological and external conditions.The metabolisms of matter and energy of fish will produce the physiological response in the different swimming velocity and duration of exercise training.Meanwhile,nutrient level also has an important influence on the metabolism of fish in food.The materials of protein and carbohydrate of are an important feed of nutrient and energy in fish,the growth and efficiency of feed conversion in fish will be influenced by materials of the content and its proportion,which will largely impact on the cost of feed and aquaculture.Therefore,energy and nutrient metabolism and nutritional requirements of fish subjected to exercise training will help to further understand the relationship between fish physiology and nutritional metabolism and its related mechanisms,developing efficient nutritional feed is suitable for exercise aquaculture of flowing water to provide guidance in practiceIn present study,the metabolisms of protein and carbohydrate and different dietary protein levels in Nile tilapia(Oreochromis niloticus),an important cultured fish in China,subjected to swimming training were studied to assess if exercise training can improve carbohydrate metabolism and reduce the consumption of protein.In order to determining optimal intensity and duration of exercise training in Nile tilapia.Basing on the experimental results mentioned above,it is examined the possibility that sustained swimming exercise training and appropriate lower dietary protein levels can maintain or improve at the growth and efficiency of feed and nutritional utilization in Nile tilapia1.The metabolism of protein and carbohydrate in Nile tilapia subjected to exercise trainingTwo experimental periods,2 weeks and 6 weeks,and four water flow velocities,0.0 bl/s,1.0 bl/s,1.5 bl/s and 2.0 bl/s were set.The fish got 12 h of swimming training,and were fed with commercial fish pellets three times per day.The body morphologies,growth,body compositions,enzyme activities and the expression of genes related to protein and carbohydrate metabolism were examinedThe main results were as follows:the activities of enzymes related to protein metabolism in the muscles and livers,cathepsin-D(CTS-D),adenosine deaminase(ADA)and glutamate dehydrogenase(GDH),etc of fish in 1.0 bl/s and 1.5 bl/s groups trained for 6 weeks were significantly lower than those trained for 2 weeks(P<0.05);trained for 2 weeks,the activities of CTS-D,alanine amino transaminase(ALT),aspartate amino transaminase(AST),ADA and GDH of fish in 1.5 bl/s groups were significantly lower than the other groups(P<0.05);the activities of protein metabolism enzymes in the muscles and liver of fish in 1.0 bl/s and 1.5 bl/s groups trained for 6 weeks were significantly lower than those of the other groups(P>0.05);the activities of carbohydrate metabolism enzymes,glucose kinase(GK)and 6-phosphoric acid fructose kinase-1(PFK-1),in the red muscles and livers of fish in 1.0 bl/s and 1.5 bl/s groups trained for 6 weeks were significantly higher than those trained for 2 weeks(P<0.05);trained for 2 weeks,the activities of GK,hexokinase(HK),PFK and pyruvate kinase(PK)of the fish in 1.5 bl/s were significantly higher than those in 2.0 bl/s and the control group(P<0.05);trained for 6 weeks,the activities of carbohydrate metabolism enzymes in the red muscles and livers of the fish in 1.0 bl/s and 1.5 bl/s groups were significantly higher than those of the other groups(P<0.05);and the genes of glutamate dehydrogenase(GDH)and glucose gene(GK)were expressed in all organizations of the fish body,and exercise training can decrease the expression levels of GDH and increase the GK expression levels.The research results show that appropriate flow velocities and long-term training can significantly reduce consumption of proteins and improve on carbohydrate utilization of tilapia.Appropriate exercise training promoted the growth of the fish and greatly improved the nutrition composition:the contents of free amino acid(FAA)and crude protein(CP)in the muscles and livers of the fish in 1.0 bl/s and 1.5 bl/s groups trained for 6 weeks were significantly higher than those trained for 2 weeks(P<0.05);trained for 2 weeks,the contents of CP and FAA in the muscles and livers of the fish in 1.5 bl/s group were significantly higher than those in the other groups(P<0.05);trained for 6 weeks,the contents of CP and FAA in the muscles and livers of the fish in 1.0 bl/s and 1.5 bl/s groups were significantly higher than those in the other groups(P>0.05);the contents of glycogen(Gly)and nitrogen free extract(NFE)in the muscles and livers of fish in 1.0 bl/s and 1.5 bl/s groups trained for 6 weeks were significantly less than those trained for 2 weeks(P<0.05);trained for 2 weeks,the contents of Gly and NFE in the muscles and livers of fish in 1.5 bl/s group were significantly lower than those in the other three groups(P<0.05);and trained for 6 weeks,the contents of Gly and NFE in the muscles and livers of fish in 1.0 bl/s and 1.5 bl/s groups were significantly lower than those in the other groups(P>0.05).2.The effects of dietary protein level(protein to energy ratio)and exercise training on the growth and the efficiency of feed and nutrition conversion in Nile tilapiaBasing on the experimental results mentioned above,two flow velocities,0.0 bl/s and 1.5 bl/s,and 6 dietary protein levels,15%(D1),20%(D2),25%(D3),30%(D4),35%(D5),and 40%(D6),whose ratios of protein to energy were 10.58,14.26,17.02,19.89,and25.37,respectively,were set.The fish got 12 h of swimming training and were fed with commercial fish pellets three times per day.The fish growth,nitrogen budget,energy budget,body compositions,feed efficiency and liver tissue morphology,the activities of enzymes and the expressions of genes related to protein and carbohydrate metabolisms were measuredThe main results were as follows:with the increase of feed dietary protein level(protein to energy ratios),feed intake(FI),protein digestibility of the feed(ADCP)and energy digestibility of the feed(ADCE)performance were ascend in the low ratios and descend in the high ratios,and D3 had the highest indexes;FI,ADCP and ADCE of exercise groups were significantly higher than those of the control group in the same protein level(P<0.05);feed conversion efficiency(FCR),protein efficiency ratio(PER),protein production value(PPV),and protein growth ratio(PGR)increased first and then decreased with the increase of feed protein contents,and those in D3 were the highest;FCR,PER,PPV and PGR in exercise groups were significantly higher than those in the control in the same protein level(P<0.05);with the increase of feed protein contents,the expressions of GDH,the gene related to protein metabolism related,in red muscles and livers decreased,but those of GK,the gene related to carbohydrate metabolism,in red muscles and livers increased;in the same protein levels,the expression of GK in the exercise group was significantly higher than that in the control(P<0.05),while the GDH expression had the opposite trend(P<0.05);with the increase of feed protein to energy ratios,the nitrogen intake or consume energy for growth decreased,but the proportion of excrete nitrogen(energy)increased;in the same protein levels,exercise training can improve the nitrogen and energy and reduce the excreted nitrogen(energy);weight gain rate(WG)and specific growth rate(SGR)showed the trend of rising first then downward with the increase of dietary protein levels,and D3 had the highest WG and SGR;in the same protein levels,the WG and SGR of fish in the exercise groups were significantly higher than those of the control(P<0.05);The contents of CP and FAA in the muscles and livers increased first and then decreased with the increase of feed protein contents,and those in D3 were the highest;in the same protein levels,the contents of CP and FAA in exercise groups were obviously higher than those of the control(P<0.05);and fish in D3 had the lowest Gly and NFE contents in the red muscles and liversThe results showed that sustained swimming exercise training and the suitable crude protein level,such as 25%,can improve the feed conversions and nutrient efficiency of tilapia,promote growth,raise the contents of CP and FAA,and increase the nutritional and economic values of the fish. |
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