| Murray cod(Maccullochella peelii,Mitchell),native to Australia,is a highly valued freshwater farmed species.Murray cod is fresh and tender,and rich in nutrition,belongs to the famous special aquatic products.In recent years,due to the continuous improvement of people's economic level,some high-end aquatic products have also become more and more popular.The domestic demand for Murray cod,as a very distinctive high-quality fish,is increasing year by year,and has a very high breeding value and market potential.In nature,light always changes periodically following certain rules.Its changes can cause some internal physiological mechanisms in animals,and then regulate various life activities in their bodies.As an important environmental factor,light has an important impact on the growth and development of fish,feeding,swimming and other life activities,and how to use or eliminate this effect is of great value to improve fish artificial breeding technology.In the process of aquaculture,exploring the changes of light factors on the growth performance,muscle nutritional components,and stress response of Murray cod,and reasonable choice of lighting conditions have important theoretical guiding significance for the promotion of Murray cod production practice.This research is based on aquatic animal physioecological theory and research methods,and conducted three experiments with Murray cod as the research object in recirculating aquaculture system.Experiment 1 used two non-repeated experimental methods to explore the two factors of the recirculating aquaculture system: light intensity M(1200 lx,2400 lx,3600 lx)and photoperiod N(12L:12D,18L:6D,24L:0D)growth performance,physiological indexes and pressure response of juvenile Murray cod;Experiment 2 explored the effects of four different photoperiod(12L:12D,15L:9D,18L:6D,21L:3D)on the growth,muscle nutrition and breeding benefits of Murray cod;Experiment 3 explored the effects of four different light intensity(1200 lx,1500 lx,1800lx,natural light)on the growth,muscle nutrition and breeding benefits of Murray cod;The main experimental results are as follows:1.Effects of light intensity and photoperiod on growth performance,physiological indexes and stress response of juvenile Murray cod in recirculating aquaculture system.Under the light intensity of 1200 lx,the final weight,feed conversion efficiency and feed conversion ratio of Murray cod were significantly better than the 3600 lx light group(P <0.05);Different light intensity had a certain effect on the daily gain and survival rate of Murray cod,but no significance was observed(P <0.05);Under 18L:6D light condition,the feed conversion efficiency and feed conversion ratio of Murray cod were significantly better than the 24L:0D light group(P <0.05);However,different photoperiods did not significantly affect the final weight,daily gain and survival rate of Murray cod(P> 0.05);In the 18L:6D light group,the contents of ash and crude fat in Murray cod were the highest,and were significantly higher than those in the 24L:0 D and 12L:12D light groups(P> 0.05).However,different light intensity had no significant effect on the nutritional composition of Murray cod(P> 0.05).In addition,under the light intensity of 1200 lx,the total protein(TP)and globulin(GLB)contents in serum were significantly higher than those in other groups(P<0.05).In contrast,the levels of urea nitrogen(BUN)and superoxide dismutase(SOD)in serum were significantly affected by the photoperiod(P <0.05).No significant difference was found in other indicators in serum(triglycerides,albumin,cortisol,etc.)(P> 0.05).2.Effects of different photoperiod on growth,muscle nutrition and aquaculture benefits of Murray cod in recirculating aquaculture system.Under 15L:9D light conditions,the final weight,daily gain and specific growth rate of Murray cod were significantly higher than those of the other three groups(P <0.05),while the 21L:3D experimental group was significantly lower than the other three groups(P <0.05));The content of crude fat in the muscles of Murray cod in the 15L:9D light group was the highest,and the content of crude fat in the muscles of Murray cod in the 21L:3D light group was the lowest and significantly lower than that in the 12L:12D and 15L:9D light groups(P <0.05);In addition,under 15L:9D light conditions,the total amount of threonine,glutamic acid,valine,tyrosine,lysine,amino acids and total essential amino acids in Murray cod muscle reached the maximum and significantly higher than 18L:6D light group(P <0.05);Under 12L:12D light conditions,the glycine,alanine,leucine,and non-essential amino acids in Murray cod muscle reached their maximum values,and the total amount of glycine and non-essential amino acids was significantly higher than the 18L:6D and 21L:3D light groups(P <0.05);The total cost required by the 15L:9D light group is the highest,but the total revenue,total net benefit,and benefit-cost ratio are significantly higher than those of the other experimental groups(P <0.05).The cost required by the 21L:3D light group is the lowest,but the total benefit,the total net income and benefit-cost ratio were significantly lower than those of other experimental groups(P <0.05).3.Effects of different light intensities on the growth,muscle nutrition and breeding benefits of Murray cod in recirculating aquaculture system.Under 1500 lx light conditions,the final weight,daily weight gain and specific growth rate of Murray cod were significantly higher than those of the other three groups(P <0.05),while the 1200 lx and natural light groups were significantly lower than the other two groups(P <0.05).The ash and crude fat content in Murray cod muscle of the 1500 lx light group were significantly higher than those of the other three groups(P <0.05);The contents of water and crude protein in the muscle of codfish in the natural light group were significantly higher than those in the other groups(P <0.05);In addition,aspartic acid,threonine,glutamic acid,alanine,valine,methionine,isoleucine,leucine,leucine,Phenylalanine,histidine,lysine,arginine,total amino acids,total essential amino acids and non-essential amino acids all reached the maximum and significantly higher than the 1500 lx light group(P <0.05);In the 1500 lx group,despite the highest input cost,due to the fast growth rate,its total benefits,total net benefits,and benefit-cost ratios were significantly higher than those of the other experimental groups(P <0.05),while the natural light group had the least input cost,but its total benefits The total net income and the cost-benefit ratio were significantly lower than those of the other experimental groups(P <0.05).In summary,the experimental results show that the photoperiod and light intensity have significant effects on the growth,muscle nutritional composition,amino acid composition,and physiological indicators of Murray cod.In the breeding process of recirculating aquaculture system,the scientific and reasonable use of artificial lighting is of great significance for improving aquaculture technology,improving the breeding environment,and increasing breeding income. |
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