Effects Of Feeding Frequency On Growth Performance,Physiology And Biochemistry,and Liver Indexes Of Juvenile Siganus Canaliculatus

In the process of intensive farming,in order to pursue the maximum economic value of farmed fish,fishermen often take some measures when feeding fish,such as increasing the feeding amount and feeding frequency to speed up the growth of fish,and continuously increasing the breeding density to save aquaculture area,increase high protein or high fat content in feed to quickly increase fish nutrition and so on.This breeding mode not only causes the occurrence of fatty liver in fish,reduces the utilization of feed,but also increases the burden on the liver,resulting in a decline in immunity,resulting in an excessively strong response to external stress or even death.In recent years,during the breeding of Siganus canaliculatus,there has been a "black body" phenomenon at high feeding frequency,and caused a large number of deaths of farmed fish.Farmers usually reduce the feeding frequency to ensure that the fish pass through the "black body" period has achieved certain results.Therefore,taking the feeding frequency as the starting point,explore the four feeding frequencies of 1 time / d(F1),2 times / d(F2),3 times / d(F3),4 times / d(F4),to discuss the specific mechanism of the feeding frequency affecting the health status of the fish body,which can provide effective suggestions for production practice,improve the health status of the fish body while avoiding waste of feed,and improve economic efficiency.1.Effect of feeding frequency on the growth performance,physiology and biochemistry of S.canaliculatusIn this study,the growth data and shape data of S.canaliculatus under different feeding frequencies were recorded,combined with the analysis of serum indicators and body nutrients,and the growth performance and physiological and biochemical characteristics of the juvenile S.canaliculatus at different feeding frequencies were evaluated.The changes provide a scientific basis for optimizing the aquaculture technology of longfin basket fish.A.Growth indicators: The feeding frequency has a significant effect on the specific growth rate(SGR)of the experimental fish(P<0.05),and it increases with the feeding frequency.The feeding rate(FR),feed coefficient(FCR)and survival rate(SR)The F3 group showed the highest among the three indicators;the body weight and full length of the experimental fish groups in each group showed a significant upward trend with time over different feeding frequencies(P<0.05),and between the F3 and F4 groups There was no significant difference(P> 0.05);the weight gain(WG)of the F4 group did not show regular changes,and the F1,F2,and F3 groups showed a regular trend of increasing first and then decreasing with time.It shows that the feeding frequency of 3 times / d at this time can promote S.canaliculatus to reach the best state.B.Physical indicators: The feeding frequency has no significant effect on the viscera and spleen-body ratios of the experimental fish(P> 0.05).The liver-body ratio of the F4 group is significantly higher than that of the F1 group(P<0.05).Liver accumulation performance.C.Muscle nutrient composition: There is no significant difference in muscle body composition between the groups(P> 0.05).The total amount of saturated fatty acids and monounsaturated fatty acids in the muscle fatty acid content is significantly different between the groups(P<0.05),and The content of group F3 reached the highest level;the total content of polyunsaturated fatty acids in group F3 was second only to the content of group F1.It shows that the muscle nutrition of the F3 group is relatively rich,which is in line with the production benefits.D.Serum biochemical indicators: The activities of serum aspartate aminotransferase(AST)and alanine aminotransferase(ALT)in F3 group were significantly reduced(P<0.05),indicating that the liver function in F3 group was normal,and the activity of two enzymes in F4 group was significantly increased,indicating that this The liver cells in the group appeared damaged.Considering various indicators comprehensively,the feeding efficiency of S.canaliculatus under the feeding frequency of 3 times / d meets the actual production requirements.2.Effect of feeding frequency on liver index of S.canaliculatusThe purpose of this study was to investigate the occurrence of fatty liver in S.canaliculatus and the degree of damage to the liver caused by excessive intake of nutrients.A.Nutritional indicators: total saturated fatty acid content(SFA),monounsaturated fatty acid content(MUFA)and polyunsaturated fatty acid total(PUFA)in the liver have no significant difference between the F3 and F4 groups(P> 0.05);liver The total content of medium total amino acids(TAA),semi-essential amino acids(HEAA),essential amino acids(EAA)and non-essential amino acids(NEAA)were the highest in the F2 group(P<0.05),and the total amount of amino acids in the F3 and F4 groups was Significant downward trend(P<0.05).The total amino acid content only accounts for 60% of the F2 group.Amino acids can prevent fat accumulation in the liver and strengthen the immune system.Low amino acid content indicates poor liver health.B.Ultrastructure: The liver structure of the F1 group showed normal cell structure,the boundaries between the cells were obvious,the number of fat droplets in the liver was small,and the fat droplets in the liver cells of F2,F3 and F4 caused the nucleus to shift to the cell edge.In F3 and F4,a large number of large and dense fat droplets can be seen in the liver cells,some of which are even larger than the nucleus;the cytoplasm is lost;the cell boundaries near the end of the nucleus appear fuzzy,and the thickness of the cell membrane decreases.In this state,it can be seen that the liver cells of the F3 and F4 groups have the characteristics of fatty liver,and there is a certain degree of damage.C.Liver transcriptome: The differential gene expression of the three transcriptomes of the F1,F2 and F3 groups mainly focuses on lipid metabolism pathways,including the regulation of cholesterol synthesis,esterification and transportation,and high-density lipoprotein and very low-density lipoprotein particles.Remodeling,etc.,shows that as the frequency of feeding increases,the body's intake of nutrients increases and the body accelerates the storage and metabolism of nutrients;the differentially expressed genes in the F3 and F4 groups focus on immune-related functions,including classic complement activation Pathways and alternative pathways,the regulation of MHC I,interleukin and other immune-related factors,as well as inflammatory response and antigen binding,indicate that liver cell damage triggers the body's non-specific immunity.KEGG pathway annotation analysis There are no significant differentially expressed genes in the lipid synthesis and metabolism-related pathways in the F3 and F4 groups,but the genes in the immune-related pathways are significantly differentially expressed.It is speculated that the liver in the F4 group induces the body due to liver cell damage due to large amounts of fat deposition Immune response.Various detection indicators indicate that the 4 times / d feeding frequency seriously damages the liver of the fish,and the destruction of liver cells leads to a decline in the body's immune ability.This study shows that different feeding frequencies can significantly affect the growth and physiological and biochemical aspects of S.canaliculatus.Feeding 3 times / d shows excellent growth performance and good health,which is in line with production practice;while feeding frequency is at At 4 times / d,not only does it not significantly promote the growth of S.canaliculatus,but it will also cause damage to its liver,reflecting the contradiction between fish health and growth benefits.This study can reveal that the excessive feeding frequency caused not only this superficial problem of fatty liver of fish,but also a key problem related to the change of fish's own metabolism and immune function.There is a need for a deeper step Exploration and thinking.