PHYSIOLOGICAL DIFFERENCES IN THE ORGANS OF DIFFERENT GROWTH PERFORMANCE SUBGROUPS WITHIN THE SAME COHORT OF LARGE YELLOW CROAKER(LARIMICHTHYS CROCEA)JUVENILES
Investigating the primary causes of physiological differences in the organs among subgroups with different growth performance within the same cohort of large yellow croaker juveniles can reveal the underlying logic of survival adaptation strategies and differentiation in weight gain mechanisms.This has great practical significance for the selection of high-quality breeding and release groups of large yellow croaker juveniles,and it guides more scientific and efficient aquaculture practices for large yellow croaker.3 000 large yellow croaker juveniles,which were cultured in cage nets for 3 months,were randomly caught from the Xiangshan Xihu Harbor area in Ningbo City.After fasting for 2 days,they were divided into five subgroups(A,B,C,D,E)based on body weight from largest to smallest.The subgroups had the following characteristics:A[body weight(3.45±0.43)g,occurrence rate 5％],B[body weight(2.60±0.18)g,occurrence rate 20％],C[body weight(2.00±0.21)g,occurrence rate 50％],D[body weight(3.45±0.23)g,occurrence rate 20％],E[body weight(0.74±0.04)g,occurrence rate 5％].A systematic study was conducted on the differences in oxygen consumption rate,asphyxiation point,and activities of enzymes related to visceral and gill tissue functions among different growth performance subgroups,based on the measurement and statistical analysis of organ proportion traits,including the gill coefficient,viscus coefficient,gill-viscus ratio,gill net weight ratio,and viscus net weight ratio.The study found:(1)Significantly high values of gill coefficient,viscus coefficient,and average daily oxygen consumption rate(P＜0.05)can lead to a significant decline in growth performance of large yellow croaker juveniles;(2)Differentiation in diurnal rhythm of oxygen consumption is the main cause for significant changes in growth performance,specifically,subgroups A and B had significantly higher average daytime oxygen consumption rates than average nighttime rates(P＜0.05),while subgroup E had no significant difference between average daily,daytime,and nighttime oxygen consumption rates(P＜0.05);(3)Clustering of oxygen consumption rate and organ proportion traits proved effective in identifying subgroups C and E;(4)As the oxygen content in the water at the asphyxiation point increases,the growth performance of large yellow croaker juveniles will show a very obvious weakening effect,with only subgroups A and B showing significant differences in oxygen content in the water at the asphyxiation point compared to subgroup E(P＜0.05),and the trend being E＞A≈B;(5)Among the digestive enzymes in the viscera and phosphatases,the enzyme activities most in line with the order of growth performance of large yellow croaker juveniles were amylase and AKP,with the former showing a trend of increase with enhanced growth performance,and the latter showing A＜B＜C＜D＜E(P＜0.05);among ATPases,Ca2+/Mg2+-ATPase enzyme activity showed no significant differences between groups(P＞0.05),while Na+/K+-ATPase enzyme activity was significantly higher in subgroup A compared to subgroups D and E(P＜0.05),with no significant differences among other subgroups(P＞0.05);(6)Among gill SOD,CAT,and POD,the enzyme activities most in line with the order of growth performance of large yellow croaker juveniles were SOD,which showed A＞B＞C≈D≈E,and Na+/K+-ATPase and Ca2+/Mg2+-ATPase enzyme activities both showed A＞B≈C＞D≈E.This research can provide a scientific basis for the construction of a large yellow croaker growth performance evaluation system and inform the selection and breeding of fast-growing strains.
large yellow croaker juvenilesgillvisceragrowth performanceoxygen consumption rateasphyxiation pointenzyme activity
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