| Trachonotus Ovatus is a warm water fish with rapid growth and high economic value.It has become one of the main marine culture species in southern China.Salinity is one of the environmental factors that have a greater impact on the survival and growth of marine fish.Because extreme weather such as continuous rainfall and typhoon often leads to changes in the salinity of the cultured area,which will seriously affect the growth and survival of T.ovatus in this long-term environment,causing huge losses to its breeding industry.Feeding frequency is one of the important factors affecting feeding and feed conversion efficiency.Reasonable feeding frequency could not only improve fish growth and survival,unreasonable feeding frequency may not meet the needs of fish survival and growth.The supply of food may also increase the cost of farming and undermine the farming environment.Therefore,the daily management of the spawning pompanos is particularly important in the breeding process,especially the changes in the aquaculture environment and and the frequency of feeding.In this paper,we determined the optimum growth salinity and feeding frequency of T.ovatus by measuring the growth performance,muscle quality,physiological and biochemical indexes,and changes of intestinal microbial composition of T.ovatus under different culture salinities,which provided a theoretical basis for the healthy breeding of T.ovatus.The main findings of this paper are as follows:1.Effects of salinities on growth,physiology and intestinal microbiota of Trachinotus ovatusThe aim of this study was to investigate the appropriate salinity of T.ovatus,and to provide a scientific theoretical basis for its healthy farming and quality improvement.The mean body weight of the experimental fish was 12.07±0.13 g.Firstly,the final body weights,survival rate,specific growth rates,feed conversion ratio,muscle nutritional composition and flesh quality of T.ovatus,which had been reared at salinities 5‰,15‰,25‰and 35‰for 56 days,were investigated.Firstly,The results showed T.ovatus grew well and the survival rate was 100%among 5‰,15‰,25‰and 35‰salinities.However,T.ovatus reared at 15‰salinity grew significantly faster than those reared at the other salinities?P<0.05?.The specific growth rate at 15‰was higher than at 5‰?P<0.05?,which the feed conversion ratio was higher than at 5‰?P>0.05?.There was no difference in fatness and visceral ratio between the salinity groups?P>0.05?,and the liver-to-body ratio of 15‰salinity was significantly lower than that of the other three salinity groups?P<0.05?.There was T.ovatus reared at 25‰salinity significantly different in the crude protein content of muscle at 35‰?P<0.05?.There were no significant differences in moisture,ash and crude fat content in salinity treatment groups?P>0.05?.The drip loss rate and cooking loss rate of T.ovatus at 5‰were significantly higher than the other three salinity groups?P<0.05?.There were no significant differences in muscle hardness and springness?P>0.05?.It is indicated that proper reduction of salinity can improve the growth and muscle quality of T.ovatus,the suitable culture has a salinity range of 15-25‰according to the present results.Secondly,the levels of branchial NKA activity showed a typical‘U-shaped'pattern with the lowest level at 15‰salinity,which suggested a lower energy expenditure on osmoregulation at this level of salinity.Our study showed that osmolality increased significantly as the salinity increased.No significant differences in triglyceride,total protein,albumin,glucose,lactate,malondialdehyde,lysozyme,phosphofructokinase aldose reductase and triiodothyronine were detected among the salinity treatments.Salinity had a differential effect on cholesterol,alanine aminotransferase,aspartate aminotransferase,glucose 6-phosphate dehydrogenase,cortisol and thyroxine,and was higher in the salinity 5‰.The results of this study showed that the cholesterol and alanine aminotransferase,aspartate aminotransferase and cortisol of juveniles at 5‰were higher than those of other salinity groups.Our results showed that glucose 6-phosphatedehydrogenase significantly increased at 5‰and 35‰salinity.T4 content level increased with the increase of salinity,and there was a significant difference between the groups?P<0.05?.The cortisol content decreased first and then increased with the increase of salinity,and there was a significant difference between the groups.Finally,the 16s rDNA high-throughput sequencing technology was used to explore the effects of different culture salinity on the intestinal microbiota.Salinity is one of the most important environmental factors influencing the intestinal microbiota.The aim of this study was to investigate the intestinal microbiota of juvenile golden pompano reared at different salinities.Based on ACE,Chao1 and Shannon,Simpson diversity indices,salinity did not influence the bacterial richness and diversity in golden pompano intestine.The data indicated that the dominant phyla in golden pompano intestine reared at each salinity group were Proteobacteria.The principal coordinates analysis?PCoA?indicated that the bacterial communities were not clustered,and the bacterial communities were very different in the salinity groups.The findings showed that golden pompano have specific intestinal microbiota in different salinity environments.Further studies are needed to explore the relationship between the intestinal microbiota and growth of golden pompano under different salinities.2.Effects of feeding frequency on growth,physiology and anti-low salinity stress of Trachinotus ovatusIn order to investigate the effect of feeding frequency on growth performance,biochemical indices,muscle composition and anti-low salinity stress of T.ovatus.The mean body weight of the experimental fish was 25.81±0.15g.Six groups of feeding frequency were designed?1,2,3,4,5 and 6 times/day?for 10 weeks and carried out a 3hours low salinity 4‰stress test to analyze the survival rate of T.ovatus.The results showed that final body weight,weight gain rate,specific growth rate,viscerosomatic index and hepatosomatic index of 4 times/d were significantly higher than other groups?P<0.05?.However,there was no difference for survival rate and feed conversion ratio in the group?P>0.05?.They had an effect on total protein,total cholesterol,low-density lipoprotein and high-density lipoprotein content,and they was lowest at 4 times/d.The crude fat and crude protein content were higher at 4 times/d,but there was no difference in water and ash between the groups?P>0.05?.Superoxide dismutase,catalase and total antioxidant capacity were significantly higher at the 3 times/d and 4 times/d groups than in the other groups?P<0.05?,there were no significant difference between the other groups?P>0.05?.Malondialdehyde was significantly higher at the 4 times/d group than in the 1,2,5 times/d group?P<0.05?,but there was no significant difference between the other groups?P>0.05?.Lysozyme was significantly lower in the 1 times/d group and the 6 times/d group than in the other groups?P<0.05?,and there was no significant difference between the other feeding groups?P>0.05?.The survival rate was the highest at 4 times/d in anti-low salinity stress.According to the results of this experiment,there were fast and healthy growth,maintaining muscle quality in fish and strong resistance to low salt stress at 4 times/d.The suitable feeding frequency of T.ovatus was 4 times/d. |
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