Effects Of Low Salinity And Biofloc Technology System On The Growth,Serum Biochemical Indices,Digestive Enzymes And Non-specific Immune Enzymes Of Maccullochella Peelii Peelii

At present,Macullochella peelii peelii has been widely concerned as one of the important high-quality special fish in China,because of high nutritional value and ornamental value.Like most of Australia's freshwater fish,the ancestors of Macullochella peelii peelii stripes come from the ocean.Salinity,as an important physical and chemical factor in aquaculture environment,is closely related to various indicators of cultured animals.At present,there is no experiment on salinity of Macullochella peelii peelii.At present,most of the cultivation of Macullochella peelii peelii at home and abroad adopts the circulating water system.Compared with the circulating water culture technology,the biofloc culture system has the advantages of simpler equipment composition and lower cost.At present,it has a good breeding effect on a variety of aquatic animals,which is favored by the majority of farmers,and the cultivation of carnivorous fish also has a certain improvement effect.As a carnivorous animal with good taste and high nutritional value,it is also of great research value whether it can grow and survive well in the biofloc system.Therefore,this paper studies the effects of low salinity and biofloc system on the growth,physiology and biochemistry of Maccullochella peelii peelii.The experimental design is divided into three parts as follows:1. Effects of low salinity on the growth performance,serum biochemical indices and non-specific immunity of Maccullochella peelii peeliiAfter salinity acclimation,the effects of different salinity(0,3,6,9)on the growth performance,serum biochemical indices and non-specific immunity of Maccullochella peelii peelii were studied within the 60 days of experiment period.The results showed that the final body weight was significantly decreased with the increasing salinity(P<0.05).Additionally,the feed conversion ratio attained an optimum value when the salinity was 0(1.11±0.11),and the survival rate was the highest when the salinity was 3(98.33%±2.89%).The serum indices showed that creatinine levels followed a decreasing trend with the increasing salinity.Urea nitrogen content increased with the increasing salinity levels,i.e in the salinity 9(7.00±0.26 mmol/L)it was significantly higher than that of group 0(P<0.05).Notably,there were no significant differences in other indicators evaluated.The activities of non-specific immune enzymes were significantly affected by the salinity.The activities of alkaline phosphatase and lysozyme were highest when the salinity was 3.Also,the activity of superoxide dismutase was highest when the salinity was 6,which was significantly higher than that in other groups.The catalase activities of group 0 and 6 were significantly higher than that in other groups.In summary,the water salinity level of 3 was found to be suitable for the cultivation of Maccullochella peelii peelii.2. Effect of mixed suspended solids concentration in BFT system on the culture of Maccullochella peelii peeliiThe effects of different mixed suspended solids concentrations(group L:150±25mg/L,group M:300±25 mg/L,group H:450±25 mg/L)on the water quality,the growth performance,serum biochemical indices,digestive enzymes and non-specific immunity of Maccullochella peelii peelii were studied during the 60-days of experiment period.The results showed that the changes of the water quality of Maccullochella peelii peelii cultured with different mixed suspension solids were within a reasonable range.At the same time,the ammonia nitrogen concentration of group H>group M>group L;the fluctuation of nitrite concentration was higher overall;the changes of nitrate and phosphate concentrations were consistent,and the three groups gradually accumulated and increased significantly with the cultivation time(P<0.05).The final body weight,average daily weight gain,weight gain rate,visceral volume ratio,hepatopancreas ratio and specific growth rate of Maccullochella peelii peelii terminal body under different mixed suspended solids were the highest in group M and the lowest in group L,and the difference was significant(P<0.05);but the daily feeding rate and feed conversion ratio in group M were significantly lower than those in group L(P<0.05);there was no significant difference in the degree of fatness among the groups(P>0.05);the survival rate of group H was significantly lower than that of the other two groups(P<0.05),only(66.67±10.41)%.Total cholesterol and triglyceride decreased with the increase of MLSS,and Urea nitrogen and alanine aminotransferase increased with the increase of MLSS.And there was a significant difference between group L and group H(P<0.05);creatinine was significantly higher in group L than in other two groups(P<0.05),(125.97±9.60)?mol/L;aspartate aminotransferase,globulin,and total protein were the highest in group M.Digestive enzymes:the activity of pepsin and amylase showed the same trend,both decreased with the increase of mixed suspended solids concentration,and the activity of trypsin in group H was significantly lower than that in other two groups(P<0.05);the activity of trypsin in group M reached the highest value,which was(3136.33±175.02)U/m L,while that in group L was only half of that in group M,and the difference between groups was significant(P<0.05);lipase activity was highest in group H and lowest in group M,with significant difference between the two groups(P<0.05).For non-specific immunity,the activity of superoxide dismutase,alkaline phosphatase and catalase increased with the increase of mixed suspended solids concentration;alkaline phosphatase activity was significantly lower in group L only(P<0.05);catalase activity was significantly higher in group H only(P<0.05);the difference of lysozyme activity was no significant(P>0.05).3. Effect of culture density in BFT system on the culture of large-scale Maccullochella peelii peeliiThe effects of different culture densities in the biofloc system(group LD:11 kg/m~3,group MD:22 kg/m~3,group HD:33 kg/m~3)on the water quality,the growth performance,serum biochemical indices,digestive enzymes and non-specific immunity of Maccullochella peelii peelii were studied in a 60-days of experiment period.In terms of water quality,the total ammonia nitrogen concentration was at a low level before 20 days,and after the beginning of differentiation,the group LD<group MD<group HD;the nitrite concentration maintained relatively stable,group HD>group MD>group LD.The concentration of nitrate and phosphate in the three groups increased gradually with the culture time(P<0.05).The average daily weight gain,weight gain rate,visceral volume ratio,hepatopancreas ratio and specific growth rate increased with the increase of culture density,while the feed conversion ratio decreased with the increase of culture density,and the fatness and survival rate reached the highest in the group MD,which were(2.05±0.25)%and(87.78±1.92)%,respectively,but there was no significant difference between the groups(P>0.05).In terms of serum biochemical indices,blood glucose decreased significantly with the increase of culture density;there were no significant differences in cortisol,total cholesterol,triglyceride,glutamate pyruvic transaminase,glutamic oxaloacetic transaminase,albumin and globulin(P>0.05);total protein was the highest in group HD and the lowest in group LD,with significant differences between the two groups(P<0.05).As for digestive enzymes,pepsin activity increased with the increase of culture density,which was significantly higher in group HD than in other two groups(P<0.05);AMS activity in group MD was significantly lower than that in other two groups(P<0.05),trypsin activity in group HD was significantly higher than that in other two groups(P<0.05);lipase activity was not significantly different between groups(P>0.05).The activity of superoxide dismutase were significantly different among the groups(P<0.05),the highest in the group MD and the lowest in the group LD;the activity of catalase and lysozyme were significantly higher in the group MD than in the other two groups(P<0.05);the activity of alkaline phosphatase were lower,and there was no significant difference among the groups(P>0.05).In conclusion,the optimum culture density for breeding Maccullochella peelii peelii in the biofloc system is about 22 kg/m~3.