Effect Of Salinity On The Growth Performance,Physiological Responses And Muscle Quality Of Juvenile Freshwater Drum(Aplodinotus Grunniens)

The freshwater drum Aplodinotus grunniens is a species commonly distributed in North and South American and supports artisanal fishery.It is the only species in its family that has permanently adopted the freshwater habitat.Its first artificial propagation was successful in the year 2019 in China.In order to expand the area of culture of this species,the present study was conducted to supply detailed information on other suitable cultured environment for freshwater drum.In this regard,an acute and chronic salinity stress test was designed to examine the differences in survival rate,growth performance,physiological responses,muscle quality and osmotic pressure of juvenile freshwater drum in different salinities from 0‰ to 15‰.Results from the various experiments are as follows;The acute salinity experiment showed that the juvenile freshwater drum in different salinity levels(0‰,5‰,7.5‰,10‰,12.5‰,15‰,17.5‰,20‰,25‰)can only survive up to 15‰.Based on the acute results above,a chronic salinity experiment was set up under salinity levels(0‰,4‰ 8‰ 12‰)for 36 days to determine the growth performance of the juvenile freshwater drum.Growth performance included the weight gain rate,specific growth weight,Survival rate,Visceral somatic index and Hepatic somatic index.The results showed significant differences in growth performance under the various salinity stress conditions with the best achieved at 8‰ salinity(P < 0.05).A different set of acute salinity stress test was designed to examine the digestive enzymes,antioxidant capacities biochemical responses and gene expression of the juveniles in different salinities(0‰,7.5‰,15‰)at different sampling times(0h,4h,12 h,24h,48 h,and 96h).The digestive enzymes involved lipase,α-amylase,and pepsin in the intestines.The results from lipase and α-amylase showed no difference(P >0.05),while pepsin activities displayed significant difference compared to the control in the different salinity levels(P <0.05).Antioxidant enzymes included Superoxide dismutase,Catalase,Malondialdehyde,Total antioxidant in the liver as well as Sodium potassium adenosine triphosphate activities in the gills.The results displayed significant differences in the antioxidant activities as well as the sodium potassium adenosine triphosphate enzymes in the different salinity levels compared to the control(P <0.05).Biochemical activities involving Alanine aminotransferase and Aspartate transaminase where examined in the liver.The results at7.5‰ showed no significant difference compared to the control(P > 0.05).In the study,Heat shock proteins 70 and Heat shock proteins 90 genes in the gills and liver were examined.The results displayed no significant difference in the 7.5‰ compared to the control(P > 0.05).Finally,muscle quality and osmotic pressure were examined and its results displayed no significant difference across the different salinity levels compared to the control(P > 0.05)Conclusions gathered from the study revealed that the juvenile freshwater drum would not survive in salinity levels above 15‰,however growth performances are optimum at 8‰ while physiological responses from the study revealed that salinity levels at 7.5‰ would not cause damage to fish tissues.Muscle quality and osmotic pressure remained unaffected.