The Effects Of Dissolved Oxygen Levels On Growth Performance,physiological Parameters And The Immune Response Of The Gift Juveniles(Oreochromis Niloticus)with Three Different Levels Of Dietary Protein

Tilapias as one of the widely farmed fish species have gained popularity in most regions of the world.In isolation from the inclusive varieties of tilapia,the genetically improved farmed tilapia(GIFT)has gained a prestigious niche at the commercial level in China and regarded as the optimum reform towards the development of emerging aquaculture industries in most regions of Africa.This is basically articulated by the species special characters that appeal to the preference of the farmers in the aquaculture industry Inevitably,nutritional status and environmental conditions represent the mainstay aspects of the successful farming of these species.Hence,the effects of dissolved oxygen(DO)levels on growth performance,physiological parameters,and immunity in the juvenile GIFT treated with three varying levels of dietary protein were studied in a 6-week experiment.Juvenile GIFT(0.45±0.01g)were cultured under hypoxia(2.0±0.3 mg/l)and normoxia(6.0±0.4mg/l)DO levels,and fed with 30%,40%and 50%protein diets.The triplicate groups of fish were hand-fed to apparent satiation twice a day(8:00 and 16:00 hours).The effects of dissolved oxygen levels on growth performance,feed utilization and somatic indices in the GIFT juveniles with three different levels of dietary proteinThe final body weight(FBW),weight gain(WG),and specific growth rate(SGR)were reduced after hypoxia exposure(P<0.01),and improved after the increasing dietary protein levels.The individual and interaction effects of DO and dietary protein levels on the feed intake were significant(P<0.01).The feed intake tended to increase linearly with the concurrent increasing DO and dietary protein levels.Protein efficiency ratio(PER)increased significantly with an inverse decrease in dietary protein level(P<0.01).PER was not changed by DO.The feed conversion ratio(FCR)reduced inversely with an increasing DO(P<0.01).Hepatosomatic index(HSI)endured the significant effects of both DO and dietary protein levels(P<0.01),while viscerosomatic index(VSI)was affected by DO alone and the combination with dietary protein levels(P<0.01).These results showed that hypoxia adversely affected the growth performance and feed utilization of the GIFT juveniles.The effects of dissolved oxygen levels on hematological and blood serum parameters of the GIFT juveniles with three different levels of dietary proteinThe effects of DO and dietary protein levels on hematological parameters involving the white blood cells(WBC)count,hematocrit(HCT)and hemoglobin(HGB)were not significant(P>0.05),apart from the significantly reduced red blood cells(RBC)count after hypoxia exposure(P<0.01).The blood serum parameters involving aspartate aminotransferase(AST),alanine aminotransferase(ALT),total protein(TC),triglyceride(TG),and total protein(TP)of the fish increased significantly at the hypoxia condition(P<0.05).The independent effects of dietary protein levels on ALT,glucose(GLU),and TP contents were significant(P<0.05).Of the plasma serum parameters,only TG showed a significant response to the combined effects of DO and dietary protein levels,respectively(P<0.05).These findings present that hypoxia significantly impaired the liver of the fish.The effects of dissolved oxygen levels on immune and antioxidant enzymatic activities in the liver,serum,gill,intestine and muscle of the GIFT juveniles with three different levels of dietary proteinIn terms of the antioxidant enzymes activity,the results showed that DO significantly induced alterations on the catalyst(CAT),superoxide dismutase(SOD),malondialdehyde(MDA)in the liver(P<0.05),and the SOD was also affected by the dietary protein(P<0.05).The insignificant results were observed on the glutathione peroxidase(GSH-PX)(P>0.05).The insusceptibility of fish regarding complement component 3(C3(C3))was significantly reduced at the hypoxic condition(P<0.05).The serum lysozyme(LZM)and D lactic acid(D-Lac)were unchanged by either DO or dietary protein levels(P>0.05).The increasing lipase(PL)and decreasing amylase(AMY)were observed after hypoxia exposure,with no interaction effects detected.Trypsin(TRY)showed no significant response to either DO or dietary protein levels(P>0.05).The cytochrome C oxidase(COX)and lactate dehydrogenase(LDH)in the muscle and gill were significantly changed by the dietary protein levels.The combined effects of DO and dietary protein levels were observed in the muscle on COX activity(P<0.05).The effects of dissolved oxygen and dietary protein levels on muscle D-Lac were not significant.The higher LDH activity was observed in the fish fed at the low dietary protein level,wherein the decreased LDH induced by the excess dietary protein level in the muscle(P<0.05).COX activity in the gill was significantly affected by the DO independently.These data showed that hypoxia is detrimental to the fish insusceptibility.