Effects Of Photoperiod On The Skin Color,Growth Performance,hepatic Anti-oxidative Enzyme,and Blood Biochemical Composition Of Red Tilapia

Red tilapia farming is challenged by skin color differences and growth retardation especially in areas where seasonal environmental changes do not favor tilapia farming.Manipulation of photoperiod in aquaculture is vivid,it is considered as one of the important environmental factors to enhance growth,control reproduction and affect skin pigmentation in fish.For the healthy aquaculture production,fish welfare in any manipulated environment is highly considered.In this study,investigation of the skin color,growth performance,gonadal maturation,anti-oxidative enzymes,and serum blood composition on Malaysian red tilapia cultured under different photoperiods i.e.prolonged light(24L:0D,Light:Dark),prolonged darkness(about 0L:24D)and natural photoperiod(13L:11D)were done.Effect of photoperiod on the growth performance and gonadal maturation of Malaysian red tilapiaAfter 78 days of experiment,final weight(FW),weight gain rate(WGR)and specific growth rate(SGR)of fish under prolonged darkness(0L:24D)and prolonged light(24L:0D)were both significantly higher(P<0.05)compared to fish under natural photoperiod(13L:11D).No significant effects were observed for both female and male gonadal somatic index(GSI)among all photoperiod regimes.Effect of photoperiods on the skin color of red tilapiaFish color phenotype,gene expression and melanin contents(tyrosine and cysteine)varied according to different photoperiods.Fish reared under prolonged light exposure displayed pale pink color while in dark conditions fish displayed a pink-reddish color and in natural photoperiod fish were all pink.In ventral skin,tyrosinase was significantly higher(P<0.05)under prolonged darkness while cysteine level showed no significant difference among the photoperiod regimes.In dorsal skin no significant differences in tyrosinase level were observed,but the cysteine level was significantly higher under natural photoperiod than other photoperiods.Relative gene mRNA expressions were also affected by photoperiod.In ventral skin Sox 10,tyr,slc7a11 and tyrp-1 were highly expressed under prolonged darkness than other photoperiods,while the lower expression was in prolonged light.No significant effect in gene expression on the dorsal skin under different photoperiodsEffect of photoperiod on the hepatic anti-oxidative enzymes and serum blood biochemical compositionSignificant differences of Ant-oxidative enzyme were obtained among the photoperiod regimes.All anti-oxidative enzymes,SOD,CAT,GHS-Px and MDA were significantly higher(P<0.05)in prolonged light(24L:0D)than in both prolonged darkness(0L:24D)and natural photoperiod(13L:11D).SOD activities observed high under prolonged light than both prolonged darkness and natural photoperiod.CAT was high in prolonged light followed by natural photoperiod and lowest concentration observed in prolonged darkness.GHS-Px was significant high in both prolonged light(24L:0D)and darkness(24D:0D)than natural photoperiod.MDA concentration was high in light followed by dark and lowest in natural photoperiod.Sixteen blood biochemical components were analyzed in this study,among them,the only ALT,AST,ALP,LDH,CK-MB,CREA,and C1 showed a significant difference.ALT,AST,ALP,and LDH were observed significant higher(P<0.05)in prolonged light(24L:0D)than both prolonged darkness(0L:24D)and natural photoperiod(13L:11D).CK-MB was observed significant higher(P<0.05)in prolonged darkness than other photoperiod regimes while CREA observed to be significantly higher(P<0.05)in natural photoperiod than other photoperiod regimes.No significant difference(P>0.05)recorded for ALB,GLO,and A/G.Also,there was no significant effect of photoperiod on the nutritional indicators in blood serum(TP,CHOL,and TG).Ion parameters/electrolytes were differentially expressed,Cl was significant higher(P<0.05)in prolonged light than other photoperiods,and no significant difference(P>0.05)were observed for Na,K and Ca.Generally,Application of prolonged darkness observed to have a positive effect in many parameters including growth,fish body color and good physiological status of fish.Prolonged light had a positive effect on growth however the color of fish was negatively affected by light.Also in prolonged light,the level of anti-oxidative enzymes and serum blood indicators were high compared to the other two photoperiods.Hereby this study suggests that understanding of the effects of photoperiod on red tilapia will help in selective breeding program of the important economic traits for the development of commercial red tilapia farming.