Behavior,Growth And Physiological Response Of Tilapia (Oreochromis Niloticus,Gift Strain) In Different Light Qualities

Light,including light quality,light intensity and photoperiod,plays a role in regulating behavior,feeding,growth and endocrine system of fish.Suitable light condition benefits the growth of fish,while unsuitable light condition causes stress in fish.In aquaculture,using light to regulate the feeding behavior and growth performance of fish,as well as to alleviate the stress of fish in intensive aquaculture,has been frequently reported.Tilapia is one of the main economic freshwater fishes in China,but there were few studies on the growth and physiological response of tilapia to different light qualities and on the relationship between them.To improve the health and welfare of cultured tilapia,the suitable light condition for tilapia will be explored and the underlying physiological mechanisms will be revealed.In the present study,tilapia(Oreochromis niloticus,GIFT strain)were exposed to different LED light quality(red,yellow,blue,green and white)to study the light preference,growth and physiological responses of tilapia.The main findings are as follows:(1)Research on the preference of young GIFT tilapia for different light qualitiesThere were significant differences in preference of tilapia for the 5 light qualities,but there was no difference in preference for the same light quality between day and night.During the day,23.89% of tilapia stayed in the central area and 20.00% entered the yellow light compartment.The distribution rate of tilapia in the yellow light compartment was significantly higher than that in the blue,green,red and white light compartment(P<0.05),but had no significant difference from that in the dark area.The preference of tilapia for light quality had no significant difference between day and night(P>0.05).The findings suggested the yellow light was an ideal light quality for tilapia,which was suitable for tilapia welfare.(2)Growth and physiological response of juvenile GIFT tilapia in different light qualitiesThe study on the growth of tilapia juveniles under 5 light qualities showed that tilapia juveniles grew faster in the red and white light than the others.The body weight(BW)of the tilapia juveniles exposed to red or white light were significantly higher than that in yellow,blue,green light and control group(P<0.05);the body length(BL)of tilapia juveniles in the white light group was significantly higher than that in the other 5 groups(P<0.05),and the specific growth rate(SGR)was significantly higher than that in the blue light group,but was not significantly different from the other 4 groups(P>0.05);the condition factor(CF)of tilapia juveniles in the yellow light group was significantly higher than that in the blue light,green light and control group(P<0.05),but was not significantly different from the white and red light groups(P>0.05).The crude protein content of tilapia juveniles in the white,red and blue light groups were significantly higher than that in the control group(P<0.05),and was the lowest in the yellow light group.The digestive enzymes and antioxidant defense system of tilapia juveniles were affected by light qualities.The activity of alkaline phosphatase(AKP)in the digestive tract of tilapia juveniles exposed to red and yellow light were significantly higher than that in the other 4 light quality groups(P<0.05),and was the lowest in the white light group;The activities of pepsin(PES)in the digestive tract of tilapia juveniles in the white light group was significantly higher than that in the other 5 groups(P<0.05);The activity of α-amylase(α-AMS)in the digestive tract of tilapia juveniles in the red light group was significantly higher than that in the other 5 groups(P<0.05);The activity of lipase(LPS)in the digestive tract of tilapia juveniles in the yellow light group was the highest,but was not significantly different from the red and white light groups(P>0.05).The total antioxidant capacity(T-AOC)in the liver of tilapia juveniles in the yellow light group were the highest,followed by the white,the red,blue,green and control group.The activity of superoxide dismutase(SOD)in the liver of fish juveniles in the control group was not significantly different from that in the green light group,but was significantly higher than that in the other 4 groups(P<0.05);The catalase(CAT)activity in the liver of fish juveniles in the control group was not significantly different from the red and yellow light groups,but was significantly lower than that in the white,blue,and green light groups(P<0.05).In short,red and white light significantly improved the growth rate of tilapia juveniles;Red,white and yellow light enhanced the antioxidant capacity in the liver of tilapia juveniles and improved the digestion and absorption capacity of tilapia juveniles.Although white light promoted the growth of juvenile tilapia,it had a negative impact on the physiological response of juvenile tilapia,just like green light and blue light.Thus white,green and blue light were detrimental to the welfare of juvenile tilapia.(3)Growth and physiological response of young GIFT tilapia in different light qualitiesAfter 6-week experiment,the results showed that different light quality affected the feeding and growth status of young tilapia.The feeding rate(FR)and weight gain rate(WGR)of the tilapia exposed to yellow or red light were higher,and feed conversion ratio(FCR)were significantly lower(P<0.05)than those in the other light quality groups;The feeding rate,weight gain rate and specific growth rate(SGR)in the green light group and dark group were the lowest.Although light qualities had no significant effect on ash and crude protein content of tilapia,they affected the crude lipid and moisture content of tilapia.The crude lipid content of tilapia in the yellow light group was not significantly different from the blue light group(P>0.05),but was significantly higher than the other4 groups(P<0.05);the moisture content of tilapia in the yellow light group was not significantly different from the red and blue light groups(P>0.05),but significantly lower than the green,white and dark groups(P<0.05).Activities of protease(PES)and α-amylase(α-AMS)in the stomach of tilapia of the red light group were significantly higher than those in the other light groups(P<0.05);The activity of lipase in the red light group was significantly lower compared with the white light group and the dark group(P<0.05),but there was no significant difference among other groups.The cortisol concentration in the plasma of tilapia exposed to green light was significantly higher than that in the other groups(P<0.05),which indicated that the green light had a stress effect on tilapia.The lysozyme(LZM)activity in the serum of tilapia exposed to yellow light was significantly higher than that in the other groups(P<0.05).The findings above indicated that red light enhanced the digestive ability of young tilapia and yellow light improved the nonspecific immunity of tilapia,both yellow and red light decreased the feed conversion ratio and promoted the growth of tilapia.Green light induced a stress response in tilapia and had a negative effect on the growth of tilapia.In conclusion,the young GIFT tilapia preferred yellow light;Moreover,yellow light improved the growth performance and resistance of tilapia in different life stages,which is beneficial to the welfare of tilapia.For tilapia juveniles,red light can also be used as the farming light environment.This research provided a basic theory for choosing light quality conditions for the welfare of tilapia.