The Application Of Astaxanthin,Xanthophyll And Sodium Taurocholate In The Feed Of Discus Fish (Symphysodon Aequifasciata)

Exp.1 Dietary astaxanthin improved the body pigmentation and antioxidant function,but not the growth of discus fish(Symphysodon aequifasciata)To assess the effects of synthetic astaxanthin on growth and body color of red discus fish(Symphysodon aequifasciata),synthetic astaxanthin was added into the basal diet(beef heart hamburg)with the levels of 0(control diet),50,100,200,300 and 400 mg/kg(effective concentration)respectively.The six experimental diets were fed to discus fish with an initial body weight of 10.3 ± 0.8 g for 8 weeks.The results showed that the supplementation of astaxanthin at 50-200 mg/kg had no significant effects on growth performance of discus fish,but the high supplementation of astaxanthin(300 or 400 mg/kg)significantly reduced the weight gain and increased the feed coefficient ratio(P < 0.05).After 4 or 8 weeks of feeding,the L*(lightness)values in astaxanthin-supplemented groups were significantly lower,while a*(redness),b*(yellowness)and skinastaxanthin contents were higher than the control group(P<0.05).When the astaxanthin supplementation reached 200 mg/kg,skin redness and astaxanthin contents remained relatively stable.When b* was relatively stable,the supplemental astaxanthin was 300(4 weeks)and 50 mg/kg(8weeks)respectively.With the supplemental astaxanthin increasing,the astaxanthin retention rate significantly decreased and hepatic total antioxidant capacity was strengthened.The dietary astaxanthin also significantly reduced the glutathione level(P<0.05)when the astaxanthin inclusion was higher than 50 mg/kg.The above results showed that dietary astaxanthin could effectively improve the skin pigmentation of red discus fish in 4 weeks and the supplementation level was suggested to be 200mg/kg.Exp.2 Effect of dietary xanthophyll on the growth and body color of discus fish(Symphysodon aequifasciata)To assess the effects of dietary xanthophyll on the growth and body color of discus fish(Symphysodon aequifasciata),xanthophyll was added into the basal diet(beef heart hamburg)with the levels of 0,50,100,200,300 and 400 mg/kg respectively.The six experimental diets were fed to discus fish with an initial body weight of 10.3 ± 0.8 g for 8 weeks.The results showed that the supplementation of 50-200 mg/kg xanthophyll had nosignificant effects on the weight gain rate,but the feed coefficient ratio significantly increased and the weight gain rate significantly decreased when the xanthophyll supplementation reached 200 or 300 mg/kg respectively.After 4 or 8 weeks’ feeding,the skin lightness(L*)showed no significant differences among groups,but the skin yellowness(b*)increased with the increase of dietary xanthophyll.The b* value and xanthophyll content in skin of all xanthophyll-supplemented groups at the8 th week were higher than those at the 4th week.The b* values at the 4th week and 8th week,and the xanthophyll content in whole fish at the 8th week remained relatively stable when the xanthophyll supplementation reached 300 mg/kg.At the 4th week,the skin redness(a*)showed no significant difference among groups,but at the 8th week,the a* values significantly decreased when the xanthophyll supplementation reached 100mg/kg.The hepatic total antioxidant capacity was significantly strengthened by the supplementation of 300 or 400 mg/kg xanthophyll.The above results showed that dietary xanthophyll could effectively improve the yellowness of the skin and strengthen the hepatic total antioxidant capacity of discus fish,but the high inclusion of xanthophyll decreased the growth of the fish.The supplementation level of xanthophyll was suggested to be 100 mg/kg from the aspect of growth;the supplementation level of xanthophyll was suggested to be 200-300 mg/kg to enhance the skinyellowness of discus fish.Exp.3 Effect of dietary sodium taurocholate on the growth and body color of discus fish(Symphysodon aequifasciata)To assess the effects of dietary sodium taurocholate on the growth and body color of discus fish,two inclusions of astaxanthin at 100 and 200 mg/kg were added into the basal diet(beef heart hamburg),referred as negative control(A100)and positive control(A200)respectively.Then sodium taurocholate was added into A100 diet with inclusion levels of 400,800,1200,1600 and 2000 mg/kg respectively.The seven diets were fed to discus fish with an initial body weight of(31.6 ± 2.0)g for 6 weeks.The results showed that the supplementation of 400-2000 mg/kg sodium taurocholate significantly increased the condition factor of discus fish(P<0.05),and the supplementation of 2000 mg/kg sodium taurocholate significantly improved the weight gain rate(P < 0.05),when compared with the A100 group.With the increase of sodium taurocholate inclusion,the values of anterior skin redness(a*)and yellowness(b*)increased,tended to be stable when the supplemental level reached 1200 mg/kg and were significantly higher than A200 group,the values of posterior skin redness(a*)reached the maximum value at the supplemental level of 800mg/kg and was significantly higher than A200 group.The skin astaxanthincontents increased firstly,and then decreased.The skin astaxanthin content showed the maximum value,sinificantly higher than A100 group but lower than A200 group(P < 0.05)when the supplemental inclusion was 1200mg/kg.The astaxanthin relative retention coefficient in skin of discus fish fed the feed supplemented with 400,800 and 1200 mg/kg sodium taurocholate was significantly higher than that of fish fed A100 and A200 diet,the astaxanthin content and relative retention coefficient both showed the highest values when the supplemental inclusion levels was 800 and1200 mg/kg.The above results showed that the supplementation of sodium taurocholate in low astaxanthin feed could improve the utilization of astaxanthin,the body color of discus fish and the body shape.The supplemental level was suggested to be 800-1200 mg/kg.