To assess the effects of dietary astaxanthin on the growth and body colour of red discus fish (Symphysodon spp.), synthetic astaxanthin was added into the basal diet (beef heart hamburger) with the levels of 0 (control diet), 50, 100, 200, 300 and 400 mg kg À1 respectively. The six experimental diets were fed to discus fish with an initial body weight of 10.3 AE 0.8 g for 8 weeks. The results showed that the supplementation of 50-200 mg kg À1 astaxanthin had no significant effects on growth performance of discus fish, but the high supplementation of astaxanthin (300 or 400 mg kg À1 ) 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 skin astaxanthin contents were significantly higher than the control group (P < 0.05). When the astaxanthin supplementation reached 200 mg kg À1 , skin redness and astaxanthin contents remained relatively stable. When b* was relatively stable, the supplemental astaxanthin was 300 (4 weeks) and 50 mg kg À1 (8 weeks) respectively. With the supplemental astaxanthin increasing, the astaxanthin retention rate significantly decreased and hepatic total antioxidant capacity was strengthened. The dietary astaxanthin also significantly increased the reduced glutathione level (P < 0.05) when the astaxanthin inclusion was higher than 50 mg kg À1 . 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 200 mg kg À1 .

A study was conducted to evaluate the effects of organic acid salt blend (OAB), protease complex (Pr) and their combination (OAB+Pr) in fish meal‐free diets on growth, nutrient retention and digestibility of tilapia. Five diets were designed: a positive control (PC) diet containing 80 g/kg fish meal (FM), a negative control (NC) diet containing 0 g/kg FM and 104 g/kg meat and bone meal, and three other diets supplemented with OAB (922 mg/kg), Pr (175 mg/kg) and OAB+Pr (922 mg/kg + 175 mg/kg) to the NC diet. Tilapia with an initial body weight of 7.0 ± 0.2 g were fed the five diets for 9 weeks. The results showed that the growth performance, nutrient digestibility and retention of NC group had the lowest values among groups. Weight gain of fish fed the OAB and OAB+Pr diets was higher, and feed conversion ratio was lower (p < 0.05) compared to those fed the NC diet, while no differences with those fed the PC diet. The digestibility of dry matter, crude protein, minerals and protein retention was improved in fish fed the OAB+Pr diet (p < 0.05), but not in those fed OAB or Pr diet (p > 0.05). There were no differences in whole‐body composition and lipid retention among the treatments (p > 0.05). The supplementation of OAB and Pr alone or combined significantly increased the villi height but not the width when compared to the NC group. It can be concluded that dietary supplementation of OAB+Pr in a fish meal‐free diet improves growth and nutrient digestibility in tilapia compared to those fed the fish meal‐free diet.

To investigate the effects of dietary quercetin on growth, antioxidation, and flesh quality of grass carp, Ctenopharyngodon idella, six diets were prepared with quercetin inclusion rates of 0 (control diet), 0.1, 0.2, 0.4, 0.6, and 0.8 g/kg. Grass carp with a body weight of 13.3 ± 0.1 g were fed with one of the six diets for 60 days. The weight gain (WG) showed a quadratic relationship with dietary quercetin levels; the supplementation of 0.4 g/kg quercetin significantly improved WG (+4.73%) and decreased feed conversion ratio (−0.06) (p < .05) when compared to those of the control group. The intestinal fat ratio was reduced by the addition of 0.2 or 0.4 g/kg of quercetin (p < .05), and serum activities of alkaline phosphatase and superoxide dismutase were increased by the addition of 0.4 and 0.6 g/kg of quercetin (p < .05). The inclusion of 0.2–0.6 g/kg of quercetin increased the contents of delicious amino acids and decreased the cooking loss of flesh (p < .05). Flesh collagen content was increased by the addition of 0.4–0.8 g/kg of quercetin (p < .05). In conclusion, dietary quercetin could improve the growth and enhance the antioxidation and flesh quality of grass carp, with the recommended supplemental level of quercetin was 0.37 g/kg.

No abstract

Eight isolipidic diets containing 0, 20, 40, and 60 g/kg oxidized fish oil (OFO) or oxidized soybean oil (OSO) were fed to triplicate groups of channel catfish, Ictalurus punctatus, for 8 weeks to investigate the effects of oxidized oils on growth, body color, and antioxidative capacity. Lower weight gain (WG) was observed in fish fed high levels of oxidized oils (40 and 60 g/kg) (p < .05). At the inclusion of 40 g/kg, OFO group showed lower WG than the OSO group (p < .05). With the increase of dietary oxidized oils, the serum levels of malondialdehyde, total bilirubin, direct bilirubin, and activity of alanine aminotransferase and aspartate aminotransferase significantly increased (p < .05), but the glutathione level decreased (p < .05). Serum superoxide dismutase and catalase activity showed the maximum values at 20 g/kg OFO group and 40 g/kg OSO group, respectively. Compared to the 0 g/kg oxidized oil groups, both dietary oxidized oils increased the b* value (yellowness) of dorsal skin and caudal skin at 40 and 60 g/kg inclusion (p < .05). In conclusion, dietary oxidized oil (≥40 g/kg) decreased the growth and the antioxidative capacity and increased the yellowness of skin. OFO caused more negative effects on channel catfish than OSO at the inclusion of 40 g/kg.