Dietary astaxanthin improved the body pigmentation and antioxidant function, but not the growth of discus fish (Symphysodon spp.)

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−1 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−1 astaxanthin had no significant effects on growth performance of discus fish, but the high supplementation of astaxanthin (300 or 400 mg kg−1) significantly reduced the weight gain and increased the feed coefficient ratio (P