Effect of astaxanthin on the pigmentation of goldfish Carassius auratus

The optimal dosage of astaxanthin for goldfish Carassius auratus was determined by feeding a series of diets containing 0, 25, 50, 75, and 100 mg of astaxanthin/kg of diet for 4 wk. The pigmentation on fish skin was measured by visual assessment against a color chart and by counting chromatophores produced in the dermis layer of fish skin. Both criteria showed that 36–37 mg/kg astaxanthin was the optimal dosage to stimulate fish color. A 4‐wk observation after this experiment demonstrated that fish color stimulated by dietary astaxanthin was stable in its intensity. Therefore feeding astaxanthin could be a suitable way for goldfish producers to stimulate color among fish grown in an algae‐free environment. The survival rate of fish fed diets with astaxanthin was significantly higher than fish fed diets without astaxanthin. However, there was no significant effect of astaxanthin on fish weight gain.