Effect of ascidian (Halocynthia roretzi, Drasche 1884) tunics carotenoids on enhancing growth and muscle coloring of sea-reared rainbow trout (Oncorhynchus mykiss, Walbaum 1792)

• Ascidian tunic as alternative carotenoids supplement for fish culture.
• Rainbow trout’s growth enhancement with dietary ascidian tunics carotenoids.
• Sea-reared rainbow trout’s growth and muscle coloring promoted by ascidian tunic caroitenoids.

A 120 days trial was conducted to investigate the effect of sea squirt (Halocynthia roretzi, Drasche 1884) tunic’s carotenoid to sea-reared rainbow trout (Oncorhynchus mykiss, Walbaum 1792) growth and muscle color. Sea-rearing was done at Tongyeong sea area, Korea. Three dietary treatments, namely control (C), CT, and AT, were administered to 6 groups of fish (n = 490-520). C was given basal diet which has contained 40 mg kg−1 of astaxanthin. A further inclusion of 10 mg kg−1 canthaxanthin was added to diet of CT, while AT’s feed was supplemented with 10 mg kg−1H. roretzi tunics carotenoids extract. The result revealed that AT has the highest final weight (1119.2 ± 82.4 g) compare to those of C (881.0 ± 121.2 g) and CT (1068.2 ± 4.3 g). The specific growth rate (SGR) of AT (1.0 ± 0.07%/day) was significantly higher than C (0.7 ± 0.22%/day) and CT (0.7 ± 0.25%/day) while the feed conversion ratio (FCR) were 1.5 ± 0.6, 1.4 ± 0.6, and 1.2 ± 0.1 for C, CT and AT respectively. The hepatosomatic index (HSI) and Viscerosomatic index (VSI) of all groups showed no significant difference (p > 0.05). The muscle color was also positively affected by the treatments, CT and AT were significantly different from C (p < 005). The initial muscle color score was 1.7 ± 0.0 and the final scores were 3.4 ± 0.2, 5.6 ± 0.1, and 5.7 ± 0.0 for C, CT, and AT respectively. Moreover, muscle carotenoids content of AT (8.5 ± 0.2 mg kg−1) was significantly higher (p < 0.05) than those of CT (6.9 ± 0.3 mg kg−1) and C (6.1 ± 0.2 mg kg−1). Astaxanthin evidently is the most prominent carotenoid present in the muscle from all groups.