Effects of dietary seaweeds (Gracilaria spp. and Sargassum spp.) on growth, feed utilization, and resistance to acute hypoxia stress in juvenile Asian seabass (Lates calcarifer)

The aim of this work was to evaluate the impact of adding Gracilaria spp. and Sargassum spp. to diets on growth performance and resistance to hypoxia stress in Asian seabass. The fish (36.06 ± 0.05 g) were stocked in 18 tanks (200 L), divided into six experimental groups and fed diets containing 0 (control), 3 % (SW3), 6 % (SW6), 9 % (SW9), 12 % (SW12) and 15 % (SW15) Gracilaria and Sargassum mixture in equal proportions for 56 days. Each group consisted of three tanks. Fish were exposed to air for 1 min (hypoxia) and the recovery rate of fish was monitored for 24 h. Results showed that final weight, weight gain, and specific growth rate (SGR) of fish fed the dietary seaweed mixture up to 12 % were significantly higher than fish fed 15 % seaweed powder. Fish fed the 9 % and 12 % seaweed mixture also showed a significantly lower feed conversion ratio (FCR) than the SW15 group. Serum cortisol was significantly higher in the control and lowest in the 12 % seaweed group 6 h post-stress. Hypoxia stress led to significant increases in cortisol values in all fish, but the dietary Gracilaria and Sargassum mixture significantly reduced cortisol values in the SW9 and SW12 groups at 24 h post-stress. Before and 1 h and 24 h after hypoxia, fish fed the 9 % and 12 % seaweed mixture showed significantly lower glucose than the SW15 and control groups. Moreover, serum lactate in the 6–12 % seaweed groups was significantly lower than the control fish at 24 h post-stress. Overall, dietary seaweed showed anti-stress properties and the dietary Gracilaria and Sargassum mixture at levels of 9–12 % increased resistance to hypoxia stress in fish. The present results showed that seaweed (Gracilaria and Sargassum mixture) up to 12 % level is useful in the diet of juvenile Asian seabass.