Spirulina platensis in rainbow trout (Oncorhynchus mykiss) feed: effects on growth, fillet composition, and tissue antioxidant mechanisms

An experiment was conducted to investigate the effects of Spirulina platensis (SP) on growth, fillet composition, and intestinal, skin, and gill mucosal antioxidants of rainbow trout, Oncorhynchus mykiss (initial weight 17.18 ± 0.59 g). One-hundred and thirty-five fish were randomly distributed among nine cement tanks (1.8 m × 022 m × 0.35 m) with 15 fish per tank. Three isonitrogenous (37.8% crude protein) feeds containing either 0, 2.5, or 5% SP were prepared, randomly assigned to triplicate tanks of fish, and given at 2% body weight per day for 7 weeks. At the end of the trial, fish in each tank were assessed for growth (final weight, thermal growth coefficient), condition factor, fillet composition, mucosal antioxidant activity, and gene expression analysis related to the antioxidant enzymes catalase, glutathione peroxidase 1, and glutathione S-transferase. Neither growth nor fillet composition was influenced by inclusion of SP in feed. Total antioxidant activity in three mucosal tissues including the intestine, skin, and gill was significantly increased by 2.5% SP whereas administration of 5% SP only increased total antioxidant activity in the intestine. Feeding fish with 2.5% and 5% SP could upregulate the expression of catalase in the intestinal tissue whereas 5% SP enhanced the expression of glutathione peroxidase 1 in this tissue. Glutathione S-transferase gene expression was also increased in the intestinal and skin tissues of fish administrated with 2.5% SP while in the fish that received 5% SP-supplemented diet, an upregulation of this gene was only noted in the intestinal tissue. It was concluded that 2.5% SP had a potential to enhance some antioxidant parameters mostly in the intestine, followed by the skin and gill.