Effects of dietary Gracilaria persica on the intestinal microflora, thyroid hormones, and resistance against Aeromonas hydrophila in Persian sturgeon (Acipenser persicus)

Red seaweeds have several biomedical derivatives making them healthy additives for the aquaculture industry. Previously we reported enhanced growth performance, feed utilization, and immunity of Persian sturgeon treated with Gracilaria gracilis. Herein, we investigated the effects of G. gracilis on the intestinal microflora, thyroid hormones, and resistance against Aeromonas hydrophila in Persian sturgeon. Fish fed G. gracilis at 0, 2.5, 5, and 10 g/kg for eight weeks, then challenged with A. hydrophila for ten days. The results showed that the total bacterial count in the fish intestines had no meaningful differences among the groups of fish fed varying levels of G. persica (P˃0.05). Fish fed 10 g/kg of G. persica had a higher lactic acid bacteria (LAB) count than fish fed 0, 2.5, and 5 g/kg (P<0.05). Serum thyroid-stimulating hormone (TSH) showed higher levels in fish treated with 2.5 and 5 g/kg of G. persica than the other groups (P<0.05). Besides, fish fed 2.5 g/kg G. persica had higher thyroxine (T4) and triiodothyronine (T3) levels than the other groups (P<0.05). At the end of the challenge test, the highest mortality was seen in the fish fed the G. persica free diet. In summary, Persian sturgeon treated G. gracilis had improved intestinal microflora, thyroid hormones, and resistance against A. hydrophila.