Aquaculture Reports (Apr 2024)
Investigating the effect of hydroalcoholic extract of red algae (Laurencia caspica) on growth performance, mucosal immunity, digestive enzyme activity and resistance to Streptococcus iniae and Aeromonas hydrophila in Nile tilapia (Oreochromis niloticus)
Abstract
Immunostimulants, including seaweed, can play a significant role in increasing the immune response and preventing the occurrence of diseases in aquatic animals. These stimulants increase the fish’s disease resistance by strengthening the nonspecific immune system. This study aimed to investigate the effects of red macroalgae extract Laurencia caspica (Lc) on mucosal immunity, growth, serum biochemical parameters, serum and mucus bactericidal activity, digestive enzymes, and disease resistance against S. iniae and A. hydrophila in Nile tilapia. Fish with an average weight of 100 ± 2 g were fed with Lc algae extract at four levels (0, 0.5, 1 and 2%) for 50 days. The weight gain (WG), food conversion ratio (FCR), and specific growth rate (SGR) significantly increased compared to the control group (P 0.05). However, it was a significant increase in the mucus (P 0.05), although triglyceride (TG) in Lc 2% on the 25th day had a significant increase compared to the control group (P < 0.05). Lysozyme (except Lc 0.5% on the 50th day) and total immunoglobulin (Ig) (in all groups) of the mucus had a significant increase compared to the control group (P < 0.05). The activity of digestive enzymes such as trypsin and α-amylase on the 25th and 50th days in Lc 1 and 2% increased significantly compared to the control group (P < 0.05). Lipase enzyme activity in all algae extracts groups increased substantially on the 25th and 50th days compared to the control group (P < 0.05). The survival rate of fish challenged with S. iniae and A. hydrophila was significantly higher than the control group (P < 0.0001). Overall, it can be concluded that Lc algae extract can increase mucosal immunity. Also, the Lc extract induces fish resistance to S. iniae and A. hydrophila and can improve Nile tilapia growth.
