Effects of low molecular weight sodium alginate on growth performance, immunity, and disease resistance of tilapia, Oreochromis niloticus

• Oreochromis niloticus fed with 10 g kg−1 LMWSA enhanced growth performance.
• Fish fed 10 g kg−1 LMWSA significantly stimulated innate immune response of O. niloticus.
• Fish fed 10, 20 and 30 g kg−1 LMWSA significantly increased post challenge survival rate of O. niloticus against Streptococcus agalactiae.

Present study was carried out to evaluate the effects of low molecular weight sodium alginate (LMWSA) as potential prebiotic source on growth performance, innate immunity and disease resistance of tilapia, Oreochromis niloticus. Three hundred twenty fish were divided into four treatments and fed following diets 0 (T1- Control), 10 (T2), 20 (T3) and 30 (T4) g kg−1 LMWSA for period of 60 days. A Completely Randomized Design with four replications was applied. At the end of experiment, fish in each replication were weighed and specific growth rate (SGR) and feed conversion ratio (FCR) were calculated. Five randomly selected fish were used for innate immune response measurement. Another ten fish were randomly selected for challenge test against Streptococcus agalactiae for a period of 18 days. The lysozyme, complement, phagocytosis, and respiratory burst activities were detected after 60 days of feeding trial and after challenge test. The results indicated that fish fed diet 10 g kg−1 LMWSA significantly improved SGR and FCR after 60 days of feeding trial. The lysozyme, phagocytosis, respiratory burst, and complement activities were significantly higher in fish fed LMWSA diets compared to control. Fish fed 10 g kg−1 LMWSA had greatest values compared to fish fed 20 and 30 g kg−1 LMWSA. The survival rate of O. niloticus was significantly improved in fish fed LMWSA diets after challenge with S. agalactiae for 18 days. However, no significant difference in survival rate was observed among LMWSA supplemented diets. It is indicated that fish fed 10, 20 and 30 g kg−1 LMWSA diets can stimulate growth performance, innate immunity and disease resistance in tilapia against S. agalactiae.