Effects of diet switching on growth and immunity in Nile tilapia fed a basal, control diet or a diet supplemented with β-glucan

Juvenile Nile tilapia were fed either a basal, control diet or a diet supplemented with 1 g/kg β -glucan for 4 weeks. At the end of this period, half the fish were continued on the same diet or switched to the other diet for 2 weeks. Tilapia were then challenged with Streptococcus iniae by intraperitoneal injection. Groups were split again post-challenge and continued on the same diet or received the alternative diet for another 3 weeks. Feeding regimens were: C-C-C, B-B-B, B-C-B, B-B-C, and B-C-C (C = control, B = β –glucan; 4 weeks-2 weeks-Post-disease challenge). Survival to S. iniae infection was significantly higher in fish fed the β -glucan diet followed by a 2 week basal diet recovery period and then changed back to the β -glucan supplemented diet post-challenge (B-C-B) than fish fed C-C-C or B-B-B. Growth performance was significantly improved in tilapia on β -glucan diets compared to the control after 4 weeks. After 6 weeks, tilapia continuously fed the β -glucan supplemented diets (B-B) had better growth than those fed the control diet uninterrupted (C-C) or switched from the β -glucan diet to the control (B-C) after 4 weeks.