Evaluation of a Dietary Dairy–Yeast Prebiotic in Juvenile Golden Shiners in Ponds

We evaluated the performance in ponds of juvenile golden shiners Notemigonus crysoleucas fed a control diet or a diet with 2% dairy–yeast prebiotic. Fish weighing 0.1 ± 0.001 g (mean ± SD) were initially stocked into five 0.04‐ha earthen ponds per diet at 21.9 kg/ha and fed extruded 35%‐protein pellets to satiation twice daily. Subsamples of fish were weighed at 2‐week intervals for 6 weeks; the fish were harvested at 7 weeks to avoid reproduction. For golden shiners fed the control and prebiotic diets, the mean individual weight gain (2.93 and 2.89 g, respectively), net yield (214.0 and 198.8 kg/ha), feed conversion ratio (1.34 and 1.47), and survival (61.5% and 64.2%) did not differ. Condition index (Fulton's K ) was higher in fish fed the control (1.15) rather than the prebiotic diet (1.08). After harvest, 100 fish per pond were acclimated to tanks before being subjected to a bacterial challenge with Flavobacterium columnare . Each pond replicate received one of three experimental treatments: confinement stress for 30 min before F. columnare exposure (stressed), no stress before F. columnare exposure (unstressed), or no stress or exposure to F. columnare (control). Whole‐body cortisol increased in stressed fish regardless of diet. After release, fish were exposed to a virulent strain (PB02) of F. columnare for 18 h. Survival over 14 d ranged from 98.3% to 100% among fish in the control and unstressed treatments fed either the control or prebiotic diets. The stressed golden shiners fed the prebiotic diet had mortality rates similar to those of the unstressed fish fed the control or prebiotic diet, but the stressed fish fed the control diet had lower mean survival (73.3 ± 4.4%) than those fed the prebiotic diet. Preliminary economic analysis indicates that the higher cost of feed containing a 2% prebiotic may be justified based on the increased survival of golden shiners in tanks exposed to stressors and pathogens.