Use of fermented malted barley by-product as partial feed replacement and carbon source for rearing Nile tilapia (Oreochromis niloticus) juveniles

The present research evaluates the performance of the Nile tilapia (Oreochromis niloticus) (initial weight 11.5 ± 0.07 g) with biofloc technology. For this purpose, spent grains (malted barley) from the brewing industry after aerobic fermentation were used, as both a carbon source (suspended solids) and partial substitute for the diets at 0, 10, 20, 30, and 40% levels (settleable solids). The partial 20% substitution of the diet did not have significant effects on the biological parameters: final body weight, weight gained, average body weight, specific growth rate, daily growth index, condition factor, feed conversion ratio, protein efficiency rate, and viscerosomatic and hepatosomatic indices. However, the dietary substitution showed a significant effect on the final biofloc chemical composition. Nitrogen compounds, NH₄⁺, NO₂⁻, and NO₃⁻, were adequate for tilapia cultivation in all the treatments. No clear effect of partial dietary substitution was observed on meat quality parameters: pH, color, water holding capacity, and amino acid and fatty acid profile of fillet. The results suggest that a 20% substitution of the diet for malted barley is suitable for satisfactory biological parameters and Nile tilapia fillet quality.