Evaluation of fermented silage made from fish, tomato and potato by-products as a feed ingredient for Nile tilapia, Oreochromis niloticus

Abstract

ish by-products were fermented with Lactobacillus plantarum at 30°C using molasses as carbohydrate source. The ensilage process was completed after 30 days and at the end, a desirable and stable pH (4.5) was attained. Dried tomato by-product meal (TBM) and potato by-product meal (PBM) were used as alternative filler and blended with the liquid silage (40:30:30 w/w) and sundried. The resulting dried silage meal was included in the experimental diets to replace 0, 10, 20, 30, 40 or 50% of dietary protein (by weight) in isonitrogenou s (30% CP) and isocaloric (2700 kcal ME/kg) pelleted diets. No significant differences were found for apparent digestibility coefficient (ADC) of dry matter (DM), crude protein (CP), ether extract (EE) and nitrogen free extract (NFE) up to 30% inclusion level, while the highest inclusion levels (40 or 50%) significantly reduced ADC for DM, CP, EE and NFE. In a 90-day growth trial, the replacing of dietary protein by fish silage protein up to 30% of dietary protein in tilapia diet had no significant effect on growth performance including final body weight (BW), body length (BL), condition factor (K), weight gain (WG) and specific growth rate (SGR). The highest replacing levels (40 or 50%) significantly (P<0.001) reduced BW, BL, K, WG and SGR. Results of growth were relatively parallel to those of feed intake, feed conversion ratio (FCR) and protein efficiency ratio (PER) indicating the possibility of replacing 30% of dietary protein by fermented silage in Nile tilapia diets to reduce feed costs, DM and CP contents of the whole fish for the different experimental fish groups were not significantly affected, while EE in the whole fish body was significantly decreased with increasing the inclusion levels of silage in the diets and the opposite trend was observed for ash content. From the economic view, results obtained in the present study indicated the possibility of replacing 30% of dietary protein by silage in tilapia diets without adverse effect on growth or feed utilization parameters and this replacement reduced feed costs/kg diet and feed costs/kg weight gain by 22.43 and 22.02%, respectively.