Replacement of Fish Meal with Fermented Fish Offal Silage in the Diet of the Nile tilapia (Oreochromis niloticus)

This study evaluated the potential of fermented fish offal silage as a protein source for the Nile tilapia (Oreochromis niloticus) fry. The silage was made from minced fish offal, 15% molasses, and 5% yogurt, and was stored for 35 days. During storage, the pH was stabilized at 4.30, maintaining good organoleptic characteristics, with a dark brown color and a pleasant malty aroma, showing no signs of spoilage. The dried silage contained 13.03 ± 0.89% protein, 41.9 ± 0.35% fat, 3.99 ± 0.43% ash, and 6.92 ± 0.53% moisture. Levels of non-protein nitrogen, total volatile base nitrogen, peroxide value, and free fatty acids were within acceptable limits. The silage was deemed microbially safe, with pathogens either below risk levels or absent. Three isoproteinous and isocaloric diets were formulated with 60, 80, and 100% of fermented fish offal silage replacing fish meal and were fed for O. niloticus fry for 27 days in a feeding trial. The best growth of fish occurred at the lowest inclusion level (60%) offal silage diet (FFO 60) yielding weight of 4.53g and length of 6.01cm. The length-weight relationship revealed a positive allometric growth. The 80% replacement of fish meal resulted in the lowest mean weight gain (4.12 ± 0.11g), while the 60 and 100% replacements yielded better mean weight gains compared to the reference diet, i.e., 4.27 ± 0.48g and 4.23 ± 0.25g, respectively. The cost of the reference diet for 1kg of weight gain was the highest at Tk 102.80/kg, followed by the lowest inclusion level of fermented fish offal silage diet (FFO 60) at Tk 72.16/kg. This study suggested that fish offal silage can replace up to 60% of fish meal in the diet of O. niloticus fry without any retardation of growth, no significant changes in carcass protein, and at a reduced cost.