Effects of fermented soy pulp (Okara) on the growth performance and histopathological changes of red hybrid tilapia (Oreochromis sp.)

Abstract

This study evaluated the effect of fermented soy pulp (FSP) as a partial substitute for fish meal (FM) in the diet of red hybrid tilapia (Oreochromis sp.) on the fish's growth performance via feeding assessment. The feeding trial was conducted for 56 days (eight weeks) based on five dietary treatments at varying proportions of FM and FSP (T1: 50% FSP, 30% FM; T2: 60% FSP, 20% FM; T3: 70% FSP, 10% FM; T4: 75% FSP, 5% FM; T5: 80% FSP, 0% FM), with the commercial pellet (Starfeed) serving as control. Chemical analyses showed that both T1 and T3 had the highest protein content (18.1%). Meanwhile, the control group showed the best performance in terms of specific growth rate (SGR) and feed conversion ratio (FCR), and these values were significantly different (p < 0.05) from the five dietary treatments. In contrast, the survival rate of T1 group (82.5%) was comparable to the control group (85.0%). All the dietary treatments showed histological changes in fish liver: < 25% changes for T1, T2, and T3, whereas < 50% changes in T4 and T5. However, the control group did not exhibit any histological changes in the liver. Therefore, FSP is recommended as a dietary supplement for red hybrid tilapia.