Annual Research & Review in Biology

Dietary Spirulina is increasingly examined as a feed ingredient in aquaculture, but the response of butter catfish to graded supplementation requires species-specific evaluation. This study assessed serum lysozyme activity and intestinal amylase and protease responses in Ompok bimaculatus following a 60-day feeding trial. Five experimental diets contained 0% (control), 10%, 15%, 20% or 25% Spirulina platensis. Serum lysozyme activity was determined using a turbidimetric assay with Micrococcus lysodeikticus as the substrate, whereas intestinal enzyme responses were assessed spectrophotometrically. The measured responses increased progressively with dietary inclusion. At the end of the lysozyme assay, activity was approximately 2 U/mL in the control and 18, 35, 52 and 69 U/mL in the respective supplemented groups. The 25% group therefore showed a 34.5-fold higher lysozyme activity than the control. Calculated amylase concentrations were 1.64, 4.08, 4.95, 6.11 and 7.07 mg/mL across the five dietary groups. The corresponding calculated protease values were 4.71, 8.79, 9.95, 12.36 and 13.37. Among the tested diets, 25% Spirulina produced the highest measured lysozyme, amylase and protease responses. These findings indicate an association between increasing dietary Spirulina inclusion and the measured immune-related and digestive enzyme responses. Because the biochemical measurements do not establish growth performance, nutrient digestibility or disease resistance, further investigation is needed to determine the optimal dietary inclusion level for O. bimaculatus.