Exploration of marine red seaweed as a dietary fish meal replacement and its potentiality on growth, hematological, biochemical, and enzyme activity in freshwater fish Labeo rohita.

The present study investigated the dietary fishmeal replacement by marine red seaweed (Halymenia dilatata) meal (RSM) on growth performance, feed utilization, chemical body composition, hematological constituents, digestive, antioxidant, and metabolic enzymes in freshwater fish Labeo rohita (Rohu) fingerlings. The fish were fed with RSM-free control diet (RSM0) and four experimental diets, which replaced fish meal (FM) with varying levels of RSM (25%, 50%, 75%, and 100%, represented as RSM25, RSM50, RSM75, and RSM100 respectively). After a 60-day feeding trial, the survival rate (SR), growth performance (length gain, weight gain, and specific growth rate), protein efficiency ratio, chemical body composition (protein, lipid, and ash), and digestive enzymes (amylase and protease) were significantly increased (P < 0.05) in the fish fed with RSM50 diet containing 39% protein level. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a higher staining intensity of muscle proteins in fish fed with the RSM50 diet. However, the hematological constituents (hemoglobin, hematocrit, red blood cell, white blood cell, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration), antioxidant enzyme - superoxide dismutase, and metabolic enzymes (glutamic oxaloacetic transaminase and glutamic pyruvic transaminase) were not significantly altered in RSM50 diet when compared to control. In contrast, hematological constituents were decreased (P < 0.05), and antioxidant and metabolic enzymes were increased in rohu fed with RSM75 and RSM100 (P < 0.05). Furthermore, these findings suggest that RSM might be adopted at a pace of 37% (estimated polynomial second-order regression) and is found to be beneficial for freshwater fish L. rohita diets that enhance growth and immune responses. The current study recommended substituting (50%) of marine red seaweed (Halymenia dilatata) for fish meal significantly improves the growth performance, chemical body composition, and digestive enzymes of L. rohita and this could be a valuable natural replacement for fishmeal to reduce the production cost of aquatic feed.