Effects of dried microalgal supplement on molting efficacy, enzyme activity and histological improvement in freshwater prawn (Macrobrachium rosenbergii) larval development: a comprehensive study

This research, pioneering in its nature, examined the impact of microalgal supplements on the larval developmental processes and mass production of Freshwater Prawn (Macrobrachium rosenbergii) post-larvae (PL) on a commercial scale. Overcoming the obstacles to prawn PL production in Bangladesh since 2011 was a major focus of our initiative. A total of six cemented tanks, each with a capacity of 3000 liters, were used for the two treatments and a control group in replicates. In Treatment 1 (T1), microalgal (powder) supplementation as nutritional source was administered at a concentration of 4 ppm, consisting of 2 ppm of spirulina powder (SP) and 2 ppm of black algae powder (BAP), four times daily; conversely, Treatment 2 (T2) received the identical dosage six times daily. The control tank (C) did not receive any algal supplementation. PL production, survival rate, digestive enzyme activities, superoxidase dismutase (SOD) activity and histological changes in the hepatopancreas and mussel of the larvae were evaluated to determine the efficacy of the treatments. Approximately, 87,000 freshly hatched larvae were stocked in each tank. Significantly higher (p < 0.05) PL production was found in T2 followed by T1and C. Analogously, a substantially higher survival rate was recorded in T2 (93.59±2.82%) followed by T1 (86.28±3.58%) and C (62.42±0.75%). Amylase enzyme activity was significantly higher (p < 0.05) in T2 followed by T1 and C. Protease and lipase enzyme activity were significantly higher (p < 0.05) in the treatments than the control, however, no significant difference within the treatments was observed. In contrast, SOD activity recorded significantly higher (p < 0.05) in the control than the treatments. Histological evaluations of the hepatopancreas and muscle tissues indicated improved organization and health conditions in PL from treatment tanks, contrasting with irregular distribution and less organized muscles in control PL. The study found that applying 4 ppm microalgae (SP+BAP) 6 times a day can significantly increase healthy PL production in prawn hatcheries.