Can Azolla filiculoides be a complementary feed resource for ecological intensification in small-scale fish farming? Biological effects on giant gourami (Osphronemus goramy)

Juveniles of giant gourami Osphronemus goramy Lacépède (1801) were fed for six weeks with different proportions of fresh Azolla (A100% B56% C26% and D0% of replacement). The condition factor (K Fulton ) somatic and immunological indicators were measured. Effects of Azolla on transport stress and bacterial infection with Aeromonas hydrophila were also assessed. Results showed that K Fulton decreased with increasing proportions of Azolla in the diet ( p  < 0.001). Total protein, albumin and globulin in fish fed exclusively with Azolla (treatment A) were significantly lower than in the other treatments. A significant decrease in lymphocytes was observed in treatments A and B ( p  < 0.001) and fish from these treatments had significantly higher levels of monocytes ( p  < 0.001). Neutrophils were significantly higher in treatment A only ( p  = 0.012). Plasma lysozyme levels and serum bactericidal activity increased significantly with Azolla in the diet (both p  < 0.001). Before transport stress, blood glycaemia was significantly lower in fish from treatment A ( p  < 0.001), after transport, glycaemia increased significantly only in treatments B, C and D ( p  < 0.001) and fifteen days after, survival was significantly higher in fish from treatment A. One week after experimental infection the survival of fish from treatments A and B was significantly higher than for fish from treatments C and D ( p  < 0.001). Results suggest that A. filiculoides has positive effects on fish immunological indicators, and resistance to stress and disease but decreases growth performance. We recommend that the replacement of commercial pellets with A. filiculoides should not exceed 30%.