Fish culture is an important industry where various kinds of marine and freshwater fish are cultured with increase of annual production worldwide. The Philippines has been identified as an increasingly important source of Freshwater eels (Anguilla sp.). Eel is a catadromous fish, which can live in freshwater but spawn in tropical ocean waters. This has a peculiar leptocephalus larval stage that is unique to elopomorph fish. The study evaluates the effect of different levels of Water fern (Azolla filiculoides) extract (AFE) on rearing performance and disease resistance of eel against Aeromonas hydrophila infection.
The extraction of the powdered sample leaves was done through ethanol extraction method. The AFE was supplemented unto one kg formulated feeds; T1-1% AFE (10ml kg-1), T2-2% AFE (20ml kg-1), T3-3% AFE (30ml kg-1), while 0 AFE for the control (C-basal diet). Eel was reared for ten weeks and fed thrice a day at 20% of their average body weight. The weight sampling was done every two weeks. After rearing experiment, the eel was subjected to A. hydrophila infection.
The Wf, WG, and SGR of T2 were increased by 37%, 55% and 61% as compared to that of C, respectively. However, no significant effect was found on FCR among treatments. In addition, percentage survival of C, T1 and T2 were 52%, 46% and 28% higher than that of T3, after ten weeks of rearing, respectively. On the other hand, percentage survival of T2, T1 and T3 were increased by 102%, 48% and 16 % as compared to that of C at three days after A. hydrophila infection, respectively. The improved growth performance and disease resistance could be attributed to the antioxidant capacity (TAS: 1.13 mmol/L; DPPH: 52.61%) and phytochemical constituents (tannins and saponins) of AFE. Overall, AFE at 2% improves rearing performance and disease resistance of eel against A. hydrophila infection.