EFFECT OF AEROBIC MICROBIAL FLOC ON HETEROTROPHIC BACTERIAL ABUNDANCE IN INTENSIVE NURSERY REARING OF GIFT TILAPIA

The health of fish is regulated by gut microbes which maintains a homeostasis between autochthonous or allochthonous bacteria. The chief sources of allochthonous gut microbiota are rearing medium and nutrition which interact with autochthonous gut microbiota and forms the microbial community. Hence, the characterization is used to visualize and confirm the heterotrophic and pathogenic bacteria activity in aquatic habitats and fish guts. However, ingested microbes and the similarity of gut microbes are still poorly understood in aerobic microbial floc system.

The experiment was conducted in outdoor lined pond (10 × 10 × 1m ) with Aerobic Microbial Floc (AMF) as treatment and without Aerobic Microbial Floc (non- AMF) as control. GIFT tilapia seed were stocked at the rate of 50 numbers /m² (0.2054  0.02 g/fry) in treatment as well as control.  In the treatment, spent wash was used as carbon source to develop aerobic microbial floc with a C/N ratio of 10:1.

The study conducted for a period of 30 days and assessed the water quality, microbial community and pathogen control. Bacterial community of culture water and gut microbial count was observed at 7 days interval. The level of heterotrophic bacteria with different genus was continuously triggered in culture water as well as gut flora of tilapia reared in AMF based system. Among the heterotrophic bacterial group, Bacillus count was significantly (P<0.001) increased in AMF culture water (4.1 x 10¹ ± 0.1 x 10¹ CFU/ml) than control (absent). However, the pathogenic bacterial group populations such as Aeromonas sp (1.07 x 10³ ± 5 x 10¹ CFU/ml), Vibrio sp. (2.3 x 10² ± 1 x 10¹ CFU/ml) and Total coliform (1 x 10³ ± 1 x 10¹ CFU/ml) count were decreased in AMF based culture water due to the presence of Bacillus sp. performed the antagonistic or probiotic effect. The presence of beneficial microorganisms improved the water quality by reducing toxic nutrients. The present study demonstrated that, bacterial community in fish gut was more similar to culture water and proved the potential of AMF promoting beneficial microbes (figure 1) and suppressing harmful microbes.