Gastrointestinal bacteria in Rohu, Labeo rohita (Actinopterygii: Cypriniformes: Cyprinidae): scanning electron microscopy and bacteriological study.

The gut microbiota of marine and freshwater fish has been widely investigated during the last two decades (Cahill 1990, Ringø et al. 1995, Hansen and Olafsen 1999, Ringø and Birkbeck 1999, Ghosh et al. 2002a, Saha et al. 2006). It is a consensus view that dense bacterial population levels occurs in the gastrointestinal (GI) tract of fish (Austin 2002), and the gut microbiota can be defined as either autochthonous (indigenous) or allochtonous (transient) depending upon its ability to adhere and colonize the mucus layer in the digestive tract (Ringø and Birkbeck 1999, Ringø et al. 2003, 2007). Previous studies have isolated different bacteria species from the gut of one of the Indian major carps—rohu, Labeo rohita (Hamilton, 1822) and it has been suggested that the gut microbiota might be beneficial in the nutrition of the fish (Ghosh et al. 2002a, Kar and Ghosh 2008, Ray et al. 2010). Furthermore, attempts have also been made to use beneficial gut bacilli originally isolated from rohu as the probiotics for the fish (Ghosh et al. 2002b, 2003). One of the major criteria for selecting a probiotic strain is its ability to adhere and ACTA ICHTHYOLOGICA ET PISCATORIA (2010) 40 (2): 129–135 DOI: 10.3750/AIP2010.40.2.05