Characterisation of bacterial communities associated with early stages of intensively reared cod (Gadus morhua) using Denaturing Gradient Gel Electrophoresis (DGGE)

High mortality is often observed during the early life stages of intensively reared cod, and believed to be at least partly caused by opportunistic bacteria. The aim of the present study was to use Denaturing Gradient Gel Electrophoresis (DGGE) of PCR-amplified 16S rDNA to characterise the bacterial populations associated with early life stages of cod larvae in intensive hatcheries. At one hatchery the analysis was carried out during a period of approximately 4 weeks post hatch, and confirmed that cod larvae are associated with bacteria before and after the onset of exogenous feeding. A change in the number of bands and banding positions indicate that new bacteria or bacterial community were introduced between the samples taken at day 5 and 13, probably as a result of the onset of exogenous feeding. The post-feeding analyses were dominated by α-proteobacteria. An additional study from two other hatcheries of moribund fry, were dominated by Vibrio spp., including V. xuii and V. logei. It is concluded that DGGE is a suitable method for characterising bacterial communities in hatcheries. However, other genes than 16S rDNA might be more suitable for the discrimination of closely related taxa, particularly different Vibrio spp.