Quantitative and qualitative studies of the bacterial microflora of turbot, Scophthalmus maximus L., gills

Populations of aerobic heterotrophic bacteria, occurring on the gills of healthy turbot, were estimated using a dilution plate technique. From a comparison of 18 media, the highest counts, i.e. 7.0 × l0⁵ g⁻¹, were obtained after incubation at 15–25°C on a specifically formulated medium which contained low quantities of beef extract, casein, tryptone and yeast extract. These bacteria were equated with Asticacaulis sp., Hyphomicrobium sp., Janthinobacterium lividum, Prosthecomicrobium sp., Pseudomonas fluorescens and Vibrio sp. Evidence from scanning electron microscopy pointed to a general lack of intimate colonization of exposed areas of the gill. Instead, micro-organisms colonized protected niches, such as the clefts between lamellae and in secluded areas on the arches.