A review of the bacterial flora of teleosts and elasmobranchs, including methods for its analysis

Techniques for the quantitative and qualitative analysis of the commensal bacterial flora of fish are reviewed. The literature concerning the commensal bacterial flora of fish indicates that teleost skin often features 10²–0⁷ organisms per cm² of skin, representing the following taxa, in descending numerical order, Achromobacter, Pseudomonas, Flavo-bacterium and Cytophaga species also coryneform organisms. Actively feeding teleosts appear to have an alimentary canal bacterial flora similar to that of the skin and gills, often there are from 10³–10⁸ organisms per 1.0 g, wet weight, of tissue. According to the limited data available for elasmobranchs Gram–positive bacteria are the predominant component of the bacterial flora on the skin of sharks, though the bacterial flora of North Sea skate ( Raja spp.) is reported as being similar to that of teleosts. The commensal flora of fish, particularly of teleosts, is related to their environment and is influenced by environmental changes that affect the quality of the water. Regular monitoring of the water of commercial fish ponds and aquaria for bacterial quality, temperature, dissolved oxygen concentration and pH, combined with a base–line knowledge of the water's quality, may provide an advanced indication of the presence of bacteria potentially able to produce diseased conditions, and factors that will enhance their growth.