Studies on relations of bacteria with skin surface of Carassius auratus L. and Poeciloia reticulata

Inocula taken from body surfaces of goldfish and guppy indicated the presence of a variety of aquatic bacteria. However, bacteria were not seen when skin samples were studied by means of histology and scanning electron microscopy. Skin from the body flank was essentially a barren field of Malpighian cell surfaces, interrupted occasionally by goblet cell secretions. Under experimental conditions, Aeromonas hydrophila (Gram‐negative, motile rod) attached in large numbers to the dermal surface of artificially made wounds in goldfish, but none was found on adjacent Malpighian cells. Freshly collected skin secretions from goldfish did not influence survival or growth of A. hydrophila in vitro . The study concludes that, under normal conditions, cuticle overlying the Malpighian cells prevents firm attachment and colonization of the skin by aquatic bacteria. It is argued that bacteria isolated by microbiological studies were simply in suspension near the body surface.