Intestinal microflora of fish larvae and fry

It is well known that microorganisms cannot be avoided in commercial aquaculture. The skin, gills and gastrointestinal tract are inhabited by microorganisms which are especially adapted to a life in intimate contact with these body surfaces, Microflora associated with the gastrointestinal tract of the early life stages of fish larvae and fry have been described in several investigations, but the establishment of a balanced gut nora in fish larvae is complex, and seems to be influenced by the microflora of the egg, the live feed and the bacteria present in the tank water, Generally, the gut of newly hatched larvae contains very few bacteria, but it is rapidly colonized during the first few days in a two-step pattern. The existence of an intestinal microflora in larvae has led to the assumption that some microorganisms are normal (autochthonous), while others are regarded as abnormal and may lead to disease. The disease conditions known in larviculture are closely related to the particular ecological strategies of the pathogens, as well as to the species and development stage of the fish. The introduction of beneficial, or probiotic bacteria into the larval gut could be done using rotifers as carriers or by inoculation of the rearing water with live bacteria, The seeding of the gut with harmless bacteria which occupy the attachment sites may prevent infection by pathogenic bacteria.