Interactions between fish larvae and bacteria in marine aquaculture

Modem aquaculture provides effective means for intensive seafood production under "controllable" conditions. This rapidly growing industry, however, h as experienced relatively severe disease problems owing to lack of control of the microbiota. in rearing systems, Disease control is an inherent part of any intensive animal production system; however, in the aquatic environm ent, the intimate relationship between bacteria and their host and the freq uent use of open production systems adds to this challenge. The use of anti biotics in aquatic ecosystems is presently kept to a minimum, and fortunate ly, vaccines and other health control means have so far kept most diseases under relative control. Various organisms, however, may not respond to vacc ines, and new diseases or variants are a constant challenge to the industry . In aquaculture, eggs are kept in incubators with a microflora that differ s considerably from that in the sea, and become heavily overgrown with bact eria within hours after fertilisation. Fish larvae ingest bacteria by drink ing and are, thus, primed with antigens before active feeding commences. Th is may result in the formation of an indigenous larval microflora; however, at present, we know little about this process. The microflora of marine in vertebrates may harbour bacteria that are pathogenic to other organisms and , thus, invertebrate co-inhabitants or food organisms in aquaculture may se rve as vectors for transfection of fish pathogens. In intensive egg product ion and larviculture, the numbers of bacteria are kept low by various forms of water treatment and disinfection. These approaches, however, may distur b the balance between microbial communities, or favour proliferation of opp ortunistic bacteria or unpredictable development of bacterial communities. Thus, there is a need for better microbial control during intensive larval production. The use of probiotics has proven advantageous in domestic anima l production, and microbial management may also have a potential in aquacul ture. Better control of host-microbe interactions is a prerequisite for sta ble production of marine larvae in intensive systems. (C) 2001 Elsevier Sci ence B.V. All rights reserved.