Influence of environmental factors on the ontogeny of the immune system in turbot

Flatfish are of high value in wild fisheries and this has stimulated development of aquaculture for several species (Tilseth, 1990), with production of farmed turbot, Scophthalmus maximus now exceeding 2000 tonnes per annum in Europe (Riaza and Hall, 1993). One factor that limits aquaculture production is microbial infection and extensive losses still occur in the early rearing stages of flatfish culture. The immune response in all fish is regulated by temperature and immunological maturity also appears to be related to size, rather than age. Therefore, factors such as food availability and temperature, which affect the growth of larvae, may affect the development of immune organs and mechanisms, as well as the efficiency of the immune response to respond to pathogens. In aquaculture, flatfish are often reared at temperatures greater than those found in natural waters and it is not known whether this is beneficial, neutral or deleterious to immunocompetence in the fish. Similarly, rising temperatures caused by global climate change may affect the immune competence in flatfish in the wild with consequences for these fisheries. Therefore, this review considers available knowledge of the effect of temperature and other factors on the immune development of turbot larvae and larvae of other relevant species.