GENETIC-IMPROVEMENT OF DISEASE RESISTANCE IN FISH - AN OVERVIEW

It is of great importance to increase the natural disease resistance o f farmed fish. Response to direct selection for increased survival in commercial environments has been low, basically due to inaccurate reco rds of the trait. However, challenge tests with family groups which we re infected with specific pathogens showed significant genetic variati on in mortality, indicating that improvement by selection i s possible . Several studies have shown a significant positive genetic correlatio n between growth rate and survival. Therefore survival would be expect ed to increase as a correlated response when selecting for growth rate . Significant genetic variation has been found in immunological parame ters, but more knowledge is needed about the genetic correlations betw een these parameters and survival before indirect selection for increa sed survival can be applied. Heterosis for survival has not shown larg e effects. However, it may be still of interest to develop resistant l ines to specific diseases and cross them to produce hybrids. Disease r esistance genes have not been identified in fish. However, the product ion of transgenic fish with enhanced resistance to specific diseases r emains as a possibility for the future.