AN AFLP-BASED CATFISH GENETIC LINKAGE MAP AND QTL DETECTION FOR GROWTH RATE AND DISEASE RESISTANCE

Department of Fisheries and Allied Aquacultures, and Program of Cell and Molecular Biosciences, 203 Swingle Hall, Auburn University, Auburn, AL 36849

Catfish is the most important cultured aquaculture species accounting for over 50% of the aquacultural production in the US. Important performance traits include growth rate, disease resistance to enteric septicemia of catfish (ESC) and columnaris disease, feed conversion efficiency, processing yields, tolerance to low dissolved oxygen, tolerance to high ammonia, and harvestability. The aim of this work was to construct a genetic linkage map containing QTLs for the most important performance traits. To date, 607 AFLP markers have been genotyped in 71 fish derived from F1 hybrid (channel catfish x blue catfish) backcrossed with blue catfish female. The segregating markers thus were channel catfish markers heterozygous in the F1 hybrid catfish. Over 94% of the markers were linked markers and were assigned into linkage groups. It appears that a large proportion of AFLP markers is highly clustered. With the large number of AFLP markers analyzed, however, we were able to have a broad genomic coverage. It appears several AFLP markers are linked to the performance traits of growth rate, resistance to ESC, and resistance to columnaris. However, additional fish are being tested to evaluate the linkage and chromosomal regions containing quantitative trait loci (QTLs) responsible for the performance traits. Genotyping of reciprocal backcross (F1 backcrossed with channel catfish male) progenies has also been conducted to construct the linkage map of blue catfish, which can be anchored by the shared markers with the channel catfish. This will provide information concerning genomic evolution and conservation, difference between the male and the female linkage maps, and more importantly, the QTLs from the blue catfish. Blue catfish is much more resistant to ESC disease than channel catfish. Therefore, analysis of QTLs with relation to the linkage map is the first step to identify the blue catfish genomic regions for genetic improvement through introgression.