Improved breeding for disease resistant strain of fugu following whole genome sequencing

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The fugu Takifugu rubripes is the only economic species among the fishes with genomes that have been sequenced. The aim of this study was to establish the strategy for the improved breeding for disease resistant strain of this species utilizing genome sequences.1. Search for immune factorsUsing homology searches, we succeeded to find many genes which are related to the immune reaction, such as B-cell and T-cell related factors, cytokines, chemokines, complement factors, and lectins. We are now able to make further investigations of immune response against the parasite, since this fish has a large body size that enables us to analyze proteins as well as cells related to immunity.2. Genetic linkage map.Since the fugu genome database is composed of highly fragmented sequences, we needed to make a genetic linkage map for the genetic research of this species. We have constructed the linkage map containing 1219microsatellite loci that provide anchor points to the 86% of the genome assembly.3. QTL analyses for resistance/susceptibility against a parasite, Heterobothrium okamotoi.One of the biggest problems for fugu culture is a parasite Heterobothrium okamoti, which cause anaemia by taking blood at the gill. Establishment of the linkage map enabled us to conduct QTL analysis of molecules related to disease resistance, although strains of this species are quite limited. We used inter species hybrid with Kusa-fugu, T. niphobles, which is resistant against the parasite. F2 generation showed wide individual variations in the resistance/susceptibility against the parasite. By QTL analysis, we found each two loci of parasite number and parasite growth. Further extensive research will lead to determination of the genes.