HETEROGENEITY IN THE DISTRIBUTION OF MITOCHONDRIAL-DNA HAPLOTYPES IN FEMALE RAINBOW-TROUT SPAWNING IN DIFFERENT SEASONS

Analysis of females spawning throughout the year (October to late February) at a commercial fish farm in Ontario, revealed significant heterogeneity in the distribution of their mitochondrial DNA(mtDNA) haplotypes. These findings are consistent with previous data from this stock and indicate that female- daughter spawning times are temporally stable. This suggests a high maternal genetic contribution to this trait. Conversely, no temporal heterogeneity in the spawning times of females with different mtDNA haplotypes was observed in an unselected government (Ontario Ministry of Natural Resources) hatchery stock recently derived from a wild naturalized population. The government hatchery stock is normally spring spawning and has much higher levels of nucleon diversity compared with the cultured stock. Therefore, it appears that only a limited number of family lines within unselected stocks may show the propensity towards greatly accelerated spawning times. Furthermore, associations between spawning time and mtDNA haplotype may only become apparent following several generations of artificial selection.