EFFECTS OF INBREEDING DEPRESSION IN PACIFIC ABALONE HALIOTIS DISCUS HANNAI

To demonstrate inbreeding depression in various traits of Pacific abalone Haliotis discus hannai, 12 inbreeding full-sib families (brother sister mating) and 13 outbreeding full-sib families were produced by factorial mating using the parents from two full-sib families. All 25 full-sib families were reared for 158 days after settlement, and 8 of the inbred and outbred full-sib families were reared until 3 y 4 mo of age. Inbreeding depression traits between inbred and outbred crosses were compared. No significant differences in fertilization rate, hatchability, and veliger survival rate were observed between the inbreeding and outbreeding crosses. Deformity rate in veliger larvae from the inbred crosses was significantly higher than that among the outbred crosses (t-test, P < 0.01). Significantly lower survival rates were observed in the inbreeding crosses at 109 days after settlement (t-test, P < 0.01) and between I y 4 mo-old and 3 y 4 mo-old crosses (t-test, P < 0.05). Mean increases in shell length were not different between the inbred and outbred crosses. Gonad indexes in both crosses were investigated in 3 y 4 mo-old families. The gonad index among inbreeding crosses was significantly lower than that of the outbreeding crosses (analysis of covariance: df =1, SS = 13.141, F = 25.834, P < 0.01). Significant inbreeding depression in larval deformity rate, juvenile and adult survival rates, and gonad index of Pacific abalone was detected. Although only 2 full-sib families were used as parental broodstock, this is the first lone-term rearing examination, from fertilization to adult, of inbreeding depression in Pacific abalone.