Responses to two-way selection on growth in mass-spawned F₁ progeny of Argopecten irradians concentricus (Say)

In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop (Argopecten irradians concentricus) was examined to evaluate the efficacy of a selection program currently being carried out in Beibu Bay in the South China Sea. A total of 146 adult scallops were randomly selected from the same cultured population of A. i. concentricus, and divided into two groups in shell length (anterior-posterior measurement): large (4.91–6.02 cm, n=74) and small (3.31–4.18 cm, n=72). At the same time, a control group was also randomly sampled (4.21–4.88 cm, n =80). Mass-spawned F 1 progenies from the three size groups were obtained and reared under identical conditions at all growth phases. The effects of two-way (or upward-downward) selection on fertilization rate, hatching rate, survival rate, daily growth in shell length and body weight were assessed in the three size groups. Results show that significant differences (P<0.01) were found in hatching rate, survival rate and daily growth of F₁ progenies, but not in fertilization rate (P>0.05), among the three groups. The hatching rate, survival rate and daily growth of the progeny of large-sized parents were greater than those of the control group (P<0.05), which in turn were larger than those of small-sized group (P<0.05). Responses to selection by shell length and body weight were 0.32 ± 0.04 cm and 2.18 ± 0.05 g, respectively, for the upward selection, and −0.14 ± 0.03 cm and −2.77 ± 0.06 g, respectively, for the downward selection. The realized heritability estimates of shell length and body weight were 0.38 ± 0.06 cm and 0.22 ± 0.07 g for the upward selection, and 0.24 ± 0.06 cm and 0.37 ± 0.09 g for the downward selection, respectively. The change in growth by bidirectional selection suggests that high genetic variation may be present in the cultured bay scallop population in China.