Effects of delayed
metamorphosis on larval competence, and postlarval survival and growth of
abalone Haliotis discus hannai
H. Takami, T. Kawamura, Y. Yamashita-2002
Aquaculture, 213(1-4): 311-322
Abstract:
The effects of delayed metamorphosis on larval
competence, and the postlarval survival and growth of Haliotis discus
hannai (H. discus hannai) were examined. Competent larvae were induced
to metamorphose at 5, 10, 15, and 19 days after fertilization by the
addition of 1 µM g-aminobutyric acid (GABA). Larvae in another
group were maintained until individuals metamorphosed spontaneously.
Metamorphosed individuals (postlarvae) were reared in the laboratory at 20
°C fed on a benthic diatom Cylindrotheca closterium or without any
food in equivalent conditions. Metamorphosis, survival, and growth
(determined from shell length) rates were measured. The percentage of
individuals that had metamorphosed 2 days after the addition of GABA
increased with the length of larval swimming period; larvae that were 5 and
19 days old when induced to metamorphose showed 19% (±5.6; S.E.) and 96% (±3.6)
metamorphosis, respectively. The percentage of postlarvae that metamorphosed
spontaneously increased after 17 days from fertilization and reached 96% (±3.0)
at 24 days postfertilization. Survival rates of fed postlarvae depended on
larval swimming period. For larvae that swam for </= 15 days, more than
80% of postlarvae survived throughout the 20-day experimental period. In
contrast, the survival rate was only 57% (±2.9) for 19-day-old larvae.
Postlarval growth rates did not differ significantly between larval swimming
periods </= 15 days. However, the growth rate of postlarvae from
19-day-old larvae was significantly lower than that of </= 15-day-old
larvae. In the starved treatments, survival rate was lower, and the final
shell length of the dead animals was less, as larval period became longer.
(Tohoku National Fisheries Research Institute, 3-27-5
Shinhama, Shiogama, Miyagi 985-0001, Japan, e-mail: htakami@affrc.go.jp)