Sustained, natural spawning of southern flounder Paralichthys lethostigma
under an extended photothermal regime
W.O.
Watanabe, P.M. Carroll, H.V. Daniels-2001
Journal
of the World Aquaculture Society, 32(2): 153-166 (from Current Contents)
Abstract :
Hormone-induced
spawning of southern flounder Paralichthys lethostigma has produced
substantial numbers of viable eggs, but wide variations in fertilization and
hatch rates have been reported. Recently, sustained natural spawning of
southern flounder broodstock, without hormone induction, has been achieved
in our laboratory. Adults (average weight = 1.12 kg; N = 25), including 6
captured as juveniles in 1993 and 19 captured as adults during September
1998, were stocked in two 4.8-m(3) controlled-environment tanks in October
1998 and held under natural photothermal conditions until January 1999, when
an artificial winter photo-period of 10 L:14 D was initiated and then
maintained through April 1999. Sex ratio was approximately 13 females:g
males:7 unknown. Natural spawning was observed in early December 1998 and
increased in frequency to a peak in March 1999, before declining in late
April. Water temperature ranged from 13.9 to 24.5 C during the spawning
period, Natural spawnings over 142 d produced a total of 18.3 x 10(6) eggs,
with a mean fertilization rate of 28.0% (range = 0-100%), yielding 4.94 x
10(6) fertilized eggs. The mean percentage of eggs that remained buoyant in
full-strength seawater (34 ppt) was 41.3% (0-98%), while hatching rate of
buoyant eggs was 37.3% (0-99%) and survival of yolksac larvae to the
first-feeding stage was 30.2% (0-100%). Gonadal biopsies in late April
identified six females from both tanks as probable spawners. A preliminary
comparison suggests that natural spawning produced much larger numbers of
viable eggs per female, with higher egg quality (i.e,, fertilization and
hatching success) than hormone-induced spawning. In contrast to natural
spawning, hormone-induced strip-spawning enabled timing of spawnings to be
more precisely controlled. These results suggest that a combination of both
natural and hormone-induced spawning of photothermally conditioned fish will
help produce the large numbers of eggs required to support commercial
production.
(Univ
N Carolina, Ctr Marine Sci, 7205 Wrightsville Ave, Wilmington, NC 28403,
USA)