Effects
of light intensity and salinity on growth, survival, and whole-body
osmolality of larval southern flounder Paralichthys lethostigma
J.P. Henne, W.M. Watanabe-2003
Journal
of the World Aquaculture Society, 34(4): 450-465 (from ISI Current Contents)
Abstract:
The southern flounder Paralichthys lethostigma is a high-valued flatfish
found in estuarine and shelf waters of the south Atlantic and Gulf coasts of
the United States. Wide temperature and salinity tolerances exhibited by
juveniles and adults make it a versatile new candidate for commercial
culture, and studies are underway in the southeastern U.S. to develop
hatchery methods for this species. The objectives of this study were to
establish illumination and salinity conditions that optimize growth and
survival of larval southern flounder reared through the yolk-sac and first
feeding stages to 15-d post-hatching (15 dph). Early embryos were stocked
into black 15-L tanks under light intensities of 5, 50, 100, and 1,000 Ix
and at salinities of 24 and 34 ppt in a 4 x 2 factorial design. Significant
(P < 0.05) effects of both light intensity and salinity on growth and
survival were obtained, with no interaction between these effects. On 11 dph
and 15 dph, growth was generally maximized at the intermediate light
intensities (50 and 100 lx) and minimized at the extremes (5 and 1,000 lx).
By 15 dph, growth was higher at 34 ppt than at 24 ppt. Survival to 15 dph
showed trends similar to those of growth. Survival was higher at 100 lx
(avg. = 46%, range = 41-54%) than at 5 lx (avg. = 11%, range = 6-17%) and
higher at 34 ppt (avg. = 43%, range = 31-55%) than at 24 ppt (avg. = 17%,
range = 8-38%). Whole-body osmolality (mOsmol/kg) was significantly lower in
larvae reared at 24 ppt (avg. = 304, range = 285-325) through 11 dph than in
larvae reared at 34 ppt (avg. = 343, range = 296-405). Larvae reared under
the extreme light intensity treatments (5 and 1,000 lx) at 34 ppt appeared
to exhibit osmoregulatory stress, particularly on 11 dph, when a marked
increase in whole-body osmolality was observed. The mid-intensity treatments
(50 and 100 lx) at 34 ppt optimized growth and survival of larval southern
flounder in this study; and elicited the most stable osmotic response. These
conditions appear to be consistent with those that southern flounder larvae
encounter in nature during this early developmental period.
(US Fish & Wildlife Serv., Bears Bluff Natl. Fish
Hatchery, POB 69, Wadmalaw Isl. SC29487, USA)