Ontogenic
changes in various stress tolerances of larval and juvenile red sea bream
Pagrus major
Y.
Ishibashi, M. Ozawa, H. Hirata, H. Kumai-2003
Nippon
Suisan Gakkaishi, 69(1): 36-43 (from
ISI Current Contents)
Abstract:
Changes in tolerances to certain environmental stressors, e.g., low and high
temperatures and salinity as well as high concentrations of ammonia, were
studied in the red sea bream Pagrus major during its early life stage up to
42 days post-hatch. Relative tolerance was assessed by determining 24-h
median lethal level. In laboratory experiments, metamorphosis was observed
mainly from days 14-21, and the morphological shift from larva to juvenile
was indicated at 9.5 mm total length at 28 days post-hatch. Among the stages
tested, larva immediately after hatching showed maximum tolerance to all
stressors. Tolerances to both low and high temperatures decreased up to 14
days post-hatch and increased thereafter. Hypo- and hyper-salinity
tolerances also decreased up to the 14(th) day post-hatch and then showed a
gentle increase. In regard to ammonia tolerance, the 50% lethal
concentration diminished drastically between days 2 and 7, showed the lowest
level on day 21, and subsequently rose. These results indicate that, in red
sea bream under these experimental conditions, all tolerances to
temperature, salinity, and ammonia stress temporarily fell during
metamorphosis from days 14-21. It is considered that the depression of the
scope for activity based on increasing oxygen consumption induced the
decrease in various stress tolerances during metamorphosis. It is also
suggested that the 50% lethal levels of various environmental stressors can
be used as a stress test to evaluate the hardiness of a hatchery-produced
red sea bream.
(Kinki
Univ., Sch. Agr. Dept. Fisheries, Nara 6318505, Japan, e-mail: isibasi@nara.kindai.ac.jp)