Physiological performance of
juvenile southern flounder, Paralichthys lethostigma (Jordan and
Gilbert, 1884), in chronic and episodic hypoxia
J.C. Taylor, J.M. Miller-2001
Journal of Experimental Marine Biology and Ecology,
258(2): 195-214
Abstract:
Dissolved oxygen (DO) is proving to be one of the
most important abiotic factors determining growth and survival of juvenile
estuarine fish. In shallow, throughout estuarine systems, low DO can occur
in two broad categories: a diel oscillating pattern resulting in repeated
nocturnal hypoxia due to the photosynthesis-respiration cycle of algal
populations, or as prolonged bottom water hypoxia or anoxia caused by
stratification. A series of laboratory experiments was conducted to
characterize the physiological performance of juvenile southern flounder, Paralichthys
lethostigma, (55-65 mm TL) exposed to four treatments of DO: (1)
constant normoxia (6.50±0.50 mg O2 l-1), (2) constant
hypoxia (2.79±0.19 mg O2 l-1), (3) constant
intermediate hypoxia (4.74±0.18 mg O2 l-1), and (4)
an oscillating oxygen environment cycling dielly between the normoxic and
hypoxic levels (2.8-6.2 mg O2 l-1, daily mean=4.40 mg
O2 l-1). Routine respiration was positively correlated
with DO level and increased significantly during the day in the oscillating
treatment in response to increasing DO. Ventilation rates were negatively
correlated with the DO level in the constant treatments and increased
significantly at night in the oscillating treatment in response to nocturnal
hypoxia. Similarly, hematocrit levels were negatively related to DO levels
in the constant treatments after 5 and 26 days of exposure to the
treatments. Hematocrit levels also increased significantly the oscillating
treatment, apparently in response to the episodic nocturnal hypoxia. Growth
was significantly reduced in the 2.8 mg O2 l-1
treatment and the oscillating treatment but not in the 4.7 mg O2
l-1 treatment. Acclimation was evident by an increase in growth
rates from week 2 to week 3 and a decrease in hematocrit levels between 5
and 26 days of exposure in the 2.7 and 4.5 mg O2 l-1
treatments but was not evident in the normoxic or oscillating treatments.
These results suggest that a juvenile fish must remain in even moderately
low DO in order for acclimation to occur. The research presented
demonstrates that correctly assessing habitat quality in terms of DO
requires knowledge of a fish's physiological and environmental history.
(Department of Zoology, Campus Box 7617, North
Carolina State University, Raleigh, NC, 27695, USA, Tel.: +1-252-222-6322;
fax: +1-252-222-6311, e-mail: Chris_Taylor@ncsu.edu)