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A vacuum degassing apparatus was used to subject channel catfish
Ictalurus punctatus (Rafinesque) to sublethal hypoxia for 24, 48 or 72 h. Spleen,
liver, gills, anterior kidney and posterior kidney from the catfish exhibited histopathological
changes that included necrosis, hyperaemia, oedema, haemorrhage,
hyperplasia and hypertrophy. Ofthe organs examined, gills were most affected by
the hypoxic conditions. After 5 days of reacclimatization to normoxic conditions,
channel catfish continued to exhibit histopathological effects of prolonged hypoxia.
Introduction
Fish diseases occur as an end product of interactions between the organism, the
environment and the aetiological agent (Snieszko 1974). Fish reared in intensive
culture are subjected to stressors such as crowding, fluctuating water chemistry, drug
treatments and hauling which affect the ability of the fish to maintain homeostasis.
If the cumulative effect ofthe stresses exceeds the ability ofthe fish to physiologically
adjust, the fish will die. Factors that impose sublethal levels of stress will result in
physiological disorders and predispose the fish to infectious diseases (Wedemeyer &
Wood 1974).
The physiological response of higher vertebrates to stressors has been described
by Selye (1950, 1973) and incorporated into a response classification called the
general adaptation syndrome (G.A.S.). The physiological response to each of the
stages of the G.A.S. is characteristic and varies little from species to species. The
physiological responses are also remarkably independent of the nature of the stressor.
There are many similarities between the metabolic changes seen in stressed fish and
those recognized in higher vertebrates (Hoar 1957). The biochemical and physiological
adjustments initiated through the G.A.S., such as hormonal and neurological
changes, and the morphological alterations resulting from these adjustments, may
serve as valuable indicators when making management decisions concerning fish
health that result in stressful manipulation of fish populations.
Hypoxia (Fry 1969), ammonia, pH, temperature, dissolved solids (Wedemeyer &
Yasutake 1978) as well as other water quality parameters have been recognized as
important stressors of fish. Management practices that maximize fish production in
Correspondence: Mr A. L. Scott, Department of Fisheries and Allied Aquacultures, Agricultui^e
Experiment Station, Auburn University, Auburn, Alabama 36830, U.S.A.
jientific PubHcations 305