Abstract |
The stress response in fish varies between different species, as well as
between different environmental conditions within the same species. In this context,
the stress response of two teleost species, European sea bass, Dicentrarchus labrax,
and meagre, Argyrosomus regius, species that share some common ecological
features, such as tolerance to changes in salinity, temperature and oxygen levels, but
differ in the baseline and peak plasma values of some commonly used stress
indicators, such as cortisol, glucose and lactate concentration. The working hypothesis
was that the observed differences were related to metabolic discrepancies between
these two species.
Fish reared in net pen sea cages were used, with samplings taking place in
three different seasons, with different sea temperature and differences in the
physiological condition of the fish. Furthermore, a study of the kinetics of the stress
response was conducted in these two species, focusing in the changes in the glycogen
concentration of liver and muscle and the alterations of blood and muscle pH levels.
Moreover, since sea bass shows high baseline concentrations of cortisol, as
well as intense stress response, the study of the functionality of the Hypothalamus-
Pituitary-Interrenal (HPI) axis was conducted via the dexamethasone suppression test,
which is widely used in mammals for research and diagnostic reasons.
The results showed that sea bass had higher carbohydrate energy reserves than
meagre, as well as higher capacity for oxygen transport to the tissues. It also utilized
the anaerobic metabolism in a higher degree. Furthermore, sea bass had higher
cortisol concentration than meagre, both in control and stress fish, and in every
environmental temperature.
Between the different temperatures the pattern of the stress response was the
same for some of the studied hematological and biochemical features, while it
differed in some other.Dexamethasone suppressed cortisol levels to 25%-50% of the initial
concentration, depending on the dose, 24 h after the injection. In contrast, it wasn’t
able to suppress cortisol 4 h after the injection, probably due to the already increased,
by the handling, levels of the hormone. Dexamethasone also led to a slight
hyperglycemia, as well as blood alkalosis and decreased levels of haematocrit.
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