| Abstract |
The aim of the present study was to develop and evaluate reliable stress indicators in the red porgy, Pagrus pagrus. Specific objectives were (i) to develop a radioimmunoassay for the determination of cortisol, (ii) to evaluate a commercial assay for the determination of catecholamines (Epinephrine and Norepinephrine), (iii) to develop new indicators of acute and chronic stress (prothrombin time, skin colour and concentration of melanin in the skin), and (iv) set baseline values for all stress indicators. The first experiment concerned the evaluation of the use of two anesthetics, 2-phenoxyethanol and clove oil. 2-phenoxyethanol was found to be the most convenient anesthetic for red porgy. The second experiment was to define the response of red porgy to acute (capture and exposure to the air for 3min) and chronic stressors (different stocking density: 5 vs. 25kg/m3; and different water temperatures: 15-19-25oC). Cortisol and lactate were found to be reliable stress indicators of acute stress, presenting elevated concentrations for the first two hours after exposure to the stress stimuli and been declined to resting values after 24h. Catecholamines, glucose, electrolytes, and prothrombin time were also found to be reliable indicators for acute stress, whereas catecholamines, lactate, skin colour and concentration of melanin in the skin, were found to be reliable indicators for chronic stress. Skin colour also exhibited a remarkable relationship with chronic stress with skin being brighter (L*) in non anesthetized fish and in individuals acclimated in 19oC water temperature. Baseline values were determined as follow: Glucose, 2.01-5.21 mmole L-1; Lactate, 0.09-1.95 mmol L-1; Epinephrine, 0.39-5.61 ng ml-1; Norepinephrine, 1.37-9.77 ng ml-1; Cortisol, 0.95-22.93 ng ml-1; K+, 2.00-4.51 mmole L-1; Na+, 166.96-196.17 mmole L-1, Osmotic pressure, 288.4-302.4 mOsm Kg-1, and Prothrombin time, 6.78-17.44 sec. The present study also revealed that density by means of kg/m3, is not an appropriate term to describe the physiological condition of fish (stress). Relative volume, i.e. the volume that the population of the fish occupy within the total water volume, seems to be more appropriate to describe the social interactions between individuals, and thus the stress response. In addition, water temperature (15 and 25 oC) is an important environmental stressor for Pagrus pagrus, as shown by the elevated of catecholamines and lactate concentrations in plasma.
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Ανάπτυξη και αξιολόγηση νέων δεικτών εκτίμησης της καταπόνησης στο φαγκρί
