M. Pavlidis

Background colour influence on the stress response in cultured red porgy Pagrus pagrus

Red porgy Pagrus pagrus were placed and maintained in white, grey and black background fibreglass tanks for 2 weeks. Additionally, fish kept in white and black background tanks were then subjected to crowding stress. After 2, 9, 16 and 23 days, blood samples were taken and plasma cortisol, alpha melanocyte stimulating hormone (α-MSH) and glucose values were analysed and compared with values from uncrowded fish from white or black tanks. Measurements of plasma cortisol and α-MSH in unstressed red porgy from white, grey and black tanks revealed no significant differences among the three groups. However, the results show that background colour markedly affects the in vitro interrenal sensitivity to both α-MSH and ACTH, as interrenal cells from black adapted fish had become virtually unresponsive to both secretagogues. Crowded fish on a black background showed a prominent increase in plasma cortisol after 2 days, which was followed by a recovery. In fish crowded on a white background however, the increase of cortisol was lower but was maintained through the entire experiment. Plasma α-MSH levels increased at 23 days as a consequence of crowding; this increase was also dependent on the background, being more prominent in fish placed in white background tanks. Thus, in the red porgy, a white background appears to modify the stress response, particularly in the long term.

Non-invasive measurement of steroids in fish-holding water: important considerations when applying the procedure to behaviour studies

Fish behaviourists are increasingly turning to non-invasive measurement of steroid hormones in holding water, as opposed to blood plasma. When some of us met at a workshop in Faro, Portugal, in September, 2007, we realised that there were still many issues concerning the application of this procedure that needed resolution, including: Why do we measure release rates rather than just concentrations of steroids in the water? How does one interpret steroid release rates when dealing with fish of different sizes? What are the merits of measuring conjugated as well as free steroids in water? In the ‘static’ sampling procedure, where fish are placed in a separate container for a short period of time, does this affect steroid release—and, if so, how can it be minimised? After exposing a fish to a behavioural stimulus, when is the optimal time to sample? What is the minimum amount of validation when applying the procedure to a new species? The purpose of this review is to attempt to answer these questions and, in doing so, to emphasize that application of the non-invasive procedure requires more planning and validation than conventional plasma sampling. However, we consider that the rewards justify the extra effort.

Water cortisol is a reliable indicator of stress in European sea bass, Dicentrarchus labrax

[This study examined cortisol release into the water by European sea bass, Dicentrarchus labrax . The time-course of plasma and water cortisol concentrations were determined in adult fish subjected to acute stress, by sampling blood and water at 0 h (before stress) and 0.5, 1, 2, 4, 8 and 24 h after stress. Sea bass showed a typical stress response, with plasma glucose and lactate concentrations peaking at 2 h, and plasma cortisol levels peaking at 1 h. Cortisol release rate into the water increased in response to stress and was positively correlated with plasma cortisol concentrations. In a further trial, juvenile fish were confined at densities of 20 and 50 kg/m 3 and water cortisol was evaluated over a 24 h period. Cortisol release rates peaked between 0–1 h in the high and 1–2 h in the low density group. In conclusion, these results provide strong evidence that cortisol release rate into the water can be used as a non-invasive method for the assessment of the stress response and that although sea bass presents a high blood stress response after exposure to acute husbandry stressors, it is releasing less cortisol into the water compared to other species previously examined., This study examined cortisol release into the water by European sea bass, Dicentrarchus labrax . The time-course of plasma and water cortisol concentrations were determined in adult fish subjected to acute stress, by sampling blood and water at 0 h (before stress) and 0.5, 1, 2, 4, 8 and 24 h after stress. Sea bass showed a typical stress response, with plasma glucose and lactate concentrations peaking at 2 h, and plasma cortisol levels peaking at 1 h. Cortisol release rate into the water increased in response to stress and was positively correlated with plasma cortisol concentrations. In a further trial, juvenile fish were confined at densities of 20 and 50 kg/m 3 and water cortisol was evaluated over a 24 h period. Cortisol release rates peaked between 0–1 h in the high and 1–2 h in the low density group. In conclusion, these results provide strong evidence that cortisol release rate into the water can be used as a non-invasive method for the assessment of the stress response and that although sea bass presents a high blood stress response after exposure to acute husbandry stressors, it is releasing less cortisol into the water compared to other species previously examined.]

Physiological colour changes in the red porgy, Pagrus pagrus, following adaptation to blue lighting spectrum

The effect of lighting spectrum (full vs. blue) on skin colour and stress response in red porgy, Pagrus pagrus, held under a 12L:12D photoperiod was investigated. Fish exposed to blue lighting spectrum became gradually paler with a maximum lightness value (L = 45.33) on day 27, significantly higher than control fish (L = 31.49). However, there was no difference in skin melanin content, hue and chroma among the experimental groups. There was also no statistically significant effect of lighting spectrum on average glucose, thyroxine (T4), triiodothyronine (T3), cortisol (F) and Melanophore Stimulating Hormone (MSH) plasma concentrations nor in the pattern of changes during the time course of the experiment. Results showed that lighting spectrum affects skin lightness but not the chromaticity attributes hue and chroma. This effect is due to changes in the motility of the melanophores (the area occupied by melanosomes) and is not mediated by MSH or the general stress response.