Physiological stress responses of European seabass Dicentrarchus labrax related to changing operations of floating net cages in intensive farming conditions at the Moroccan M'diq bay.

Abstract

The present study purposed to quantify and compare in-situ the primary and secondary physiological stress responses, related to the operation of floating net-cages changing, in both sub-adults (523 days post hatching) and adults (916 dph) European sea bass Dicentrarchus labrax, under intensive farming conditions in the Moroccan M'diq Bay. Levels of cortisol, glucose, total cholesterol, total protein and lactate, as well as the percentage of hematocrit were measured before and after stress. The results showed significantly elevated levels of cortisol and blood glucose in both age groups, while total cholesterol and protein levels were unaffected. In fact, blood lactate was significantly reduced in sub-adults, while in adults this parameter was not affected by the operation. However, the hematocrit percentages measured after the operation were significantly higher than those found before the operation in both groups of fish, which is linked to the increased rate of oxygen renewal by the new net cages and the lower water temperature inside the cages. With regard to the age-specific response during this essential operation - before and after the operation - plasma cortisol, blood glucose and lactate concentrations, as well as plasma total protein levels, were significantly higher in sub-adults than in adults. It is concluded that aquaculture practices such as changing the aquaculture net-cage could have repercussions in terms of the classic physiological responses to stress in D. labrax. This article is protected by copyright. All rights reserved.