Evaluación de las condiciones de cultivo durante la cría de la acedía (dicologlosssa cuneata) y estudio integrado de su fisiología y comportamiento en cautividad

Resum

In recent years, aquaculture is gaining an increasing importance because natural populations of commercial species are being strongly threatened by uncontrolled fishing activity, marine pollution and other factors that could lead certain species to disappear. However, in Spain only seven species are grown on a commercial scale: sea bass, sea bream, turbot, red tuna, meagre, Senegalese sole and eel. Thus, it is necessary to diversify the species to be cultivated by the Spanish marine aquaculture, and the wedge sole ( Dicologlossa cuneata ) appears as a convenient candidate due to its high commercial value and its high growth rate and fertility. But for this, it is necessary to carry out a comprehensive research process to reach the effective zootechnical development of the species. In this context, the general aim of this PhD Thesis is to study and develop new knowledge on the culture of the wedge sole, based mainly on the physiological and behavioral responses to stress as related to the culture conditions. Thus, it is composed by different studies that on the one hand, try to evaluate the culture conditions during the breeding of the wedge sole, going deeply into the knowledge of two important parameters, the density and the feeding and its stress physiology and on the other hand, cover an integrated study of its physiology and behavior in captivity, because of its importance for culture optimization. Firstly, the effects of different densities were studied in diverse phases of the culture, concluding that the high cortisol values detected from the larval phase of D. cuneata seem to be related to the captivity conditions and that the high density of culture can be a stressor from 45 days after hatching (DAH). In addition, for this parameter cortisol was a good indicator of stress in short-term studies, but not for chronic stress situations. For this type of studies, muscle enzymes hexokinase (HK) and glutamate dehydrogenase (DH) were considered as good stress indicators. Plasma metabolites were not considered good markers in any of the cases. According to the daily rhythms of the species (food and locomotor), they were characterized by nocturnal activity. In spite of this and unlike to that observed in other flatfishes, D. cuneata showed some swimming activity during the day, seeming to be a behavior of the species and not derived from the captivity conditions. With regard to the feeding strategy, although the wedge sole was able to activate and use self- feeders, this type of strategy did not prove to be proper enough in terms of growth and welfare. By contrast, a nocturnal feeding schedule was associated with the higher levels of growth efficiency and the lower levels of stress; hence, it appears as the most appropriate feeding strategy for the wedge sole. Finally, based on the integrated responses (physiology and behavior), different coping styles with specific behavioral and physiological responses were identified: the CS1 group, defined as reactive fish, which take longer to recover the appetite in a new environment, with a fighting character against a stressor (exposure to air) and high levels of plasma cortisol after the stressor; and the CS2 group, defined as proactive fish, which recover faster the food intake, fight less in the net and have lower levels of plasma cortisol after exposure to the stressor. Furthermore, differences were detected between them in the levels of some enzymatic activities related to energy metabolism such as the glycogen phosphorylase (GPase), which acts on glycogenolysis. In conclusion, the studies that have been carried out throughout this PhD thesis have provided valuable information to improve the methodology of the wedge sole culture and animal welfare, which will have a positive impact on the aquaculture productivity and in the maintenance of species threatened by overfishing.