Metabolic basis of growth variation in juvenile sole (Solea senegalensis, Kaup 1858)

Dissertação mest., Aquacultura e Pescas, Universidade do Algarve, 2009The general aim of this study was to understand the underlying factors responsible for the individual variation in growth of juvenile Senegalese sole (Solea senegalensis). Senegalese sole is a species of high commercial value and high interest for aquaculture in Europe, therefore it would be important to understand these individual variations. Understanding the causes for individual variation in growth in relation with the feed intake, metabolic rate and response to stress contributes to maximize the production efficiency by reducing food waste and improving water quality. In order to identify the possible factors responsible for the individual variation in sole growth, its relationship with metabolic rate, stress response and feed intake was determined. Twelve fish with 18.49 ± 2.94g of initial weight were kept in standard conditions and feed once a day, during a period of six months. Individual oxygen consumption measurements in Sole juveniles were determined by flow-through respirometry at standard conditions, after the fish were fed a single meal and after a stressful condition. Blood samples for plasma cortisol, were taken from all fish at the start of the experiment (control, indicative of basal levels) and after stress exposure. Quantification of individual feed intake was performed by incorporation with radio-opaque ballotinis glass beads in a dry feed, followed by radiography to quantify the amount of ingested pellets. Individual fish exhibited pronounced variation in growth (final weight ranging from 30.45 to 67.53g), oxygen consumption of fasted fish (108.0 to 447.4 μmol/g/h), oxygen consumption of fed fish (174.7 μmol/g/h to 813.5 μmol/g/h), oxygen consumption after emersion stress (186.8 μmol/g/h to 376.7 μmol/g/h), and plasma cortisol after emersion stress (4.81 ng/ml to 46.45 ng/ml). Individual differences in metabolic rate do not contribute to explain individual differences in growth. However, after emersion stress individual differences in stress response seem to play a role in explaining individual differences in growth, what may result from different copying styles. Sole feed intake as measured by X-ray does not seem to be a good indicator of growth rate. The oxygen consumption increases both when fish are fed and after an emersion stress, as result of additive costs of growth and stress to the cost of maintenance. All together, this study suggests that individual variation of growth in Solea senegalensis is essentially due to genetic variation, and its reduction may accomplished when genetic selection programs are adopted. Furthermore, a study with a larger number of fish and over a larger time period would be important to check some of the trends found in this thesis between growth potential, metabolic rate and coping styles of Senegalese sole