No abstract

The dietary lysine requirement of juvenile gilthead seabream was determined by the growth response of duplicate groups of fish (3.5 g initial weight) fed on six isonitrogenous (427 g kg−1) and isolipidic (135 g kg−1) diets containing graded levels of crystalline l‐lysine HCl, with dietary lysine content ranging from 36.3 to 79.7 g kg−1 of protein. The final indispensable amino acid profile of the diets except for lysine was formulated so as to resemble that of wild seabream whole body. Except for the reduced growth performance of fish groups fed the lysine‐deficient diets no other deficiency signs were apparent. Survival observed throughout the feeding period of 6 weeks was excellent. Weight gain (in %), specific growth rate, feed efficiency and daily protein deposition (DPD) were significantly improved in response to the increasing levels of dietary lysine up to 52.7 g kg−1 of protein and remained nearly constant thereafter. Whole‐body protein content followed a similar pattern as growth parameters in relation to dietary lysine level. Non‐linear regression analysis of DPD against dietary lysine level using the four‐parameter saturation kinetic model indicated a lysine requirement of 50.4 g kg−1 of protein for this species to support growth.

The pharmacokinetics and tissue distribution of oxolinic acid following an intravascular administration (15 mg kg À1 fish) were determined in sea bass, Dicentrarchus labrax L. (110 g), at 13 8C and 22 8C water temperature. The kinetic profile of the drug was found to be temperature dependent, with increased temperature having a greater effect on distribution after equilibrium and the elimination phase than on the distribution process. The distibution half-life of oxolinic acid was 1.15 and 2.76 h at 22 8C and 13 8C respectively, whereas the elimination half-life of the drug was 55 h at 22 8C and 315 h at 13 8C. The values of the apparent volume of distribution (1.44 L kg À1 at 22 8C and 3.31 L kg À1 at 13 8C) and the volume of distribution at steady state (5.2 and 14.7 L kg À1 at the high and low temperature respectively) were considerably different between the two tested temperatures. The total body clearance of the antibiotic was found to be low (1.47 L kg À1 day À1 at 22 8C and 0.80 L kg À1 day À1 at 13 8C). Lower rates of elimination were found for the liver compared with muscle, the difference increasing with increasing temperature, while elimination rates from the serum were higher than those of other tissues, especially at the high temperature.

The development of a test diet supporting good fish growth to be used in gilthead seabream indispensable amino acid (IAA) requirement studies based on dose-response relationship was the objective of the present study. Four isonitrogenous diets, one serving as control (diet C) based on fish meal LT, and three others in which the fish meal component was reduced to 45% and the rest of the nitrogen was provided by mixtures of crystalline AA were formulated. Diet S resembled the whole body IAA profile of wild seabream. Diet D was made deficient in all IAA and a 10% excess of IAA compared with diet S was used in diet E. Triplicate groups of fish were fed the diets to satiation for 6 weeks. Growth parameters and nutrient utilization efficiencies among diets C and S were similar, while excessive supplementation of IAA negatively affected most of them, compared with the control. Whole body composition was differentiated in relation to the diet fed. No significant differences were observed among groups fed the control and diet S. As shown by the results, the presence of crystalline AA in diet S does not significantly affect growth, and could therefore serve as control diet in IAA requirement studies of gilthead seabream. KEY WORDS

Valencia letourneuxi is a critically endangered freshwater fish in urgent need of targeted conservation. Little information is however available on its life history and feeding ecology; therefore, food resource utilization by V. letourneuxi was studied in its most abundant known Greek population of Chiliadou stream. The diet of this population appears to be dominated by microcrustaceans, Dipteran larvae, Acari, and Mollusca. Its feeding is highly dependent on seasonal prey availability and diversity, with niche overlap being low only between winter and the rest of the seasons, indicating that only during winter its diet differs significantly in relation to the other seasons. There are no significant sex-and sizerelated dietary shifts. This V. letourneuxi population is characterized by a generalist feeding strategy and appears to consist mostly of individuals with broad niches. Its generalist feeding pattern and dietary flexibility permits it to fully exploit this very diverse and rich habitat and may account for the high local abundance of this population.