Effect of temperature and diet composition on residue depletion of oxytetracycline in cultured channel catfish

Oxytetracycline is an antibacterial agent widely used in fish farming. The normal method of administration of oxytetracycline to the fish is to mix the drug into the feed. As a consequence, the concentration of the drug in feed, together with the preparation and the composition of feed, can influence the disposition of the drug itself. An experimental study was carried out to evaluate the residue depletion of oxytetracycline from muscle tissue of channel catfish (Ictalurus punctatus) fed different medicated diets. Three hundred channel catfish were randomly divided into six tanks (50 fish per tank), maintained at water temperatures of 18 degrees C (three tanks) and 23 degrees C (three tanks). The animals were fed with three diets, differing in their energy content and composition, for the duration of the experiment oxytetracycline was added to the diets at a level of 7500 mg kg(-1) for 7 d. After cessation of the treatment, five fish from each tank were killed on days 1, 3, 8, 13, 18, 24, 30, 35 and 40. Oxytetracycline residues in muscle tissue were determined by high-performance liquid chromatography. The results indicate that the energy level and chemical composition of the medicated diets administered to channel catfish influence oxytetracycline disposition in fish, and that temperature is an important factor in conditioning the reported dietary effects. Therefore, formulation of specific diets to administer drugs to farmed fish could assure better bioavailability of the chemotherapeutant and shorter withdrawal times

Seasonal variations in fat content and fatty acid composition of male and female coregonid 'bondella' from Lake Maggiore and landlocked shad from Lake Come (Northern Italy)

The Lake Maggiore bondella Coregonus macrophthalmus use perivisceral adipose tissue for gonadal development (with particular evidence in females), and muscle far as an energy source. Females use mainly saturated fatty acids (SFA) for energy purposes, while males use monounsaturates (MUFA) also. During vitellogenesis, females can also mobilize fatty acid precursors of gonadal highly unsaturated fatty acids of the omega 3 family from muscle tissue, bur in both sexes specific retention of docosahexaenoic acid (DHA=22:6 omega 3) in muscle is evident. Landlocked shad, unlike several freshwater fishes, can utilize the liver as well as body cavity and muscle as a fat reserve depot. The perivisceral fat stored during the feeding period appears to be utilized mainly for winter energy maintenance requirements. Lipid reserves from liver and muscle are also mobilized to meet the requirements resulting from gonadal development. In particular, females seem to use liver reserves, especially 18:1 omega 9, more than males, to meet the demands of ovogenesis. In the muscle, SFA are used mainly for energy purposes. During gonadal development, specific muscular and hepatic omega 3 highly unsaturated fatty acids (omega 3 HUFA=20 : 5+22 : 5+22 : 6) and omega 6 HUFA (20 : 4+22 :4+22 : 5) retention is evident in both sexes, while fatty acid precursors of omega 3 and omega 6 HUFA are mobilized, especially from muscle tissue. (C) 1996 The Fisheries Society of the British Isle