Effect of a functional feed additive on mitigation of experimentally induced gilthead sea bream Sparus aurata enteromyxosis.

In gilthead sea bream Sparus aurata, infection by Enteromyxum leei produces a cachectic syndrome with anorexia, weight loss, severe epaxial muscle atrophy and, eventually, death. Currently, there are neither vaccines nor effective prescription medicines to control this infection. Nutraceutical approaches are raising interest in the aquaculture industry, responding to the lack of therapeutic tools for the management of insidious chronic losses due to parasites. In this study, the effect of a commercially available health-promoting feed additive (SANACORE® GM) at 2 different doses was tested in comparison with a basal diet without the additive during a laboratory-controlled challenge with E. leei. Group performance and biometrical values were monitored, and an in-depth parasitological diagnosis, quantification of parasite loads and histopathological examination were carried out at the end of the trial. Supplemented diets mitigated the anorexia and growth arrestment observed in challenged fish fed the basal diet. This mitigation was maximum in the highest dose group, whose growth performance was not different from that of unchallenged controls. Treated groups also presented lower prevalence of infection and a lower parasite load, although the differences in the mean intensity of infection were not statistically significant. Although the decrease in parasite levels was similar with both doses of additive tested, the pathogeny of the infection was mostly suppressed with the higher dose, while only mitigated with the lower dose. The mechanisms involved in the effects obtained remain to be investigated, but the results point to a modulation of the immunopathological response to the infection.

Comparison of native, lyso and hydrogenated soybean phosphatidylcholine as phospholipid source in the diet of postlarval Penaeus japonicus bate.

Native and two modified forms of soybean phosphatidylcholine were used to study the nutritional effect of their fatty acids for postlarval Penaeus japonicus. Five semipurified and isolipidic diets were formulated using casein as a protein source. Three diets contained 1.5% of different types of phosphatidylcholine (95% purity), i.e. native soybean phosphatidylcholine, hydrogenated soybean phosphatidylcholine and 1-acyl lyso soybean phosphatidylcholine, besides 1% of n-3 highly unsaturated fatty acid formulated as triglycerides. Two negative control diets contained either triglycerides or ethyl esters as a source of n-3 highly unsaturated fatty acids without phospholipid. The experiment was conducted during two successive phases of 20 d starting from 12-d old postlarvae. Feeding the diet containing native soybean phosphatidylcholine resulted in significantly better growth and resistance to osmotic shock of P. japonicus postlarvae compared to the other diets. The total lipid content of the tissue was significantly increased by the supplementation of soybean phosphatidylcholine, whereas no significant difference was observed for the shrimp fed the modified phosphatidylcholine sources compared to the phosphatidylcholine-free diet at the end of the experiment. Shrimp fed the diet containing soybean phosphatidylcholine exhibited a higher polar lipid fraction in the whole body total lipid mainly as a result of the increased proportion of phosphatidylcholine and to a lesser extent of phosphatidylinositol at the expense of free fatty acids, free sterols and sterol esters. The content of 20:5n-3, 22:6n-3 and total n-3 highly unsaturated fatty acids in the shrimp tissue were higher in shrimp fed the native soybean and hydrogenated soybean phosphatidylcholine diets compared to those fed the phosphatidylcholine-free and 1-acyl lyso soybean phosphatidylcholine-based diets. The fatty acid profile of tissue phosphatidylethanolamine was more influenced by the type of dietary phosphatidylcholine than that of tissue phosphatidylcholine. In the absence of phospholipids in the diet, triglyceride fish oil and a mixture of ethyl ester concentrate and coconut oil with similar n-3 highly unsaturated fatty acids content were equivalent sources of n-3 highly unsaturated fatty acids. The beneficial effects of dietary phospholipids may be due to a more efficient transport and utilization of dietary neutral lipids through a better lipid mobilization following absorption in the intestinal mucosa rather than due to a better emulsification of neutral lipid in the gut lumen. The functionality of phosphatidylcholine in the diet of postlarval P. japonicus requires the presence of unsaturated fatty acids and an intact fatty acid moiety.

A standard experimental diet for the study of fatty acid requirements of weaning and first ongrowing stages of the European sea bass Dicentrarchus labrax L.: comparison of extruded and extruded/coated diets.

The stability of the coated lipid fraction of a standard weaning diet was verified by comparing growth and fatty acid incorporation for European sea bass fed diets with an identical formulation but prepared either by extrusion/coating or extrusion only. For each type of experimental diet, a (n-3) HUFA level of 1 and 2.5% of the dry diet was evaluated. European sea bass Dicentrarchus labrax L. were weaned and consequently reared for 23 days on the experimental diets in a recirculation system. A commercial weaning diet served as a control. Final individual dry weight of sea bass larvae weaned and ongrown for a total period of 30 days on the various diets did not differ significantly. The (n-3) HUFA content of the fish tissue was a reflection of the dietary (n-3) HUFA requirements of European sea bass during and immediately after weaning did not exceed 1% of the dry diet. The combined technique of cooking-extrusion of a basal diet followed by coating of a lipid emulsion proved to be a valid technique to prepare diets for studying quantitative fatty acid requirements of weaning and first ongrowing stages of marine fish. A standard diet with open formulation is proposed.