Antarctic krill meal and oil are well known sustainable and functional ingredients in aquaculture feeds, rich in essential aminoacids, omega-3s, phospholipids, micronutrients, and antioxidants such as astaxanthin , shown to enhance growth, health, and fillet quality in different fish species. The present findings are part of a wider field trial with seabass aimed at evaluating possible biological performance benefits of partial fish meal replacement by krill meal while using isonitr ogenous and isocaloric diets in organic production of European seabass. A 12-week field trial, with juveniles weighing 4.5 grams, was carried out at Galaxidi Marine Farm in Greece under commercial organic fish farming conditions. Two identical and proximal sea cages were used , each housing approximately 170,000 fish. Performance data, including feed consumption, FCR and mortalities were recorded during the monitoring period and also at the end of the trial. When the final weights of fish reached approximately 60g, ten fish from each group were randomly selected , and sampled for liver and intestine histology. The histological status of the livers and the intestines were assessed using a qualitative scoring system. During the trial, an outbreak of vibriosis caused by Vibrio harveyi occurred affecting the section of the fish farm where the trial cages were situated, resulting in mortalities among the population, with no treatments administered. The control group fed fish meal-based diet exhibited clinical signs of severe enteritis, with intestines showing loss of normal tissue architecture, reduced villi length, pronounced reduction of supranuclear vacuoles, epithelial sloughing, and inflammation. In contrast, the intestines of the fish fed the krill including diet maintained normal tissue architecture, displaying a normal histological appearance with well-developed villi, particularly rich in supranuclear vacuoles, especially in the distal gut area.
Although no statistically significant differences in biological performance data recorded were observed between the groups, the histological observations indicate that incorporating krill meal into organic fish feeds has the ability to strengthen intestinal resilience in seabass and expedite the healing process of lesions associated with bacterial enteritis. These findings are in agreement with other published studies indicating the advantageous effects of krill meal enriched diets in wound healing and tissue restoration. Of particular note is the possibility of developing further the inclusion of krill meal in functional fish diets aimed at facilitating recovery post-bacterial enteritis infections under commercial farm conditions.