The mucosal surfaces and associated microbiota of fish are an important primary barrier and provide the first line of defense against potential pathogens. An understanding of the skin and gill microbial assemblages and the factors which drive their composition may provide useful insights into the broad dynamics of fish host–microbial relationships, and may reveal underlying changes in health status. This is particularly pertinent to cultivated systems whereby various stressors may led to conditions (like enteritis) which impinge on productivity. As an economically important species, we assessed whether the outer-surface bacterial communities reflect a change in gut health status of cultivated Yellowtail Kingfish (Seriola lalandi). Active bacterial assemblages were surveyed from RNA extracts from swabs of the skin and gills by constructing Illumina 16S rRNA gene amplicon libraries. Proteobacteria and Bacteroidetes were predominant in both the skin and gills, with enrichment of key β-proteobacteria in the gills (Nitrosomonadales and Ferrovales). Fish exhibiting early stage chronic lymphocytic enteritis comprised markedly different global bacterial assemblages compared to those deemed healthy and exhibiting late stages of the disease. This corresponded to an overall loss of diversity and enrichment of Proteobacteria and Actinobacteria, particularly in the gills. In contrast, bacterial assemblages of fish with late stage enteritis were generally similar to those of healthy individuals, though with some distinct taxa. In conclusion, gut health status is an important factor which defines the skin and gill bacterial assemblages of fish and likely reflects changes in immune states and barrier systems during the early onset of conditions like enteritis. This study represents the first to investigate the microbiota of the outer mucosal surfaces of fish in response to underlying chronic gut enteritis, revealing potential biomarkers for assessing fish health in commercial aquaculture systems.

No abstract

Solvent‐extracted soybean meal (SESBM) has been reported to cause subacute enteritis in certain fish species. Two 34‐day experiments investigated the effects of SESBM and soy protein concentrate (SPC) on the intestinal mucus layer and development of subacute enteritis in the hindgut of yellowtail kingfish (Seriola lalandi) at 22 and 18 °C. Fish were fed increasing levels of SESBM (Exp. 1: 0 g kg−1, 100 g kg−1, 200 g kg−1, 300 g kg−1) and SPC (Exp. 2: 0 g kg−1, 200 g kg−1, 300 g kg−1, 400 g kg−1). No visual signs of inflammation in the hindgut were observed in either experiment. However, increasing dietary SESBM significantly reduced mucus layer thickness. Neutral and acidic goblet cell mucin composition increased at 18 and 22 °C, respectively. A significant positive linear relationship was evident between goblet cell number and SESBM inclusion at 18 °C. SPC inclusion and water temperature had no significant effect on mucus layer thickness or mucin composition. However, at 18 °C, goblet cell numbers decreased with SPC inclusion. Results suggest the early stages of subacute enteritis may have been manifesting in SESBM fed fish. In the long term, mucus layer alterations associated with feeding SESBM may compromise fish health. Longer‐term studies should investigate the effects of feeding SESBM to yellowtail kingfish, particularly at suboptimal water temperatures.

No abstract

Temperate abalone species in aquaculture have a grow-out period of approximately 3 years because of their slow and heterogeneous growth rate. Abalone aquaculture is still a developing industry, and at least two major issues, nutrition and health, impede its development. Abalone are fed macroalgae on-farm in a number of countries, including China, Korea, South Africa and Chile. Formulated diets are crucial to the success of abalone aquaculture in countries where abalone do not grow readily when fed brown macroalgae or when access to macroalgae is insufficient for culture. Typically, the growth rate of abalone fed formulated diets is higher than abalone fed live macroalgae. However, due to a long production period, diets for abalone not only need to sustain high growth rates, but also maintain optimal health. Feeding live macroalgae improves the feeding activity, health and marketability of abalone. In this review, the nutritional requirements of abalone and dietary ingredients used in formulated diets will be discussed, together with the use of dried macroalgal meal as a dietary ingredient in formulated diets to improve the feeding activity, health and marketability of abalone in commercial production.