The effect of fishmeal inclusion and prebiotic supplementation on the hindgut faecal microbiota of farmed Tasmanian Atlantic salmon (Salmo salar L.).

AIMS: Factors such as seasonal temperature and diet components, for example, fishmeal (FM) inclusion, can influence the composition of the gut microbiota of fish. In this study, we examined changes in the gut bacterial populations, in particular lactic acid bacteria (LAB), of farmed Tasmanian Atlantic salmon in response to different diets, during periods of higher water temperature. METHODS AND RESULTS: Between December 2011 and March 2012 hindgut faecal samples were collected from Atlantic salmon from a commercial fish farm in south of Hobart, Tasmania, fed with one of four trial diets containing either high or low FM inclusion levels with or without prebiotics. Overall there was little difference in the cultivatable bacterial populations in response to varying levels of FM and prebiotic supplementation, with LAB counts decreasing in response to increased water temperatures. However, it was observed that the high FM diet supported the presence of LAB in January, when these were not detected in the low FM diets. CONCLUSIONS: Our study indicates that the inclusion of higher amounts of FM rather than the addition of prebiotics has a greater effect on LAB colonization of the gut in Atlantic salmon. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the importance of the new fish feeds for promoting salmon health in aquaculture industry.

Dietary organic chromium supplementation and its effect on the immune response of rainbow trout (Oncorhynchus mykiss).

Recently, there has been an increasing interest in the potential effect of dietary chromium on the health of fish, particularly with respect to their metabolism and growth. Information as to the role of this mineral on their immune response, is limited however, so the aim of this study was to assess the effects of dietary chromium yeast supplementation on the immune response of rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout (56 g average weight) were fed three semipurified diets containing different levels of chromium (1540, 2340 and 4110 ppb), obtained by supplementing a basal diet with 800 or 2570 ppb chromium yeast, for 6 weeks. After this, time differences in their immune response were examined. A positive influence was observed on serum lysozyme activity at this time in fish maintained on the high chromium diet. The respiratory burst of head-kidney macrophages was also examined, and statistical differences were found in the level of respiratory burst elicited by macrophages from both groups of fish fed supplemented chromium after 3 and 6 weeks of feeding (absorbance at 3 weeks: 0.118, 0.166. 0.151 and 6 weeks 0.114, 0.168, 0.151 for the 1540, 2340 and 4110 ppb groups). Macrophages of fish receiving diets supplemented with chromium also had a greater ability to phagocytose yeast after 6 weeks than the control fish (40.5, 48 and 48.5% macrophages phagocytic in the 1540, 2340 and 4110 ppb groups, respectively). The results of the study show that chromium yeast is able to modulate the immune response of rainbow trout, and this effect appears to be both dose- and time-dependent.

Endocrine regulation of the phosphatidylinositol pathway in the Norway lobster, Nephrops norvegicus, and the shore crab, Carcinus maenas.

The present study examines the mode of action of eyestalk factors, in particular crustacean hyperglycaemic hormone (CHH), on known target tissues (muscle and hepatopancreas) in two decapod crustacean species, Nephrops norvegicus and Carcinus maenas. The possibility that receptors to CHH are coupled to an elevation of cytosolic Ca2+ derived from intracellular stores via activation of the phosphatidylinositol pathway was investigated. Using an inositol 1,4,5-trisphosphate (InsP3)-specific competitive binding assay, measurable levels of InsP3 were detected in hepatopancreas and muscle in both N. norvegicus and C. maenas. Incubation of these tissues in the presence of sinus gland extracts (two sinus gland equivalents) consistently increased InsP3. In addition, Carcinus CHH (10 nM) increased InsP3 levels in Carcinus hepatopancreas and muscle. Incubation of hepatopancreas from both species in 10 mM lithium saline increased basal levels of InsP3, suggesting a significant turnover of phosphoinositides in this tissue.