Dietary b-glucan (MacroGard®) enhances survival of first feeding turbot (Scophthalmus maximus) larvae by altering immunity, metabolism and microbiota

Reflecting the natural biology of mass spawning fish aquaculture production of fish larvae is often hampered by high and unpredictable mortality rates. The present study aimed to enhance larval performance and immunity via the oral administration of an immunomodulator, β-glucan (MacroGard®) in turbot (Scophthalmus maximus). Rotifers (Brachionus plicatilis) were incubated with or without yeast β-1,3/1,6-glucan in form of MacroGard® at a concentration of 0.5 g/L. Rotifers were fed to first feeding turbot larvae once a day. From day 13 dph onwards all tanks were additionally fed untreated Artemia sp. nauplii (1 nauplius ml/L). Daily mortality was monitored and larvae were sampled at 11 and 24 dph for expression of 30 genes, microbiota analysis, trypsin activity and size measurements. Along with the feeding of β-glucan daily mortality was significantly reduced by ca. 15% and an alteration of the larval microbiota was observed. At 11 dph gene expression of trypsin and chymotrypsin was elevated in the MacroGard® fed fish, which resulted in heightened tryptic enzyme activity. No effect on genes encoding antioxidative proteins was observed, whilst the immune response was clearly modulated by β-glucan. At 11 dph complement component c3 was elevated whilst cytokines, antimicrobial peptides, toll like receptor 3 and heat shock protein 70 were not affected. At the later time point (24 dph) an anti-inflammatory effect in form of a down-regulation of hsp 70, tnf-α and il-1β was observed. We conclude that the administration of MacroGard® induced an immunomodulatory response and could be used as an effective measure to increase survival in rearing of turbot

EFFECTS OF DIFFERENT DIETS ON THE DIGESTIVE PHYSIOLOGY OF ADULT NORWAY LOBSTER NEPHROPS NORVEGICUS

Rearing Norway lobsters for restocking is a management option to compensate fishing overexploitation, but this requires, among other topics, developing specific pellet diets. The activity of digestive enzymes and the histological organization of the hepatopancreas were analyzed to assess the effectiveness of a pellet diet on digestive performance. Thirty animals were reared individually for 6 mo, fed with mussels and pellets or starved. Comparisons with wild lobsters were also conducted. Survival rate of lobsters fed with frozen mussels was the greatest. Trypsin and amylase activity in the hepatopancreas of the lobsters fed pellets was greater than that of other treatments. In contrast, pepsin activity in the gastric juice of starved animals was the greatest. Levels of alkaline proteases in the gastric fluid were greater in lobsters fed with mussels and the pellet diet in contrast to fasted animals. Amylase was greater in specimens fed frozen mussels. The greatest level of lipid accumulation observed in lobsters fed with the pellet diet indicated a physiological imbalance between the absorptive and transport capacity of the hepatopancreatic cells resulting from an excess of dietary lipids. These results might serve as a reference for future studies for formulating feeds specifically designed for Nephrops norvegicus