Integrated multi-trophic aquaculture (IMTA) is an exciting alternative approach to mono-culture aquaculture that reduces environmental impacts of commercial aquaculture systems by combining the cultivation of fed aquaculture species (finfish) with extractive aquaculture species (e.g., shellfish and seaweed). This increases the sustainability and profitability of finfish culture as the organic particulate wastes can be removed by the shellfish extractive component and dissolved inorganic nutrients are extracted by the seaweed component. Shellfish play a critical role in an IMTA system by extracting particulate bound organic nutrients; however they may also influence pathogen dynamics by serving as a reservoir or as a barrier for finfish pathogens, depending on pathogen physiologies. The sea louse, Lepeophtheirus salmonis, has recently made a spectacular comeback as a major parasitic pest of farmed Atlantic salmon (Salmo salar L.) in the Northeast of the United States. The re-emergence of this parasite is due to development of louse resistance to SLICE™, the drug of choice for treating L. salmonis infestations over the last decade. Incorporation of mussel crops on salmon farms may be an alternative method to reduce the infectious pressure of sea lice on farms if mussels can consume copepodids, the planktonic and infectious stage of sea lice. Our study demonstrated that mussels can remove copepodids from the water column. Individual mussels were exposed to copepodids (200 copepodids l −1) for 30-and 60-min durations. Copepodids were observed in the buccal cavity and in stomach contents. Molecular analyses confirmed the presence of copepodids in mussel stomach contents.

No abstract

Background Mucosal surfaces of fish provide cardinal defense against environmental pathogens and toxins, yet these external mucosae are also responsible for maintaining and regulating beneficial microbiota. To better our understanding of interactions between host, diet, and microbiota in finfish and how those interactions may vary across mucosal tissue, we used an integrative approach to characterize and compare immune biomarkers and microbiota across three mucosal tissues (skin, gill, and gut) in Atlantic salmon receiving a control diet or diets supplemented with mannan-oligosaccharides, coconut oil, or both. Dietary impacts on mucosal immunity were further evaluated by experimental ectoparasitic sea lice (Lepeophtheirus salmonis) challenge. Results Fish grew to a final size of 646.5 g ± 35.8 during the 12-week trial, with no dietary effects on growth or sea lice resistance. Bacterial richness differed among the three tissues with the highest richness detected in the gill, followed by skin, then gut, although dietary effects on richness were only detected within skin and gill. Shannon diversity was reduced in the gut compared to skin and gill but was not influenced by diet. Microbiota communities clustered separately by tissue, with dietary impacts on phylogenetic composition only detected in the skin, although skin and gill communities showed greater overlap compared to the gut according to overall composition, differential abundance, and covariance networks. Inferred metagenomic functions revealed preliminary evidence for tissue-specific host–microbiota coadaptation, as putative microbiota functions showed ties to the physiology of each tissue. Immune gene expression profiles displayed tissue-specific signatures, yet dietary effects were also detected within each tissue and peripheral blood leukocytes. Procrustes analysis comparing sample-matched multivariate variation in microbiota composition to that of immune expression profiles indicated a highly significant correlation between datasets. Conclusions Diets supplemented with functional ingredients, namely mannan-oligosaccharide, coconut oil, or a both, resulted in no difference in Atlantic salmon growth or resistance to sea lice infection. However, at the molecular level, functional ingredients caused physiologically relevant changes to mucosal microbiota and host immune expression. Putative tissue-specific metagenomic functions and the high correlation between expression profiles and microbiota composition suggest host and microbiota are interdependent and coadapted in a tissue-specific manner.

Integrated multi-trophic aquaculture (IMTA) is an alternative approach to mono-culture aquaculture that reduces environmental impacts of commercial aquaculture systems by combining the cultivation of fed species with extractive species. Shellfish play a critical role in IMTA systems by filter-feeding particulate-bound organic nutrients. They may also increase or decrease disease risk on farms by serving as reservoirs or barriers for important finfish pathogens such as infectious salmon anaemia virus (ISAV). This study aimed to optimize culture and molecular assays in shellfish tissues and to determine the fate of ISAV in mussels, Mytilus edulis. To determine detection limits, qRT-PCR and culture assays in both CHSE-and ASK cells were optimized in ISAV-inoculated mussel tissue homogenates. Both qRT-PCR and culture assays performed in ASK cells had comparable detection limits of 10 2.8 TCID 50 mL À1 . The ISAV RNA genome was consistently detected in digestive gland tissue of ISAVexposed mussels. Viable ISAV was not detected in mussel tissues by culture analysis in CHSE-and ASK cells. The fact that qRT-PCR analysis resulted in positive cycle threshold (CT) values that corresponded to the detectable range of ISAV in ASK culture assays suggests that little to no viable ISAV particles are present in the mussel tissues.