22 DECEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG mostly fungus protein indicated that the fungus-protein diet and the fishmeal-protein diet resulted in improved physiological responses compared to fish fed the commercial diet. With the aid of metabolomics approaches, the study authors were able to highlight the possibility of using alternative protein sources that may prove to be more sustainable for aquaculture in the future. Disease and Immunology Organisms grown in aquaculture settings are prone to diseases, usually caused by bacterial, viral or parasitic outbreaks, although the physical and chemical state of the aquatic environment can also have dramatic health effects. In some cases, mass mortalities as a result of severe disease epidemics have decimated certain sectors, leading to complete collapse with huge socioeconomic impacts. Physiological imbalances caused by genetic, nutritional or environmental factors can lead to suppression of immune function, which in turn can cause organisms to be more susceptible to pathogen exposure. Metabolomics can be used to evaluate health state, including effects of pathogen exposure, mechanisms of resistance and efficacy of disease treatments and management. Few studies have been conducted using metabolomics to assess health parameters in cultured marine invertebrates. Schock et al. (2013) used metabolomics to monitor health factors along the production line of Pacific white shrimp Litopenaeus vannamei from nursery to harvest in a superintensive aquaculture system. The findings highlighted a range of physiologically stressful conditions in nursery and raceway phases that could be improved to minimize health risk and improve production efficiency. Post-harvest Quality Control One of the biggest challenges for aquaculture is to achieve and maintain a high quality product from farm to market and into the hands of consumers. Product attributes such as nutritional value, meat quality, visual appearance, smell, firmness, juiciness, tenderness and flavor are subjective characters that influence physiological condition of mussel larvae was used to assess larval quality during hatchery production. Fast-growing and slow-growing larvae were separated and sampled over time. Metabolite profiles were obtained from these samples and the data were analyzed with a range of univariate and multivariate statistical methods to identify biomarkers for separation of the two larval groups. With this approach, metabolite–metabolite ratios involving levels of succinate, glycine, alanine, pyroglutamate and myristic acid were identified as biomarkers of mussel larval quality (Figs. 3 and 4). Based on the known functions of these metabolites, it was possible to identify potential biochemical pathways involved in larval performance. These pathways include energy metabolism, osmotic regulation, immune function and cell-cell communication. This study illustrates how metabolomics can be used to assess mollusc larval quality and signals the potential to generate predictive models of larval performance. It is envisaged that future research will eventually lead to easy-to-use tool kits to evaluate the physiological state of larvae throughout the rearing process. Nutrition and Diet Considerable research has been devoted to improve the nutritional content of feeds based on optimal requirements of specific cultured species. However, further studies are needed to develop sustainable and high-quality feed alternatives for individual performance improvement, disease prevention, enhancement of broodstock and gamete quality and mitigation of environmental impacts. Metabolomics is uniquely suited to assess metabolic responses to nutritional deficiencies or excesses and can be used to optimize feeding regimes for cultured species. There are a few metabolomics-based studies that have focused on positive and negative effects of food deprivation, interactions between diet, environment and diseases, and the effects of nutrient supplementation and substitution in a range of feeds. A study by Abro et al. (2014) tested the use of a protein-rich fungus Rhizopus oryzae as a substitute for fishmeal in Arctic charr Salvelinus alpinus diets. Analysis of metabolite profiles from fish fed a commercial diet, a diet of mostly fishmeal protein and a diet of (JUMP TO PAGE 66) FIGURE 3. Multivariate classification and feature reduction of metabolite biomarkers for slow-growing and fast-growing mussel larvae. FIGURE 4. Combined heatmap and hierarchical cluster analysis of metabolite biomarkers showing clear separation between slow-growing and fast-growing mussel larvae.
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