How now brown chow? Investigating direct functional roles for dissolved organic matter in aquatic animal nutrition and health

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Dissolved organic matter (DOM) represents the product of decomposing plant and soil matter that washes into water bodies and mixes with organic material generated by aquatic organisms themselves. At high concentrations, such as in waters draining forested regions, DOM is responsible for a tea-like, brown colouration. While generally considered to be biologically inert, recent findings suggest that DOM could have direct effects on aquatic animals. The current program seeks to develop an advanced understanding of these biological roles of DOM, through research in three distinct, but overlapping, areas. ******One research focus is to determine whether amino acids, a simple form of DOM, contribute to the growth of early life-stages of fish. Before larval fish develop a gastrointestinal tract that allows for the absorption of nutrients, there is evidence suggesting that amino acids are taken up by the skin and support the health of larval fish, but this has yet to be experimentally shown. This hypothesis will be tested in the current proposal, and if proven to be true, will offer a way of increasing the productivity and survival of fish in aquaculture, and could result in cheaper and more effective fish feeds. This research will also contribute to an enhanced fundamental understanding of fish nutrition, by examining the development of digestive and absorptive processes in the fish gut.******A second research focus asks a similar question regarding the nutritive role of DOM in aquatic invertebrates, such as insect larvae. It is known that DOM-rich waters support larger populations of insect larvae, such as those of black flies and mosquitoes, than DOM-poor waters. There is some evidence to suggest that this is because these larvae, and other freshwater invertebrates such as the water flea, can use DOM to aid growth and survival. Knowledge of DOM roles in supporting insect nutrition will offer significant insight into factors that influence seasonal variation in biting insects, important vectors of disease and irritation. It may also facilitate prediction of how insect numbers will be impacted by factors that change aquatic DOM concentration and composition (e.g. forest fires, land-use changes), which may in turn have implications for human health and disease.******The final research focus seeks to understand how the differing chemical composition of different DOMs affect their capacity to directly alter the biology of aquatic animals. This work builds on growing recognition that DOM can directly cause stress in animals. However, why certain pathways are affected, and why these effects are restricted to certain DOMs, is not well understood. Given that most studies ignore the possible roles of DOM on aquatic animal health, this research will increase awareness of DOM actions on biota, and will represent the first steps towards a model that will allow prediction of these effects based on site-specific DOM composition.