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

溶解有机物(DOM)是植物和土壤物质分解的产物，这些物质冲进水体并与水生生物本身产生的有机物质混合。在浓度较高的情况下，例如在排干森林地区的水域中，DOM会产生茶色的棕色。虽然通常被认为是生物惰性的，但最近的发现表明，DOM可能对水生动物有直接影响。目前的计划试图通过在三个不同但重叠的领域进行研究，加深对DOM的这些生物学作用的了解。*研究重点之一是确定氨基酸--DOM的一种简单形式--是否有助于鱼类早期生命阶段的生长。在幼鱼形成胃肠道吸收营养之前，有证据表明氨基酸被皮肤吸收并支持幼鱼的健康，但这一点尚未得到实验证明。这一假设将在目前的提案中得到检验，如果被证明是正确的，将提供一种提高水产养殖鱼类生产力和存活率的方法，并可能导致更便宜和更有效的鱼类饲料。这项研究还将通过研究鱼类肠道中消化和吸收过程的发展，有助于加强对鱼类营养的基本了解。*第二个研究重点提出了关于DOM在水生无脊椎动物(如昆虫幼虫)中的营养作用的类似问题。众所周知，富含DOM的水域比缺乏DOM的水域支持更多的昆虫幼虫，如黑蝇和蚊子的幼虫。有证据表明，这是因为这些幼虫和其他淡水无脊椎动物，如水蚤，可以使用DOM来帮助生长和生存。了解DOM在支持昆虫营养方面的作用，将有助于深入了解影响叮咬昆虫季节性变化的因素，这些昆虫是疾病和刺激的重要媒介。它还可能有助于预测改变水生DOM浓度和组成的因素(例如森林火灾、土地利用变化)将如何影响昆虫数量，这些因素反过来可能对人类健康和疾病产生影响。*最后的研究重点试图了解不同DOM的不同化学成分如何影响它们直接改变水生动物生物学的能力。这项工作建立在越来越多的人认识到DOM可以直接给动物造成压力的基础上。然而，为什么某些途径会受到影响，以及为什么这些影响仅限于某些DOM，还不是很清楚。鉴于大多数研究忽略了DOM对水生动物健康的可能作用，这项研究将提高人们对DOM对生物群作用的认识，并将代表着朝着能够基于特定地点的DOM组成预测这些影响的模型迈出的第一步。

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.