Using integrative acid-base physiology to improve the efficiency and sustainability of fish production

饲养和消化已经并将继续被广泛地用于基础和应用目的，在所有动物群体的一系列物种中。目前的提议代表了一个新的研究领域，为消化现象的研究提供了一个新的综合视角。它还为改善全球重要的鳟鱼和鲑鱼水产养殖中从食物到生长的转化提供了一种以前未曾预见的机制。商业应用的潜力已经与英国和全球最大的鳟鱼饲料生产商Skretting建立了工业合作伙伴关系。这个提议源于我们在2008年的最新发现，即与哺乳动物摄食有关的一种主要现象，即碱性潮，也发生在硬骨鱼（硬骨）身上，这在以前没有被记录下来。碱性潮是指在饭后数小时内血液中碳酸氢盐（一种碱）和pH值（即更碱性）升高，这是由于需要平衡胃酸的分泌。我们估计，这需要消耗鳟鱼消化一顿饭所需能量的5%到40%（取决于饲料的缓冲能力）。由此产生的血液酸碱紊乱也将导致一系列生理后果，包括对呼吸气体交换、盐和水平衡、能量使用的潜在负面影响，最终将限制食物转化效率和生长速度。鳟鱼对这种血液酸碱紊乱的一个关键反应是（通过鳃）将多余的碳酸氢盐碱排泄到外部水中，这是一个持续36小时的补偿过程。任何可能减轻碱性潮程度或缩短恢复时间的处理方法对水产养殖业来说都是极有价值的。这是因为这样的处理可以减少鱼类的能量消耗（促进更快的生长速度），降低养鱼户的经济成本，还可以减少对目前用于制作鱼粉（商业鳟鱼食品的主要成分）的日益昂贵和难以争夺的海洋资源的影响。该项目将侧重于碱性潮对虹鳟鱼的生理后果和成本，特别是这可能如何影响水产养殖条件下生长的生物和经济效率。通过了解碱性潮的生理影响，以及它们如何受到环境和饮食变量的影响，我们应该能够了解这在自然界中是如何变化的（渔业自然喂养的饲料具有非常不同的缓冲能力），以及如何最大限度地减少水产养殖中鱼类的能量成本。我们的目的是研究鱼类生活的淡水的温度和化学成分如何影响它们对碱性潮的反应和恢复时间。我们也会对饮食进行调整，看看能否减少鱼胃分泌酸的需求，减少碱性潮，从而节省能量，优化鱼的生长。我们将在埃克塞特的实验室条件下利用实验生理学研究这些现象，并在挪威斯塔万格的Skretting水产养殖研究中心在类似水产养殖的条件下进行商业规模的饲养试验，使用由Skretting水产养殖研究中心设计的新型饲料。

Feeding and digestion has been and continues to be extensively studied for both fundamental and applied purposes, in a range of species from all animal groups. The current proposal represents a novel area of research that offers a new integrative perspective on the otherwise well studied phenomenon of digestion. It also provides a previously unforeseen mechanism for improving the conversion of food-to-growth within the globally important aquaculture of trout and salmon. The potential for commercial application has generated an industrial partnership with Skretting, the largest trout feed producer in the UK and worldwide.The proposal stems from our recent discovery in 2008 that a major phenomenon associated with feeding in mammals, the alkaline tide, also occurs in teleost (bony) fish, in which it had not previously been documented. The alkaline tide is a rise in blood bicarbonate (a base) and pH (i.e. more alkaline) lasting several hours following a meal, which results from the need to balance the secretion of acid into the stomach. This carries an energetic cost that we estimate to be between about 5 and 40 % (depending on buffer capacity of the diet) of the energy used by trout to digest a meal. The resulting acid-base disturbance in the blood will also result in a host of physiological consequences including potentially negative effects on respiratory gas exchange, salt and water balance, energy use that will ultimately limit food conversion efficiency and growth rates. In trout one key response to this blood acid-base disturbance is to excrete the excess bicarbonate base into the external water (via the gills), a compensatory process that can last 36 hours. Any treatments that might either lessen the extent of the alkaline tide, or improve the recovery time, could be extremely valuable to the aquaculture industry. This is because such treatments would reduce the energetic costs for the fish (promoting faster growth rates), reduce the economic costs for the fish farmer, and also lessen the impact on increasingly expensive and hard-fought-for marine resources that are currently used to make fishmeal (the primary ingredient in commercial trout food).The project will focus upon the physiological consequences and costs of the alkaline tide in rainbow trout, and specifically how this might influence the biological and economic efficiency of growth in aquaculture conditions. By understanding the physiological implications of the alkaline tide, and how they are affected by environmental and dietary variables, we should be able to understand how this varies in nature (with fishing feeding naturally on diets with very different buffer capacity), and also how to minimise the energetic costs for fish within aquaculture. We aim to study how the temperature and chemistry of freshwater the fish live in can influence their response and recovery time for the alkaline tide. We will also manipulate the diet to see if we can minimise the need for the fish to secrete acid in its stomach and minimising the alkaline tide, thus saving energy and optimising fish growth.We will investigate these phenomena using experimental physiology under laboratory conditions at Exeter, as well as carrying out commercial-scale feeding trials at Skretting's under conditions similar to aquaculture, using novel feeds designed by Skretting's Aquaculture Research Centre in Stavanger, Norway.