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

饲喂和消化已经并将继续在所有动物种类的一系列物种中进行广泛的基础和应用目的研究。目前的提案代表了一个新的研究领域，它为消化现象提供了一个新的综合视角，本来研究得很好的现象。它还提供了一个以前未曾预见的机制，以改善全球重要的鲑鱼和鲑鱼水产养殖中从食物到增长的转变。商业应用的潜力已经产生了与英国和世界上最大的鲑鱼饲料生产商Skretting的工业合作伙伴关系。我们最近在2008年发现，与哺乳动物摄食有关的一个主要现象-碱性潮汐-也出现在硬骨鱼中，这是以前没有记录的。碱性潮汐是指餐后几个小时血液中碳酸氢盐(碱基)和酸碱度(即更碱性)的上升，这是由于需要平衡胃酸分泌而产生的。这带来了能量成本，我们估计大约是鲑鱼消化一顿饭所用能量的5%到40%(取决于饮食的缓冲能力)。血液中由此产生的酸碱失衡还将导致一系列生理后果，包括对呼吸气体交换、盐和水平衡、能源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。鲑鱼对这种血液酸碱紊乱的一个关键反应是将多余的碳酸氢盐排泄到外部水中(通过鳃)，这是一个可以持续36小时的补偿过程。任何可能减轻碱潮程度或延长恢复时间的处理，对水产养殖业都可能是非常有价值的。这是因为这样的处理将降低鱼类的能量成本(促进更快的生长速度)，降低养鱼户的经济成本，也减少对目前用于制造鱼粉(商业鲑鱼食品的主要成分)的日益昂贵和激烈争夺的海洋资源的影响。该项目将重点研究彩虹鲑鱼碱性潮汐的生理后果和成本，特别是这可能如何影响在水产养殖条件下生长的生物和经济效益。通过了解碱性潮汐的生理影响，以及它们如何受到环境和饮食变量的影响，我们应该能够理解这种变化在自然界中是如何变化的(渔业自然地以缓冲能力非常不同的饲料为食)，以及如何将水产养殖中鱼类的能量成本降至最低。我们的目标是研究淡水的温度和化学成分如何影响它们对碱性潮汐的反应和恢复时间。我们还将控制饮食，看看是否可以最大限度地减少鱼类对胃部分泌酸的需求，并最大限度地减少碱性潮汐，从而节省能源和优化鱼类生长。我们将在埃克塞特的实验室条件下使用实验生理学来研究这些现象，并在Skretting‘s进行商业规模的饲养试验，条件类似于水产养殖，使用挪威斯塔万格的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.