Integrative physiology as a tool towards good animal welfare and sustainability in aquaculture: Focus on intestinal function and health

The human population is growing, and the world’s leaders are trying to provide humans with food resources and at the same time setting goals promoting sustainable food production. This means that we need to find new food sources that are not in conflict with future generations’ right to a world without hunger and environmental destruction. We need to move away from traditional linear economy take, make, consume, and dispose and work towards circular economy where waste becomes resources. Aquaculture is the fastest growing food production industry in the world. 70 % of the earth’s surface consist of oceans and only a fraction is used for marine aquaculture. Therefore, marine aquaculture has potential for increasing the world food production. However, aquaculture like all industrial food productions has an environmental footprint and animals produced for food consumption should be treated according to animal welfare guidelines. In the current thesis we use several integrative physiological measurements to work towards sustainable food production without compromising animal welfare. There are many ways to achieve sustainability in aquaculture and not all are within the scope of this thesis. One of the unsustainable targets is feed production and optimal nutrient uptake. Feed carries the largest environmental impact. If there is a gap between the amount of feed given to the fish and how much that is converted into growth it will be reflected in profitability. Protein is the most important macronutrient for fish growth and normal body function. Fishmeal is considered the golden standard in animal feed but has its limitations and cannot increase in the same pace as the growth of the aquaculture industry. Vegetable sources has largely replaced fishmeal, but they also have their down sides because of incorrect nutritional profile and content of fibers and anti-nutritional factors. This has promoted the search for alternative protein ingredients that have equal qualities to fishmeal. In paper I we examined the dietary replacement of fishmeal with a shrimp and herring protein recovered from industry side-stream waters in feed for Atlantic salmon. We found that these proteins can be used as alternative ingredients in fish feed without compromising fish welfare based on the biological assessment using several indicators of intestinal and physiological impairment. These new ingredients can therefore be a sustainable alternative protein in fish feed contribute to circular economy where a previously wasted product becomes a resource. In paper II we investigate the mechanisms driving the intestinal amino acid transport in salmonids. The information found can contribute with some important basic knowledge that can be used in fish nutrition. Another way to achieve sustainability on a local scale is to secure the local food production and increase the number of species cultured through so called diversification. In this thesis we explore the basic physiological functions in Atlantic wolffish (Anarhichas lupus) that has been proposed as a new species for Swedish aquaculture because it is a native species with good temperament and high-quality meat. In paper III we found that Atlantic wolffish is a stress-tolerant fish with little detrimental effect on several welfare indicators after an acute stress treatment in form of air exposure and chasing. This is probably an attribute to its calm and docile behavior. Paper IV investigated the basic intestinal characteristics and paper V investigated the digestive capacity and nutrient uptake in Atlantic wolffish fed either in the morning or evening. Our data on intestinal morphology and functions revealed that Atlantic wolffish has interesting features such as higher methionine transport and lower resistance and high digestive enzyme activity in the distal intestine. These are characteristics for a nutrient transporting epithelium normally found in the proximal region of fish. Further, there was a difference in digestive capacity between the different regions. The research also shows that the plasma concentration of nutrients differs between fish fed at different time points. This information can be used for further studies when optimizing the feeding regimes for Atlantic wolffish.