Animal welfare in modern production systems for fish
Study 1. Why is the intestinal barrier function decreased by husbandry related stress?
The intestinal epithelium constitutes a selective barrier, facing the complex tasks of blocking pathogens and harmful substances while, simultaneously, allowing absorption of nutrient, ions and water (Fig. 1). An optimal function and regulation of the intestinal barrier is essential for maintenance of intestinal health and thus the health and welfare of the whole fish. We have shown that husbandry related stress weakens the intestinal barrier function which results in a leaky intestine. This is a serious threat to the health and welfare of the fish. However, the physiological mechanisms behind a leaky intestinal barrier are poorly understood. In a stressful situation the blood flow is redirected away from the gastrointestinal tract in order to increase the blood flow to the musculature as a part of the stress response. This will lead to a reduction in oxygen levels in the intestinal tissue which, in mammals, is well known to create damages to the tissue (ischemia). Damages may however also arise when the blood flow is restored (reperfusion). A major aim of this experiment is to investigate possible ischemia and reperfusion effects and damages also in the gastrointestinal tract of fish. By use of state-of-the-art surgery the blood flow to the rainbow trout intestine will be stopped (occluded) for a period of time. Tissue damages will be investigated using physiological in vitro techniques in combination with conventional histology and molecular techniques either directly after a period of ischemia or after ischemia followed by reperfusion.
Fig. 1. Intestinal barrier function of fish.