Cellular epithelial barriers have important functions in the organisation of life. They are gate keepers that regulate the interaction of an organism with its surrounding environment. The intestinal epithelia is an example of an environment-organism barrier that regulates uptake from food; it transports nutrients from the intestinal lumen into the blood; at the same time it provides protection from environmental toxicants and pathogens. Another important function is osmoregulation. Fish travelling from fresh- to sea-water, for example, would literally dehydrate if the intestinal epithelium would not regulate ion and water uptake. Thus, mechanistic knowledge of the functions of epithelial barriers, such as the fish intestinal epithelium, is fundamental to our understanding of animal physiology, ecology and toxicology. This project aims to shed light on the role and functioning of the fish intestine as an environment-organism barrier. Little basic knowledge on fish intestinal epithelial function exists thus far because access to this tissue is difficult and the development of suitable models has been limited to short-lived ex vivo gut sac preparations. Therefore, we will address our aim by (1) engineering a piscine intestinal microenvironment based on newly available in vitro cell cultures and (2) visualizing and quantifying the physiologic and toxicologic response of this microenvironment to selected stimuli either non-invasive, on-line, or based on endpoint measurements, to observe intestinal barrier function. On-chip microfluidic design will be used because it enables to mimic the interaction of a model digestive fluid at the fluid-epithelia cell interphase, as well as communication between different intestinal cell types, by providing defined laminar flow and allowing for realistic, biologically relevant exposure and transport phenomena. The specific questions that we will address are: 1. How can the microchip be best designed to reconstitute the environment-intestinal barrier and allow sensible evaluation of cell function? 2. What is the longevity and differentiation state of the intestinal barrier cells if grown on the cell-chip and continuously fed a liquid mimicking the intestinal microenvironment? 3. How does the intestinal microenvironment respond to external stimuli, specifically: (a) What are the physiological changes induced by seawater adaptation? (b) Are intestinal cells capable to detoxify a model environmental contaminant by biotransformation and/or active transport? The focus will be on the teleost fish, rainbow trout (Oncorhynchus mykiss), which is well recognized as model species for freshwater fish in the Northern Hemisphere. Indeed, rainbow trout is of interest and widespread use in science (fish physiology, pathology and ecology), regulation of chemicals (ecotoxicology) and commerce (aquaculture, sports fishing). (...)