The intestine of fish is a multifunctional organ: lined by only a single layer of specialized epithelial cells, it has various physiological roles including nutrient absorption and ion regulation. It moreover comprises an important barrier for environmental toxicants, including metals. Thus far, knowledge of the fish intestine is limited largely to in vivo or ex vivo investigations. Recently, however, the first fish intestinal cell line, RTgutGC, was established, originating from a rainbow trout (Oncorhynchus mykiss). In order to exploit the opportunities arising from RTgutGC cells for exploring fish intestinal physiology and toxicology, we present here the establishment of cells on commercially available permeable membrane supports and evaluate its suitability as a model of polarized intestinal epithelia. Within 3 weeks of culture, RTgutGC cells show epithelial features by forming tight junctions and desmosomes between adjacent cells. Cells develop a transepithelial electrical resistance comparable to in vivo measured values, reflecting the leaky nature of the fish intestine. Immunocytochemistry reveals evidence of polarization, such as basolateral localization of Na⁺/K⁺-ATPase (NKA) and apical localization of the tight junction protein ZO-1. NKA mRNA abundance was induced as physiological response toward a saltwater buffer, mimicking the migration of rainbow trout from fresh to seawater. Permeation of fluorescent molecules proved the barrier function of the cells, with permeation coefficients being comparable to those reported in fish. Finally, we demonstrate that cells on permeable supports are more resistant to the toxicity elicited by silver ions than cells grown the conventional way, likely due to improved cellular silver excretion.