Chasmodes bosquianus is a bottom-dwelling, blenniid fish. The males of this species utilize and defend enclosed nest sites during the breeding season. This species was selected as an appropriate subject for a study of habitat selection and shelter choice among hole-nesting animals. Two experimental pools were prepared containing different arrangements of two types of objects. These objects were enclosures and open shelters. The former were designed to represent an idealized shelter of the type used for nesting purposes in the field. The latter, which were arranged in rows, were vertical rectangles representing topographical irregularities of the bottom. Placement of the objects resulted in four general types of space in the experimental pools: that adjacent to open shelters, that within enclosures, open space, and that next to the walls of the pool. The blennies utilized the space next to open shelters significantly more and open space significantly less than would be expected on the basis of randomly-oriented movement. In addition, the fish followed routes that passed near the objects, as opposed to crossing open space, as they moved about in the pools. There was a tendency to use enclosures more than could be accounted for by an explanation based on random movement. When the four general regions were compared to one another with respect to use by the fish, somewhat similar results were seen. Space adjacent to open shelters was used significantly more than was open space. Edges were also more heavily utilized than was open space. During short-term (one hour) observations, the fish were found to approach the enclosure (E2) at the junction of two paths more frequently than they did the enclosure (E1) located on a single path. According to one measure, they demonstrated a greater interest in E2 also. However, an explanation for this greater interest based solely on the number of times that the fish approached E2 seems reasonable. During long-term (three-day) observations, the fish were found to utilize enclosures on various paths more than they did an enclosure in open space. No preference among the enclosures on paths of differing complexity was seen.