In Arizona, various nonnative trout have been stocked since the early 1900s, and trout angling remains an important component of the sportfishing industry. These nonnative rainbow trout may have contributed to the decline of Little Colorado spinedace. The overall purpose of the research was to define interactions so that impacts to both trout management and spinedace populations can be minimized. Our objectives covered 5 broad areas of potential interaction: habitat use, diet, predation, health, and distribution.