Validation of Endoscopy for Determination of Maturity in Small Salmonids and Sex of Mature Individuals

—Fish maturity status, sex ratio, and age and size at first maturity are important parameters in population assessments and life history studies. In most empirical studies of these variables, fish are sacrificed and dissected to obtain data. However, maturity status and the sex of mature individuals can be determined by inserting an endoscope through a small incision in the body cavity wall and viewing the gonads. The objective of this study was to evaluate endoscopy in a field setting for gonadal assessment of streamresident forms of salmonids that mature at small sizes. Ninetyone brook trout Salvelinus fontinalis (60–210 mm fork length [FL]) were obtained via electrofishing and anesthetized. Maturity status and sex of mature individuals were determined with an endoscope. After recovery, individuals were euthanized with anesthetic and were dissected to validate the endoscopic classification. Endoscopy correctly determined the maturity status and sex of mature individuals for 96% of the brook trout; the highest accuracy was observed for the smallest (60–70 mm FL) and largest (.140 mm FL) individuals examined. In the misclassifications, visceral fat hampered visibility and was mistaken for mature testes. Immediate postprocedure mortality was 3.3% and was limited to individuals smaller than 70 mm FL. Endoscopy is a useful technique that can be used in field settings to assess maturity status and sex of mature fish with a low rate of immediate