Rapid Estimation of Gonad-to-Body Ratio in Eastern Oysters by Image Analysis

The goal of this study was to develop a rapid and reliable method of quantifying the gonadal condition of eastern oysters Crassostrea virginica based on a gonad-to-body ratio (GBR). The objectives were to compare a previously established transect method with three alternative computer-based image analysis (IA) methods based on acquisition time, composite GBR values, and GBR values at different stages of gonadal development. The first IA method calculated the area of the gonad and body while eliminating the dorsal and ventral curvature of the gonad, the second calculated the area of the gonad and body while eliminating the gill area, and the third calculated the total area of the gonad and body. The GBR values from the first and third IA methods were not different from those from the transect method. The second IA method resulted in higher GBR values in 80% of the measurements compared with the other three methods. However, measuring the gonadal area and total body area was five times faster than with the transect method and, excluding the curvature, was nine times faster but susceptible to visual error. Based on the speed and comparability with the transect method, the third IA method was the most useful for quantifying gonadal development.