Use of portable ultrasonography to determine ovary size and fecundity non-lethally in northern pike (Esox lucius) and white sucker (Catostomus commersoni)

The objective of this study was to investigate the feasibility of using field-based portable ultrasonography to accurately estimate ovary weight, gonadosomatic index (GSI) and fecundity in large-bodied fish species. These reproductive endpoints were estimated using ultrasound on prespawning female northern pike (Esox lucius) and white sucker (Catostomus commersoni) and compared with actual measured values determined post mortem. Using five cross-sectional ultrasound images in pike, estimated ovary weight and fecundity, but not GSI, were significantly correlated with measured values. All endpoints were overestimated by 21 to 23% using ultrasound in pike. In a subsequent experiment using 20 cross-sectional ovary images, estimated ovary weight, GSI and fecundity were significantly correlated with measured values in white sucker. Although underestimated by 5 to 12% using 20 cross-sectional images, there were no statistical differences among estimated and measured mean ovary weight, GSI and fecundity in white sucker using this approach. Based on the variances for GSI estimations in both species, power analysis indicated that the ultrasound technique could detect a 25% change in GSI using sample sizes of <20 fish. This study illustrates the utility of portable ultrasonography as a promising non-lethal technique for assessing reproductive endpoints in the field.