DETERMINATION OF SEX AND MATURATIONAL STATUS OF STRIPED BASS (MORONE-SAXATILIS) USING ULTRASONIC-IMAGING

Ultrasound images of the gonads of adult striped bass (Morone saxatilis) were recorded monthly to determine their efficacy in sexing and evaluating maturation status of broodstock throughout the year. The sex of adult (age V) broodfish was readily distinguished (95% accuracy) throughout the annual reproductive cycle. Adult (age II) female hybrid striped bass (M. saxatilis X M. chrysops) also were accurately (100%) sexed, whereas juvenile (age 1+) and adult (age II) male hybrids could not be accurately (42 and 45%, respectively) sexed with ultrasound. The maturational status of adult (age V) fish was readily differentiated throughout the annual cycle from cross-sectional measurements of gonad diameters on ultrasound scans. Maximum monthly ovary diameter ranged from a 11.4 mm in September to 26.3 mm at ovulation in March. Maximum monthly tests diameter ranged from 4.6 mm in July to 25.5 mm in March. Spermiating males exhibited larger mean (maximum) testicular diameters (23.5 mm) than non-spermiating males (13.1 mm). Maximum ovarian diameter was highly correlated (r = 0.92) with oocyte diameter. Maximum gonad size, determined from scans of the entire gonad, proved to be a more consistent index of maturity than average gonad size. Ripe female and spermiating male striped bass can be characterized as having maximum ovarian and testicular diameters of > 30 and 20 mm, respectively, although fish with smaller gonads may be capable of spawning. Ultrasound is a simple, effective, and non-invasive method to sex and assess maturational status of adult striped bass and perhaps other commercially and ecologically valuable (endangered) species.