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

Ultrasound images of the gonads of adult striped bass (Morone saxatili s) were recorded monthly to determine their efficacy in sexing and eva luating maturation status of broodstock throughout the year. The sex o f adult (age V) broodfish was readily distinguished (95% accuracy) thr oughout the annual reproductive cycle. Adult (age II) female hybrid st riped bass (M. saxatilis X M. chrysops) also were accurately (100%) se xed, whereas juvenile (age 1+) and adult (age II) male hybrids could n ot 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 diameter s (23.5 mm) than non-spermiating males (13.1 mm). Maximum ovarian diam eter was highly correlated (r = 0.92) with oocyte diameter. Maximum go nad size, determined from scans of the entire gonad, proved to be a mo re consistent index of maturity than average gonad size. Ripe female a nd spermiating male striped bass can be characterized as having maximu m ovarian and testicular diameters of > 30 and 20 mm, respectively, al though fish with smaller gonads may be capable of spawning. Ultrasound is a simple, effective, and non-invasive method to sex and assess mat urational status of adult striped bass and perhaps other commercially and ecologically valuable (endangered) species.