Maturation, spawning and fertility of hybrid striped bass (Morone chrysops x Morone saxatilis) exposed to 6- and 9-month photothermal cycles

This thesis is aimed at improving techniques for induced maturation and artificial fertilization of Morone. Chapter 1 is a study of hybrid bass (n = 73) exposed to 6- or 9-month photothermal cycles which were formed by excising summer or summer and fall photothermal conditions from an annual regime. Shortened cycles abbreviated the interval between spawning and recrudescence, and advanced maturation by five and four months, respectively. All females developed functionally mature oocytes and ovulated after hormone injection. Maximum testicular sizes were similar and occurred after similar periods (153-199 d). Milt was produced in most (> 90%) males. Some milt characteristics differed among males in the three cycles, but fertility was similar. Findings suggest that excised cycles can advance maturation in hybrid bass, permitting off-season spawning.

In Chapter 2, effects of stripping frequency (3 times in 7 days) on semen quality was determined by measuring concentration, motility, osmolality, pH and sugars of milt. Male and female effects on fertility variation were measured by crossing all males and females. Sperm concentration was estimated by spermatocrit, ultraviolet and fluorometric absorbance. Motility (58 sec) and milt pH (8.44) were lowest (p < 0.05) after the third stripping. Concentration (1.76 x 10⁹ cells mL⁻¹) and osmolality also decreased with stripping frequency, but inconsistently among males. Fertility was highest during the second stripping and was correlated with milt pH (r = 0.762). Fertility variation was caused by females (p = 0.001). Results provide the first characterization of Morone semen quality. They suggest that frequent stripping alters milt parameters, that females account for most fertility variation, and that sperm concentration can be estimated reliably by spermatocrit.