Beverly J. Macewicz

A Standardized Terminology for Describing Reproductive Development in Fishes

Abstract As the number of fish reproduction studies has proliferated, so has the number of gonadal classification schemes and terms. This has made it difficult for both scientists and resource managers to communicate and for comparisons to be made among studies. We propose the adoption of a simple, universal terminology for the phases in the reproductive cycle, which can be applied to all male and female elasmobranch and teleost fishes. These phases were chosen because they define key milestones in the reproductive cycle; the phases include immature, developing, spawning capable, regressing, and regenerating. Although the temporal sequence of events during gamete development in each phase may vary among species, each phase has specific histological and physiological markers and is conceptually universal. The immature phase can occur only once. The developing phase signals entry into the gonadotropin-dependent stage of oogenesis and spermatogenesis and ultimately results in gonadal growth. The spawning capable phase includes (1) those fish with gamete development that is sufficiently advanced to allow for spawning within the current reproductive cycle and (2) batch-spawning females that show signs of previous spawns (i.e., postovulatory follicle complex) and that are also capable of additional spawns during the current cycle. Within the spawning capable phase, an actively spawning subphase is defined that corresponds to hydration and ovulation in females and spermiation in males. The regressing phase indicates completion of the reproductive cycle and, for many fish, completion of the spawning season. Fish in the regenerating phase are sexually mature but reproductively inactive. Species-specific histological criteria or classes can be incorporated within each of the universal phases, allowing for more specific divisions (subphases) while preserving the overall reproductive terminology for comparative purposes. This terminology can easily be modified for fishes with alternate reproductive strategies, such as hermaphrodites (addition of a transition phase) and livebearers (addition of a gestation phase).

Latitudinal variation in reproductive biology and growth of female Dover sole (Microstomus pacificus) in the North Pacific, with emphasis on the Gulf of Alaska stock

Abstract Dover sole ( Microstomus pacificus ) have a wide distribution throughout the North Pacific, ranging from southern Baja California (26°N) to the Gulf of Alaska (GOA, 59°N). Prior to this study, our understanding of Dover sole reproductive biology was limited to the stock off the US west coast. This study was initiated to determine the length and age at maturity for Dover sole in the GOA. We also compared the length at maturity and growth rate across latitudes to test the hypothesis that individuals near the northern extent of their range (GOA stock) mature at a larger size than individuals in the southern stock off California and Oregon. Female Dover sole (n=273) ranging in length from 198–663 mm were collected opportunistically around Kodiak Island, Alaska, (55–59°N) from February 2000 to October 2001, with sampling concentrated in the months February-April, June–July, and October–November. All ovaries were examined to determine the maturity stage using standard histological criteria. The spawning season of Dover sole in the GOA spanned at least 4 months, from February to May. Dover sole in the GOA matured at a larger size than those off California and Oregon, with an estimated length at 50% maturity (ML 50 ) of 439 mm. At the same fish length that nearly 100% of Dover sole from California and Oregon waters are mature, Dover sole in the GOA are just beginning to mature. The estimated age at 50% maturity (MA 50 ) for female Dover sole in the GOA was 6.7 years and was similar to the MA 50 for cohorts at more southern latitudes. We attribute the latitudinal variation in ML 50 , combined with the similar MA 50 across latitudes, to spatial differences in growth rates.