Reproductive Biology and Protandrous Hermaphroditism in Acanthopagrus latus

Detailed macroscopic and histological studies of the gonads of a full size and age range of Acanthopagrus latus from each season in Shark Bay, Western Australia, demonstrate that this species is a protandrous hermaphrodite in this large subtropical embayment. Although our scheme for the changes that occur in the ovotestes of A. latus during life is not consistent with some of the conclusions drawn for this species elsewhere, it is similar to that of Pollock (1985 J. Fish. Biol. 26: 301–311) for the congeneric Acanthopagrus australis. The ovotestes of males develop from gonads which contain substantial amounts of both testicular and ovarian tissue. The testicular component of the ovotestes of all males regresses markedly after spawning. During the next spawning season, the ovotestes either become gonads in which the testicular zone again predominates and contains spermatids and spermatozoa (functional males), or gonads in which the ovarian zone now predominates and contains mature oocytes (functional females). Once a fish has become a functional female, it remains a female throughout the rest of its life. In Shark Bay, A. latustypically spawns on a limited number of occasions during a short period in late winter and early spring and has determinate fecundity. The mean potential annual fecundity was ca. 2000000. The total length of 245mm, at which, during the spawning period, 50% of A. latus become identifiable as males, is very similar to the current minimum legal length (MLL) of 250mm, which corresponds to an age of ca. 2.5 years less than that at which 50% of males become females. Thus, although the spawning potential ratio suggests that the present fishing pressure is sustainable, the current MLL should be reviewed if recreational fishing pressure continues to increase.     

Reproductive Biology of the Coral-reef Goby, Asterropteryx Semipunctata, in Kaneohe Bay, Hawaii

A population of the Hawaiian coral-reef goby, Asterropteryx semipunctata, was sampled over a 12-month period to determine basic demographics and reproductive parameters. The sexes did not differ in median length or weight, although the largest males were considerably longer and heavier than the largest females. Overall adult sex ratio was 1:1; monthly sex ratios did not differ from unity except in June, when there was a significant female bias. Minimum age at maturity (17.5–19mm SL) was estimated to be 4.5–5 months after hatching. Nearly all fish over 22mm SL were mature. Mature females were found in all months of the year, and females that showed evidence of recent or imminent spawning were collected in every month except December. Gonadal analyses indicated a peak in breeding during the summer (May–July) and minimal spawning during the winter (January–February). Between 20% and 30% of females showed evidence of having spawned within the 24-h period prior to collection; therefore, it was estimated that females spawned, on average, at least once every five days and perhaps as frequently as every three days. Mean batch fecundity was 708 eggs (± 418), and was not well predicted by standard length, body weight, or somatic condition. Relative batch fecundity (mean = 1.44 oocytes mg^–1 somatic wet weight) varied seasonally, with higher values in spring and summer (April–July) than in fall and winter (September–January). Reproductive parameters are compared and contrasted with those of other gobiid fishes to elucidate general differences between temperate and tropical species.     

Aspects of the reproductive biology of the bass, Dicentrarchus labrax L. II. Fecundity and pattern of oocyte development

The European bass, Dicentrarchus labrax L., in common with most temperate marine teleosts, exhibits a distinct seasonal reproductive cycle. Its reproductive strategy is characterized by a high absolute fecundity (2-25 × 10⁵), both absolute and relative fecundity increasing with size and age. The cyclic pattern of oocyte development has been determined by histology and from oocyte size frequency analysis. Results show that the bass exhibits group-synchronous oocyte development and is a 'fractional spawner', i.e. it spawns a number (3–4) of discrete clutches in quick succession, successive clutches containing fewer oocytes. All oocytes which are recruited into the secondary growth phase (> 110 μrn) are either spawned that season or become atretic, i.e. no secondary oocytes are held over for the subsequent reproductive season.     

Clutch production in the darter Etheostoma lynceum and its implications for life-history study

We tested two hypotheses that describe previously untested assumptions about the appropriate stage(s) for use in determining clutch sizes in darters. Three sequential stages of clutch/ovarian development are recognized: mature oocyte/ovary, ripening oocytc/ovary, and ripe oocyte/ovary. Mean ratios of clutch size to female length (relative clutch size, RCS) were significantly smaller and variances of RCS were significantly greater in ripe females when compared to mature and ripening females. Correlation coefficients for the relationship between clutch size and standard length (S.L.) were significantly greater for mature and ripening females than for ripe females. Mean clutch size, adjusted for the S.L. covariate, was significantly greater in mature and ripening females than in ripe females. Thus, we conclude that counts of eggs from ripe females yield fecundity estimates that are lower and more variable than estimates from counts of oocytes from mature and ripening females collected at the same time. Based on this conclusion, we discuss methods for developing fecundity estimates in darters. Our results may be broadly applicable to other taxa of fishes with group-synchronous ovum development.