Iteroparous Females Research Articles

Gametogenesis in north west Atlantic teleosts

Gametogenesis has been studied in oviparous teleosts including winter flounder (Pletironectes americanus), American plaice (Hip‐poglossoides platessoides), ’turbot’ (Reinbardtius bippoglossoides), capelin (Mallotus villosus), Atlantic salmon (Salmo salar), char (Salvelinus alpinus), and Atlantic cod (Gadus morbua). In the cold environment of the north west Atlantic prolonged gametogenesis may occur with variations in the rates of change and lengths of maintenance for different phases of the cycles. Staggered promotion can occur so that some fish have periods of short or prolonged asynchrony even when they eventually fit classical descriptions of synchronous gametogenesis. For winter flounder oo‐genesis fits expectations of a minimum three years overall with promotion into vitellogenesis 10–11 months before spawning, but for other species a shorter vitellogenic phase may occur. Fall‐spawning salmonids may initiate gametogenesis much earlier than some reports previously suggested, and are asynchronous until close to spawning. Female winter flounder, salmonids and capelin spawn in a short burst whereas American plaice and Atlantic cod are batch spawners, as is Reinhardtius (contrary to a previous report). All the species studied have iteroparous females but capelin males are essentially semelparous; however iteroparous species have individuals which may not spawn every year.

Reproductive Conditions of the Atlantic Sturgeon (Acipenser oxyrinchus) in the Hudson River

Ninety-four prespawning adult Atlantic sturgeon (Acipenser oxyrinchus) were sampled in the Hudson River for age, sex, body size, gonad weight, fecundity, mature oocyte size, and plasma concentrations of gonadotropins, sex steroids, and vitellogenin during the spring spawning migrations in 1992 and 1993. In males, the age and total length ranged from 12 yr to 19 yr and from 133 cm to 204 cm and in females from 14 yr to 36 yr and from 197 cm to 254 cm. The majority of males were 13–16 yr old, and females were 16–20 yr old. Some females had residual atretic ovarian bodies, presumably remaining from a previous spawning and indicating iteroparity. Pre-ovulatory condition was recognized by migration of the germinal vesicle or by germinal vesicle breakdown and by significantly elevated plasma gonadotropins, progesterone, and vitellogenin. All pre-ovulatory females were captured upriver from Hudson River kilometer 136. Individual fecundity ranged from 0.4 million to 2.0 million eggs and oocyte diameter from 2.4 mm to 2.9 mm, and both characters exhibited a significant (p<0.05) positive relationship with female body size. Iteroparous females, tentatively identified by the presence of atretic bodies remaining in the ovary from a previous spawning, had significantly (p<0.05) higher fecundity and produced larger eggs, compared with females spawning presumably for the first time.

POPULATION DYNAMICS, LIFE HISTORY, AND PRODUCTION OF CYATHURA CARINATA (KRØYER) (ISOPODA: ANTHURIDAE) IN THE MONDEGO ESTUARY, PORTUGAL

ABSTRACT Previous studies of the benthic community in the Mondego estuary revealed that Cyathura carinata has spatially and temporally stable populations, has significant biomass throughout the year, and is one of the most abundant species in the estuary. The present work was carried out to study its population dynamics and life cycle in relation to physicochemical factors, and to estimate its productivity within intertidal mud flats. Cyathura carinata was sampled every two weeks from November 1990 to December 1991. It exhibited a contagious spatial distribution within the eulittoral zone, and its abundance changed seasonally, decreasing gradually from midfall to late spring, and increasing again from early summer to the following fall. Abundance appeared to be inversely related to emersion periods, and positively correlated with salinity and nitrate concentrations, while higher temperature and sediment organic enrichment appeared to have a negative effect on the abundance of organisms. Nevertheless, the correlations between abundance and environmental factors could not be considered as defining cause-andeffect, since environmental factors were also intercorrelated. Protogynous hermaphroditism was hypothesized, with males being present from March to September. Sexual activity began in early spring and recruitment took place through the summer. Two cohorts were produced, one in June and a second in August. Fecundity was significantly correlated with female size. In addition, higher salinities and pH favored higher fecundity. Although seasonal variations in growth rates were observed, growth was continuous through the life of the animal. Growth rates practically ceased during the winter, increased gradually from late winter to a maximum between early summer and midfall, and decreased again until the following winter. Life span was roughly estimated at 18-22 months. Sexual differentiation was estimated to occur within a period of 49-54 days from birth, for females, and 146-208 days for males. Sexual maturation in females was estimated to occur in 240-357 days (8-12 months). Cyathura carinata is a semiannual species in the Mondego estuary, with iteroparous females and an univoltine life cycle. Growth production (P) and elimination production (E) were estimated as, respectively, 5.6-9.9 and 11.8-22.3 g·m―2· year―1 ash-free dry weight. P/B and E/B ratios were estimated, respectively, as 1.65-2.03 and 3.74-4.37. Despite several differences with regard to the reproductive period, all populations of C. carinata studied along the European coasts show univoltine life cycles. Due to stable populations and life cycle characteristics, this species appears ideal for comparative ecophysiological and ecotoxicological studies in European estuaries.