Pre- and post-maturation survival in adults of the damselfly Pyrrhosoma nymphula (Zygoptera: Coenagrionidae)

The technique of mark-release-recapture was used to study survival before and after sexual maturity in adults of the damselfly Pyrrhosoma nymphula (Sulzer). Fewer females were recaptured upon return to water to breed despite no differences in dispersal or daily survival rate between the sexes over the immature period. Because females took longer to mature than males, their poorer recapture rate was attributed to greater overall mortality during their longer maturation phase. Survivorship curves for tenerals marked at emergence suggested that overall survival of immature adults was similar to, if not better than, that of mature adults. The reasons for this are discussed.
Jolly's model was used to estimate daily survival rates for mature adults. The assumptions of the model were tested rigorously. Estimates for females were statistically less reliable than those for males. Mean reproductive spans for males and females were 6.8 and 6.6 days, respectively, giving mean total adult lifespans of 19.4 days and 21.6 days for individuals surviving the maturation period.
Because neither sex visited the breeding site every day, sampling exclusively at water resulted in underestimation of mean reproductive spans for both sexes. Female reproductive spans were underestimated to a greater extent; because females remain away from water longer between visits, there is a greater chance that they will die before being recaptured.
Mean reproductive spans were also underestimated when only a sub-section of the habitat was sampled. Females were significantly more mobile than males and this increased the likelihood that they would move out of the study area, resulting in more severe underestimation. The importance of obtaining accurate estimates of mature lifespan for females is discussed.     

Reproduction of the Arctic copepodCalanus hyperboreus in the Greenland Sea-field and laboratory observations

The seasonal vertical migration of adultCalanus hyperboreus Krøyer and their female reproductive biology have been studied in the central Greenland Sea, based on 7-month coverage during one annual cycle. Females dwelled in surface waters only between April and July. Gonad maturation began after the summer descent into deeper waters between September and October in the absence of food. Breeding was assessed from gonad development and egg production experiments. It started around the beginning of November and was mostly completed by March/April, before the spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shallower depths. Males were mostly found during the breeding period, where they inhabited the 500- to 1000-m layer. Female dry weight was highest in August and November and lowest in February. Field observations were supplemented by observations on gonad development and egg production of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fecundity were determined at 0°C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fatter and produced up to 1000 eggs in several clutches deposited at regular intervals.     

Reproductive biology and implications for management of the spangled emperor Lethrinus nebulosus in the southern Arabian Gulf

The reproductive biology of the spangled emperor Lethrinus nebulosus in the southern Arabian Gulf was determined from the examination of 781 individuals collected between September 2008 and August 2009. There was no histological evidence of adult sex change, and sex ratios did not differ significantly from unity across all size and age classes. Testes had an ovarian structure and a remnant lumen which was not used for sperm transport; furthermore, residual oocytes were observed in the testes of some immature, resting and developing males. A dramatic change in the sex ratio of the smallest and youngest size and age classes suggested that juvenile female to male sex change occurred between 21·0 cm fork length (L(F)) and 24·0 cm L(F) at 1 year of age. The combination of histological evidence with the sexual composition of the size and age structures suggests a non-functional protogynous hermaphroditic sexual pattern, which is analogous to functional gonochorism. The spawning season was well defined, occurring once a year during March, April and early May. Peaks in spawning occurred after full moons, there was a cessation in spawning activity after new moons and spawning was completed within three lunar cycles. The distribution of males over the entire size and age ranges and the absence of inactive mature females during the spawning season suggested that the population was not constrained by sperm limitation. Size-specific and age-specific reproductive potential indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of L. nebulosus. The maximum recorded age (11 years), small mean size and young age at sexual maturation (L(m50) = 26·7 cm L(F), 2·1 years, for females and 19·4 cm L(F), 0·5 years, for males) may be a direct result of intensive demersal fishing in the southern Arabian Gulf.     

Reproductive biology of alfonsino Beryx splendens

The main aim of this work is to provide a detailed analysis of the reproductive cycle of Beryx splendens in the Juan Fernández Archipelago. The gonadosomatic index (I(G) ) and maturity ogives in both sexes were estimated using an extensive database collected by onboard scientific observers between January 2006 and October 2009. A histological analysis of maturation was also completed for females collected between May and December 2001. Variations in both I(G) and proportion of mature individuals were observed in fish with a fork length (L(F) ) >37 cm for females and >33 cm for males. The main reproductive season was in the austral winter and spring (June to November). Fork length at 50% maturity (L(50) ) was estimated as 39·67 cm for females (95% c.i. =39·34, 40·02 cm) and 36·88 cm for males (95% c.i. =36·45, 37·36 cm) using macroscopic analysis of gonads. Estimates for females using histological data varied slightly with an estimated L(50) of 43·67 cm (95% c.i. =42·82, 44·91 cm). Changes in I(G) and maturity were modelled as a function of month and L(F) within a generalized additive model framework. A high porportion of immature individuals were found throughout the year. The results of this study are compared with reproductive traits reported for B. splendens in other areas of its distribution and are discussed with reference to exploitation, vulnerability and conservation of the B. splendens stock in Juan Fernández Archipelago.     

Reproductive biology and implications for management of the painted sweetlips Diagramma pictum in the southern Arabian Gulf

The reproductive biology of the painted sweetlips Diagramma pictum was determined from 487 individuals collected between January and December 2010 in the southern Arabian Gulf. There was no evidence of sex change and the combination of histological results with the sex composition of the size and age structures indicated a gonochoristic sexual pattern. There were peaks in gonado-somatic indices for females in March and October with spawning occurring during two seasons (April to May and November). The mean size and age at sexual maturity (L(m50) and A(m50) ) were 35·7 cm fork length (L(F) ) and 2·9 years for females and 26·7 cm L(F) and 0·5 years for males. The maximum recorded age (11 years) and small mean size and young age at sexual maturity for males may be a direct result of intensive demersal fishing in the southern Arabian Gulf. There was an exponential increase in the cumulative reproductive potential with size and a linear increase with age for both sexes. The mean L(F) (L(c50) ) at which D. pictum became vulnerable to capture was 33·3 cm, which corresponded to only 3 and 7% of the cumulative reproductive potential of males and females, respectively. Size-specific and age-specific reproductive potential indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of D. pictum.     

Reproductive variables of Urotrygon rogersi (Batoidea: Urotrygonidae): a species with a triannual reproductive cycle in the eastern tropical Pacific Ocean

Reproductive aspects of the round ray Urotrygon rogersi were studied based on 2005 specimens obtained in the artisanal shrimp fishery operating on the Colombian Pacific coast. Females reached greater maximum total length (L(T) ), disc width (W(D) ) and mass (M) (38·0 cm, 19·9 cm and 348 g) than males (32·5 cm, 17·0 cm and 165 g). Sex ratio of juveniles and adults was 1:1. Clasper length increased rapidly between 10·0 and 12·5 cm W(D) . The smallest mature male measured 10·5 cm W(D) and the largest immature individual 13·7 cm W(D) . Male first maturity was reached at 61·8% of maximum W(D) , and estimated W(D50) was between 11·5 and 11·8 cm. The smallest mature female measured 10·5 cm W(D) ; the size at first maturity was 52·8% of maximum W(D) , and estimated W(D50) was between 11·8 and 12·3 cm. Embryos were found in females ≥ 10·5 cm W(D) and maximum fecundity was three embryos per female (mode = 1) and varied with maternal size. Embryos were found in all months, but three birthing peaks per year were identified and a gestation period of 4-5 months estimated. Based on ovulation time, embryonic growth and parturition dates, a triannual reproductive cycle was inferred for this species, with overlapping ovarian and uterine cycles. These results suggest that U. rogersi has a reproductive strategy based on low fecundity, a rapid reproductive cycle (short ovulation and gestation time), three birth peaks per year and large embryos. This strategy probably allows U. rogersi to withstand the fishing pressure they are subject to on the Colombian Pacific coast. The results also suggest that the study area is an important nursery and reproductive area for this species.     

Age and reproductive investment in grass goby females in the Venice lagoon

The present work describes the relationship between age and reproductive investment in the grass goby females in the Venice Lagoon. Age was estimated by otoliths reading, while reproductive investment was assessed by either the relative number of mature females across the breeding season and their gonadosomatic index. Females from different size/age classes differed in the timing and level of reproductive investment. The oldest females (3+ years old) appeared earlier in the spawning habitat, investing more at the beginning of the breeding season. In turn a later arrival in the spawning habitats has been observed for younger females (0+) and smaller individuals of 1+ and 2+ age classes. Present results gave evidence of an earlier age/size at sexual maturity of the grass goby in the Venice Lagoon compared to previous information on the species from the same lagoon and from other Mediterranean areas. Results were discussed in the light of previous data on reproductive strategy of nesting males and of the relationship between fishing pressure and life history traits in the Venice lagoon.     

Evidence for reproductive philopatry in the bull shark Carcharhinus leucas

Reproductive philopatry in bull sharks Carcharhinus leucas was investigated by comparing mitochondrial (NADH dehydrogenase subunit 4, 797 base pairs and control region genes 837 base pairs) and nuclear (three microsatellite loci) DNA of juveniles sampled from 13 river systems across northern Australia. High mitochondrial and low microsatellite genetic diversity among juveniles sampled from different rivers (mitochondrial φ(ST) = 0·0767, P < 0·05; microsatellite F(ST) = -0·0022, P > 0·05) supported female reproductive philopatry. Genetic structure was not further influenced by geographic distance (P > 0·05) or long-shore barriers to movement (P > 0·05). Additionally, results suggest that C. leucas in northern Australia has a long-term effective population size of 11 000-13 000 females and has undergone population bottlenecks and expansions that coincide with the timing of the last ice-ages.     

Social influences on sexual maturation of female Saguinus oedipus oedipus

The hypothesis tested was that Saguinus oedipus oedipus females housed with adult males would mature, sexually, at an earlier age than females remaining in their natal family groups. Six females were housed with strange, unrelated males. Five females remained in their natal groups. Blood samples were taken twice weekly, and the plasma was assayed for progesterone. Sexual maturation was operationally defined as that age at which plasma progesterone levels became consistently detectable. Females housing with males did mature at an earlier age than females remaining in their natal groups. In addition, it was noted that the presence or absence of a healthy, reproductive mother in the natal group was not related to the daughter's maturation age. However, whether the natal group, as a whole, inhibited maturation of young females, or an unrelated male accelerated maturation, or both, remains unknown.     

Dynamic egg maturation strategies in an aphid parasitoid

Abstract.  Females of the parasitoid Aphelinus albipodus both lay more eggs on younger stages of their aphid host, Aphis glycines , and contain more mature eggs in their ovaries when held with these younger host stages. This suggests that egg maturation is more rapid in the presence of younger host stages. Three factors explaining the difference in the egg loads of A. albipodus females exposed to various host stages are examined. These are (i) the number of host-feeding meals; (ii) the number of eggs laid; and (iii) the host stage utilized. Together, these factors explain 69% of the variance in A. albipodus egg load. The number of host-feeding meals taken by females is a strong predictor of egg load. More host meals are taken on young hosts, suggesting that host feeding contributes to the trend of faster egg maturation in the presence of younger hosts. Host stage has a strong impact on egg load even when the effect of host feeding is accounted for. There is no evidence for an effect of the oviposition rate on egg load. The results indicate that egg maturation by A. albipodus is dynamic; females mature eggs faster when in the presence of preferred hosts. It is hypothesized that this allows A. albipodus females to more closely match their reproductive effort to reproductive opportunities.     

Disentangling reproductive biology of the Patagonian toothfish <Emphasis Type="Italic">Dissostichus eleginoides</Emphasis>: skipped vs obligatory annual spawning,foraging migration vs residential life style

Patagonian toothfish Dissostichus eleginoides Smitt 1898, is an important commercially targeted Notothenioid species in South-Atlantic waters. In this study we aimed to clarify several aspects of reproductive biology of Patagonian toothfish in the Falkland Islands waters. Histological examination of female gonads indicates that with the beginning of maturation females maintain at least two populations of oocytes, suggesting that toothfish requires up to two years for oocytes development. Females become mature at an average size of 79.1 cm indicating a decrease of first maturity size if toothfish females in the Falkland Island waters. The majority of females spawn at the size from 101 to 130 cm total length. Distribution of reproductive phases shows an increase of females at developing stage in December and March prior to the spawning peaks in May and August respectively. However, the majority of the toothfish population consist of non-spawning individuals remaining in regressing phase (55.8 to 85.6%) including the spawning period. The skip-spawning for toothfish has been defined as reabsorbing non-reproductive and resting types. The abbreviation of oocytes development in the gonads was observed from 1 to 22.1% of females which omitted the spawning season. Most likely females which remain in the spawning area have the opportunity to spawn more often, whereas females which undergo foraging migration toward Northern parts of the Falklands waters return to the spawning ground less often. Females remain Northern area longer to accumulate necessary amount of energy. This hypnotise is supported by the presence of females in immature, developing and regressing phase throughout surrounding Falkland Islands waters. Presence of post-spawning females in regressing stage throughout the Falklands waters suggest that toothfish may undertake irregular spawning/foraging migration when favourable for spawning condition occur.     

Reproductive strategies of Red-bellied Piranha (<Emphasis Type="Italic">Pygocentrus nattereri</Emphasis> Kner, 1858) in the white waters of the Mamirauá flooded forest,central Brazilian Amazon

Despite being an important member of neotropical fish assemblages, as well as a species with an unenviable reputation, little is known about the reproductive ecology of Red-bellied Piranha, Pygocentrus nattereri, in the wild. We tracked the reproductive activity of piranhas in the flooded forests of Mamirauá Reserve, Central Brazilian Amazon, for 2 years, in an investigation that included over 3,000 individual fish. Contrary to expectation piranhas had not one, but rather two annual reproductive seasons, tuned to water level fluctuation and the flooding pulse. Females were found to have up to 30,000 oocytes, little more than one third of which were mature and available for spawning in a single batch. Sexual maturation (of both males and females) occurred at around 160 mm. At this point sexually active individuals (of both sexes) became dark and lost most of their red coloration. Ontogenetic changes in habitat selection were strongly associated with the spawning behavior of mature adults. We also found that flooded marginal vegetation and marginal grasses inside lakes were the preferred spawning areas. In contrast, non-reproductive individuals were found in open water and under floating meadows.     

Mating and role of seminal receptacles in the reproductive biology of the spider crab Maja squinado (Decapoda, Majidae)

The reproductive biology of the spider crab Maja squinado was analyzed based on monthly samples from an 18-month study carried out in Galicia (NW Spain) and laboratory experiments holding primiparous and multiparous females in captivity with and without males. The seminal receptacles of adult females were analyzed and their relationship with the presence and developmental stage of the eggs and the gonad maturity stage was determined. Gonad maturation in primiparous females began one or two months after the pubertal moult. Females having gonads in an advanced stage of development made their appearance in December and the first spawning took place in mid-winter or early spring. The percentage of ovigerous females from March to September was ∼75%. As the incubation period progressed, the ovaries became mature again in order to carry out the next spawning. Under experimental conditions the breeding cycle started earlier in multiparous females, during their second yearly cycle, than in primiparous ones. After mating, female spider crabs store sperm in seminal receptacles and this sperm is used in the fertilization of eggs immediately prior to spawning. The analyses of seminal receptacles consisted of the estimation of fullness and the number of differentiated sperm masses. The number of masses ranged between 0 and 6 in field samples (median for females with stored sperm=1) and was positively correlated with fullness. Differences in colour and volume of individual masses showed that, at least in some cases, females carried out successive matings with long intervals in between. This storage mechanism allowed females to fertilize successive broods without remating (as was also shown under experimental conditions). Juvenile females from shallow waters did not have developed seminal receptacles which indicated that mating was not possible until the onset of maturity. Postpubertal females in shallow waters (August to October), including animals participating in aggregations, always showed empty receptacles. The seasonality of receptacle fullness showed that mating involved hard-shelled females and occurred in deep water during the autumn migration from juvenile habitats or in the wintering habitats, during the last stages of gonad maturation (November to February). After fertilization ovigerous females continued to store sperm, but the volume was lower than in non-ovigerous females. Mating may occur in ovigerous females, particularly in the final period of incubation, because in females with broods almost ready to hatch, both new and older sperm masses were seen in the receptacles (distinguished by colour and size). The fullness of the receptacles decreased both in ovigerous and non-ovigerous females in the final phase of the annual breeding cycle (August–October), however, some sperm was still available. In the laboratory, mating was observed, and no courtship nor postcopulatory guarding was recorded. The analysis of receptacles from laboratory experiments indicated that primiparous and multiparous females showed differences in the seasonality of mating in the first phase of the breeding cycle (September–January), related to differences in the timing of gonad maturation and hatching. Mating occurred in the final stages of gonad maturation, a short time before hatching, and matings were detected in ovigerous females. Multiple matings were also evident, to a greater extent than in the field, probably due to the higher availability of males. Females underwent over four successive spawnings in the laboratory without having to recopulate, and the incubation lasted on the average from 40 to 58 days (∼18 and 16°C respectively) and the mean duration between hatching and the next spawning was 3.4 days. It is estimated that most females carry out three successive spawnings during the annual cycle.     

Reproductive pattern of the freshwater prawn Pseudopalaemon bouvieri (Crustacea,Palaemonidae) from hypo-osmotic shallow lakes of Corrientes (Argentina)

Pseudopalaemon bouvieri undergoes complete abbreviated development. The reproductive cycle (proportion and size of the sexually mature population and juvenile recruitment), fecundity and egg size of this prawn were examined in three subtropical shallow lakes. The reproductive cycle was seasonal; gonadal maturation occurred during the winter, ovigerous females were abundant in the spring and breeding occurred at the end of spring. Females produced small numbers of eggs (9–55) of relatively large sizes (1.0–2.1 mm). The proportion of ovigerous females with respect to the total number of females, the fecundity and egg size differed among the lakes according to the trophic state of the environments. Pseudopalaemon bouvieri has a reproductive strategy similar to other Palaemonidae species that inhabit nutrient-poor inland waters.     

Delayed timing of breeding as a cost of reproduction

Timing of breeding is a trait with considerable individual variation, often closely linked to fitness because of seasonal declines in reproduction. The drivers of this variation have received much attention, but how reproductive costs may influence the timing of subsequent breeding has been largely unexplored. We examined a population of northern wheatears Oenanthe oenanthe to compare three groups of individuals that differed in their timing of breeding termination and reproductive effort to investigate how these factors may carry over to influence reproductive timing and reproductive output in the following season. Compared to females that bred successfully, females that put in less effort and terminated breeding early due to nest failure tended to arrive and breed earlier in year 2 (mean advancement = 2.2 and 3.3 d respectively). Females that spent potentially more effort and terminated breeding later due to production of a replacement clutch after nest failure, arrived later than other females in year 2. Reproductive output (number of fledglings) in year 2 differed between the three groups as a result of group‐level differences in the timing of breeding in combination with the general seasonal decline in reproductive output. Our study shows that the main cost of reproduction was apparent in the timing of arrival and breeding in this migratory species. Hence, reproductive costs can arise through altered timing of breeding since future reproductive success (including adult survival) is often dependent on the timing of breeding in seasonal systems.     

Variation with reproductive status of PGE₂receptor immunoreactivities in the Bostrichthys sinensis olfactory system

The role of PGE(2) as a putative sex pheromone in Chinese black sleeper Bostrichthys sinensis was investigated, using immunocytochemistry and how the immunoreactivities of the prostaglandin E(2) (PGE(2) ) receptor subtypes EP(1) , EP(2) , EP(3) and EP(4) varied with reproductive status in the olfactory system was determined. The results showed that PGE(2) receptors were present in the whole of the olfactory system of B. sinensis, and that the number of receptors was linked to the reproductive status of the fish. The densities of EP(1) immunoreactivity in the olfactory epithelium of mature fish were significantly (P < 0·01) higher than those in immature fish of both sexes, and the densities of EP(2) and EP(3) immunoreactivities in mature fish were higher (but not significantly) than those in immature fish of both sexes. In the olfactory nerve, the density of EP(2) immunoreactivity in mature fish was higher (but not significantly) than that in immature fish in both sexes. In the olfactory bulb, the densities of EP(1-4) immunoreactivities in mature females were significantly (P < 0·05 or <0·01) higher than those in immature females, and the density of EP(4) immunoreactivity in mature males was significantly (P < 0·01) higher than that in immature males. As far as is known, the present study is the first report of the immunoreactivities of PGE(2) receptor subtypes in the olfactory system of a teleost, and offers new findings regarding the role of PGE(2) as sex pheromone and hormone in the reproductive behaviour and pheromonal communication of B. sinensis.     

Long-term and transgenerational effects of cryopreservation on rabbit embryos

The short-term effects of cryopreservation and embryo transfer are well documented (reduced embryo viability, changes in pattern expression), but little is known about their long-term effects. We examined the possibility that embryo vitrification and transfer in rabbit could have an impact on the long-term reproductive physiology of the offspring and whether these phenotypes could be transferred to the progeny. Vitrified rabbit embryos were warmed and transferred to recipient females (F0). The offspring of the F0 generation were the F1 generation (cryopreserved animals). Females from F1 generation offspring were bred to F1 males to generate an F2 generation. In addition, two counterpart groups of noncryopreserved animals were bred and housed simultaneously to F1 and F2 generations (CF1 and CF2, respectively). The reproductive traits studied in all studied groups were litter size (LS), number born alive at birth (BA), and postnatal survival at Day 28 (number of weaned/number born alive expressed as percentage). The reproductive traits were analyzed using Bayesian methodology. Features of the estimated marginal posterior distributions of the differences between F1 and their counterparts (F1 − CF1) and between F2 and their counterparts (F2 − CF2) in reproductive characters found that vitrification and transfer procedures cause a consistent increase in LS and BA between F1 and CF1 females (more than 1.4 kits in LS and more than 1.3 BA) and also between F2 and CF2 females (0.96 kits in LS and 0.94 BA). We concluded that embryo cryopreservation and transfer procedures have long-term effects on derived female reproduction (F1 females) and transgenerational effects on female F1 offspring (F2 females).     

Reproductive biology of the predator Macrolophus caliginosus: Effect of age on sexual maturation and mating

Macrolophus caliginosus is a polyphagous mirid bug native to the Mediterranean area where it is widely used as a biological control agent, both in protected and open-field vegetable crops. Its reproductive biology remains largely unknown and a better understanding of it will improve mass rearing and release strategies. In the present work, we studied the development of reproductive organs in females and males and how age conditioned receptiveness to mating in both sexes.Females with mature eggs in their ovarioles appear 3–4 days after adult molt with a similar pattern of ovary maturation in virgin females as in females that were kept with males of the same age. Newly molted males were found to already have active sperm in their seminal vesicles but their accessory glands did not completely develop until 3 days later. Receptivity for copulation paralleled ovarian and accessory gland maturation.     

Demographic Strategy in a Brown Trout Population in Western Norway1

(1) The individuals in the densely populated stock of brown trout, Salmo trutta L., living in Lake Lane and Stranda River, are small, mature at an early age, and have a relatively short life span. Such a demographic strategy appears favourable for populations having a large, but physically unstable spawning and nursery area, intense competition for food, and little vertebrate predation except for human exploitation. (2) For females, the age of sexual maturation appears largely dependent on growth-rate, size, and survival-rate of the fish. Males do not appear to have the advantage of a corresponding large body size. They mature when smaller and at more varying ages than the females, although the two sexes have almost identical growth-rates. (3) Sexually mature fish have higher condition coefficients than immature ones, which is probably an adaptation to ensure gonadal development and enhance the prospect of reproductive success. (4) Mortality appears to be largely dependent on the age when the fish achieve sexual maturation. Most individuals seem to die after their first spawning season. Females show a delay of one year in their sexual maturation relative to males. This adaptation gives protection to the females.     

Reproductive biology of the smooth butterfly ray Gymnura micrura

This study provides the first detailed information on the reproductive biology of the smooth butterfly ray Gymnura micrura. A total of 905 individuals were sampled, 377 of which were used for the reproductive study. Juveniles accounted for 75% of the sample, but all life cycle stages were present in the study area. The disc width at which 50% were mature (W(D50) )was estimated at 269 and 405 mm for males and females, respectively. The W(D50V) (based on the onset of vitellogenesis) was estimated at 359 mm. Uterine fecundity (mean ±s.d. = 3·8 ± 1·3; range: 1-6) was positively correlated with female size. A 3564% gain in mean wet mass was observed from egg to full-term embryo in utero. Size at birth ranged from 135 to 175 mm W(D) (19·5 to 55·0 g), with a mean of 165·1 mm W(D) (43·3 g). The embryo sex ratio was not significantly different from 1:1. The ovaries of pregnant females were undergoing vitellogenesis during gestation, with females ready to ovulate soon after parturition. Gymnura micrura may have an asynchronous reproductive cycle, with females reproducing continuously throughout the year.