Full-term Embryos Research Articles

Biological observations and new maximum reported sizes for two threatened rays: ornate eagle ray Aetomylaeus vespertilio and mangrove whipray Urogymnus granulatus from the Gulf of Mannar, India

Abstract Record-sized specimens of the ornate eagle ray Aetomylaeus vespertilio and mangrove whipray Urogymnus granulatus were caught by single-day trawlers off Pamban Island in the Gulf of Mannar, Tamil Nadu, India during 2021 and 2022. All were landed at the Pamban Therkuvadi Fish Landing Centre (FLC). The largest ornate eagle ray was 384 cm disc width (DW) and weighed 530 kg, setting a new global record for the species, as the previous maximum size was reported to be 300 cm DW. This specimen was landed on 19 July 2021. Another large specimen of this species (360 cm DW and total weight of 453 kg) was caught and landed on 12 August 2022. The landed mangrove whipray was 153 cm DW and 150 kg total weight, larger than the previously reported maximum size of 141 cm DW. The morphometrics, stomach contents and reproductive state were studied. One of the eagle rays was a pregnant female with three full-term embryos in the uterus, while the whipray was a spent female. The main prey species in the stomach of eagle ray was big-eye scad Selar crumenophthalmus. The mangrove whipray had fed on a range of fish (pigface bream, goatfish, silverbellies, silverbiddies and lesser sardine) and octopus.

Re-evaluation of reproductive cycle and fecundity of finetooth sharks Carcharhinus isodon (Valenciennes 1839) from the Northwest Atlantic Ocean, with new observations on ovarian cycle and reproductive endocrinology of biennially reproducing sharks.

To provide updated information on life history for improved fishery management, the reproductive cycle of the finetooth shark Carcharhinus isodon from Northwest Atlantic (NWA) populations was investigated by examining temporal changes in morphology and histology of reproductive organs. Changes in plasma concentrations of gonadal sex hormones in relation to reproductive stage were also examined. Increases in testis width, epididymis head width, plasma testosterone concentrations and occurrence of mature spermatozoa were observed in male sharks between December and April, suggesting a seasonal pattern in reproduction that culminates with copulatory activity in May. Increases in maximum follicular diameter, oviducal gland width, plasma 17β-estradiol concentrations and occurrence of vitellogenic follicles were observed in non-pregnant female sharks during the same time period along with the occurrence of newly pregnant females in May, demonstrating strong synchronicity between male and female reproductive cycles. Pregnant females bearing full-term embryos were also observed in May, indicating that parturition occurs between mid-May and early June and gestation requires 12 months. Only transient temporal changes in follicle size and oviducal gland width were observed in pregnant females, indicating that reproductive periodicity is biennial; nonetheless, a single female exhibiting signs of concurrent vitellogenesis and pregnancy was observed. Mean brood size ± S.D. was 3.9 ± 0.9 offspring/female. Fecundity was not significantly correlated with female size, in part due to an unexpectedly high rate of early embryo mortality, which occurred in 11% of pregnant females, and was more common in larger individuals. Changes in ovarian activity during mid-pregnancy were observed, suggesting possible roles for the ovary in regulating some aspects of early to mid-gestation. This study confirms that earlier characterizations of the reproductive cycle and fecundity in NWA finetooth sharks remain valid for use in fishery management. This study also highlights unusual features of finetooth shark pregnancy (e.g., early embryo death, mid-pregnancy changes in ovarian function) that may have broader relevance to understanding elasmobranch reproduction.

Life-history traits of the spiny dogfish Squalus acanthias in the Adriatic Sea

Pivotal life history traits concerning age structure and reproduction of the spiny dogfish (Squalus acanthias, Linnaeus 1758) were investigated in the Adriatic Sea from mid February 2012 to mid July 2013 and in 2016. The whole sample consisted of 176 females and 150 males, ranging between 217–1025 mm and 219–875 mm, respectively. The individual age, which was estimated using a cross-sectioning technique of the second dorsal-fin spine, ranged from 0 to 13+ years for females and from 0 to 9+ years for males. Based on the length-at-age estimates, the Gompertz growth parameters were L∞ = 1130 mm, k = 0.18 and L∞ = 920 mm, k = 0.24 for females and males, respectively. The size at sexual maturity (L50) was 659 mm for females and 575 mm for males, corresponding to 7.5 and 5.5 years of age (A50), respectively. Mean biennial fecundity was approximately 11 embryos/female and 12 ripe oocytes/female. Mature males occurred during much of the sampling period, while mature females with nearly full-term embryos were exclusively recorded in May 2013 and July 2016. Monitoring of catches conducted in a sample port of the north Adriatic (Chioggia) over the past 20 years has shown fluctuating trends in landings, with peaks during the summer reproductive season.

Ontogeny of escape-hatching decisions: vibrational cue use changes as predicted from costs of sampling and false alarms

As animals develop, their abilities and needs change, altering cost/benefit trade-offs and optimal behavior responses to cues. We tested if ontogenetic changes in information use and environmentally cued hatching decisions of embryos match adaptive predictions, using red-eyed treefrogs, Agalychnis callidryas. These arboreal embryos hatch rapidly and prematurely to escape egg predators, cued by physical disturbance in attacks. Hatching early increases tadpole mortality, and premature embryos use multiple frequency and temporal properties of vibrations to assess risk, avoiding false alarms in benign disturbances such as rain. Because development increases hatchling survival, we hypothesized embryos approaching spontaneous hatching would reduce vibration sampling to reduce egg-predation risk, accepting more false alarms if cues are time-consuming to assess. We designed stimuli to elicit high or low hatching of younger embryos, with the property that reduces hatching either rapidly evident (frequency spectrum or fast temporal pattern) or time-consuming to assess (slow temporal pattern). We developed a new egg-tray vibration playback system to present motion-only cues with minimal disturbance in setup, then used it to compare responses of younger and previously untestable older embryos. The playback duration embryos experienced before or without hatching decreased with age, suggesting reduced vibration sampling. At both stages, hatching responses differed between frequencies, and among temporal patterns; nearly full-term embryos still showed selective hatching responses to cues. Hatching increased developmentally in a stimulus-dependent manner, with the greatest change in response to the slow pattern, as predicted. Developmental changes in discrimination appear well-matched to changing trade-offs, consistent with ontogenetic adaptation of embryo behavior. Animal behavior changes ontogenetically for many reasons, including developing capacities to sense and assess cues and perform actions, adaptive responses to changing costs and benefits, and learning. Hatching is a critical behavior, subject to selection from pre- and post-hatching environments, that is performed during a period of rapid development. Environmentally cued hatching is widespread, and many embryos use vibrations to inform behavior. The egg-tray system we developed enables vibration playbacks to red-eyed treefrog embryos across a broader range of stages than previously possible, facilitating tests of how and why development changes behavior. Playbacks revealed that embryos at different stages assess cues and make decisions differently, with stage-specific responses matching adaptive predictions. This reveals a new level of complexity in embryo information use, motivating and enabling further research assessing the role of adaptive ontogeny and developmental constraint in early behavioral development.

Fryl deficiency is associated with defective kidney development and function in mice.

FRY like transcription coactivator ( Fryl) gene located on chromosome 5 is a paralog of FRY microtubule binding protein ( Fry) in vertebrates. It encodes a protein with unknown functions. Fryl gene is conserved in various species ranging from eukaryotes to human. Although there are several reports on functions of Fry gene, functions of Fryl gene remain unclear. A mouse line containing null mutation in Fryl gene by gene trapping was produced in this study for the first time. The survival and growth of Fryl-/- mice were observed. Fryl gene expression levels in mouse tissues were determined and histopathologic analyses were conducted. Most Fryl-/- mice died soon after birth. Rare Fryl-/- survivors showed growth retardation with significantly lower body weight compared to their littermate controls. Although they could breed, more than half of Fryl-/- survivors died of hydronephrosis before age 1. No abnormal histopathologic lesion was apparent in full-term embryo or adult tissues except the kidney. Abnormal lining cell layer detachments from walls of collecting and convoluted tubules in kidneys were apparent in Fryl-/- neonates and full-term embryos. Fryl gene was expressed in renal tubular tissues including the glomeruli and convoluted and collecting tubules. This indicates that defects in tubular systems are associated with Fryl functions and death of Fryl-/- neonates. Fryl protein is required for normal development and functional maintenance of kidney in mice. This is the first report of in vivo Fryl gene functions. Impact statement FRY like transcription coactivator ( Fryl) gene is conserved in various species ranging from eukaryotes to human. It expresses a protein with unknown function. We generated a Fryl gene mutant mouse line and found that most homozygous mice died soon after their birth. Rare Fryl-/- survivors showed growth retardation with significantly lower body weight compared to their littermate controls. Although they could breed, more than half of Fryl-/- survivors died of hydronephrosis before age 1. Full-term mutant embryos showed abnormal collecting and convoluted tubules in kidneys where Fryl gene was expressed. Collectively, these results indicate that Fryl protein is required for normal development and functional maintenance of kidney in mice. To the best of our knowledge, this is the first report on in vivo Fryl gene functions.

Yolk removal generates hatching asynchrony in snake eggs

Hatching synchrony is wide-spread amongst egg-laying species and is thought to enhance offspring survival, notably by diluting predation risks. Turtle and snake eggs were shown to achieve synchronous hatching by altering development rates (where less advanced eggs may accelerate development) or by hatching prematurely (where underdeveloped embryos hatch concurrently with full-term embryos). In Natricine snakes, smaller eggs tend to slow down metabolism throughout incubation in order to hatch synchronously with larger eggs. To explore the underlying mechanism of this phenomenon we experimentally manipulated six clutches, where half of the eggs were reduced in mass by removing 7.2% of yolk, and half were used as the control. The former experienced higher heart rates throughout the incubation period, hatched earlier and produced smaller hatchlings than the latter. This study supports the idea that developmental rates are related to egg mass in snake eggs and demonstrates that the relationship can be influenced by removing yolk after egg-laying. The shift in heart rates however occurred in the opposite direction to expected, with higher heart rates in yolk-removed eggs resulting in earlier hatching rather than lower heart rates resulting in synchronous hatching, warranting further research on the topic.

Dental ontogeny of a white shark embryo.

Unlike most viviparous vertebrates, lamniform sharks develop functional teeth during early gestation. This feature is considered to be related to their unique reproductive mode where the embryo grows to a large size via feeding on nutritive eggs in utero. However, the developmental process of embryonic teeth is largely uninvestigated. We conducted X-ray microcomputed tomography to observe the dentitions of early-, mid-, and full-term embryos of the white shark Carcharodon carcharias (Lamniformes, Lamnidae). These data reveal the ontogenetic change of embryonic dentition of the species for the first time. Dentition of the early-term embryos (∼45 cm precaudal length, PCL) is distinguished from adult dentition by 1) the presence of microscopic teeth in the distalmost region of the paratoquadrate, 2) a fang-like crown morphology, and 3) a lack of basal concavity of the tooth root. The "intermediate tooth" of early-term embryos is almost the same size as the adjacent teeth, suggesting that lamnoid-type heterodonty (lamnoid tooth pattern) has not yet been established. We also discovered that mid-term embryos (∼80 cm PCL) lack functional dentition. Previous studies have shown that the maternal supply of nutritive eggs in lamnoid sharks ceases during mid- to late-gestation. Thus, discontinuation of functional tooth development is likely associated with the completion of the oophagous (egg-eating) phase. Replacement teeth in mid-term embryos include both embryonic and adult-type teeth, suggesting that the embryo to adult transition in dental morphology occurs during this period. J. Morphol. 278:215-227, 2017. © 2016 Wiley Periodicals,Inc.

Reproductive cycle and maternal-embryonic nutritional relationship of shovelnose guitarfish Pseudobatos productus in the Gulf of California.

Samples of the shovelnose guitarfish Pseudobatos productus were collected on board a vessel and at landings of artisanal commercial fisheries in the Gulf of California from May 2004 to June 2007. Samples of 650 females, 2047 embryos and 484 uterine eggs were examined. The reproductive cycle is annual, ovulation and parturition occur in July, the uterine eggs are in diapause for 9 months (July-March) before an accelerated growth of embryos of 3 months. Histological analyses of the uterine wall of pregnant females suggested that no secretions were used for embryo nourishment. The standard percentage of water content was 48·6% in fertilized eggs and 80·75% in full-term embryos. Dry mass loss during embryonic development was 16·3% and the chemical balance of development was 0·84. This indicates that P. productus is a strictly lecithotrophic, viviparous species, that makes no maternal contribution of nutrients during embryonic development.

Reproductive cycle of Urolophus cruciatus in south-eastern Australia: Does the species exhibit obligate or facultative diapause?

Observations of synchronous rapid growth of embryos and ovarian follicles in pregnant females during the half-year December–May leading to parturition, ovulation, mating, and fertilization suggest Urolophus cruciatus has the capacity for an annual reproductive cycle. Conversely, the higher proportion of the pregnant females in the population carrying eggs than carrying embryos in utero during December–May and all pregnant females in the population only carrying eggs in utero during June–November indicate a longer reproductive cycle. Analysis based on the usual assumptions implies that the species most likely exhibits a biennial cycle with ~18-month period of diapause following ovulation prior to ~6-month period of rapid embryogenesis. However, it is feasible that the period of the cycle is triennial with ~30-month period of diapause or alternatively diapause varies among individuals and varies from year to year. Rather than exhibiting a fixed-term reproductive cycle where obligatory diapause leads to parturition timed every year to provide favourable conditions for neonates, as suggested for several other chondrichthyan species, U. cruciatus may exhibit facultative diapause where the period of diapause and hence the reproductive cycle varies depending on the prevailing environmental conditions or density-dependent factors as described for many terrestrial species. U. cruciatus is highly matrotrophic (>4000 % wet mass gain from ovum to full-term embryo), litter size (1–4) increases with maternal length, sex ratio among embryos is 1:1, and male breeding condition varies seasonally with peak sperm production coinciding with female ovulation.

Superfetation in live-bearing fishes is not always the result of a morphological constraint.

Superfetation is an unusual reproductive strategy that consists of the presence of multiple broods at different developmental stages within a single female. One hypothesis that was proposed to explain its adaptive significance suggests that, in fishes, superfetation is a response to selective pressures that promote a thin and streamlined body shape, such as high-velocity water systems. Superfetation may allow for reduction in ovary size and hence improve streamlining because superfetating females carry few large, full-term embryos at any given time. We tested this morphological constraint hypothesis using reproductive and morphological data from several populations of two viviparous fishes of the family Poeciliidae (Poeciliopsis gracilis and Poeciliopsis infans). We found no evidence to support the morphological constraint hypothesis. In both species the degree of superfetation varied as a function of a complex interaction between source population and female size, and this interpopulation variation was not associated with the velocity of the water current. Contrary to what we expected, females of P. gracilis with more streamlined bodies were observed in rivers where water velocity is slow or moderate. In P. infans the velocity of the water current did not predict variation in body shape. Our results are noteworthy because a previous study which focused on a congeneric species (Poeciliopsis turrubarensis) demonstrated strong support for this hypothesis. However, based on our evidence we conclude that the association among increased superfetation, streamlined morphologies, and fast-flowing environments is not a general rule and that the adaptive value of superfetation may differ among species.

Protective potential of α-tocopherol supplementation against ethanol-induced dysmorphogenesis in postimplantation murine embryos

Abstract Objective To assess the protective potential of α-tocopherol on ethanol-induced dysmorphogenesis in 10.5 embryonic day (ED) mouse embryos. Methods Forty female mice were randomly assigned into control (CON), positive control (ETOH), low-, medium and high-α-tocopherol-supplemented-Ethanol groups (LTOC, MTOC, HTOC, respectively). CON received drinking water without ethanol, ETOH, LTOC, MTOC and HTOC groups received 20% ethanol in drinking water. The supplemented groups were given respective dosages of α-tocopherol, 0.410, 0.819 and 1.640 mg/g body weight, at 14 days before mating until the 9th day of gestation. The 10.5 ED embryos were assessed for embryo weight, head- and crown-rump length, and morphological scoring of brain and sensory vesicles, flexion and somites. The embryo yield was assessed by counting the number of full-term developed embryos from the bulging implantation sites while resorption was assessed by counting the bulging implantation sites but without formed embryos. Results The weight and head- and crown-rump length of the embryos from the α-tocopherol supplemented groups were comparable to the control. These were significantly higher than that of positive control ( P P P Conclusion The medium and high dosages of α-tocopherol exhibited a protective effect on ethanol-induced dysmorphogenesis.

Population structure of the piked dogfish Squalus acanthias (Elasmobranchii: Squalidae), with preliminary reproductive observations

Squalus acanthias has been poorly studied in Uruguay, though reproductive studies have been carried out in Argentina in the decades of 1970–1980. The aim of this work was to analyze the population structure and the reproductive biology of S. acanthias along the Uruguayan continental shelf (south-western Atlantic Ocean) between 1995 and 2010. Total length (TL) ranged from 30–95 cm for females (n = 1,323) and 25–81 cm for males (n = 999). Significant differences in the TL frequency distributions between sexes and among seasons were detected, with abundances in the magnitude of up to 5,000 individuals/nm2. Length at first maturity (TL50) was 58.3 cm in males and 70.4 cm in females. Ovarian and uterine fecundity were 2–14 and 1–14, respectively, and both were positively correlated with maternal TL. Females with candled embryos were recorded in autumn. Embryo TL was significantly greater in winter, which is when parturition is likely occurring. Full-term embryos had a TL of 22–25 cm. Sex ratio of embryos was close to parity. Ovarian vitellogenesis was observed to be occurring concomitantly with gestation.

Abstract NG05: Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors

Abstract NG05: Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors

Maturation, fecundity and reproductive cycle of spiny dogfish, Squalus acanthias, in the Adriatic Sea

We provide the first detailed information on the reproductive traits of the endangered spiny dogfish (Squalus acanthias) in the Adriatic Sea, based upon 224 specimens (132 females and 92 males) collected onboard of commercial bottom trawls between 2005 and 2007. The morphometry of gonads, gonadosomatic index (GSI) and histological examination of gonads were used to analyse maturation and gonadal development of the species. The length at 50% maturity was attained at 504 mm for males and 725 mm for females. Ovarian fecundity ranged from 4 to 18 follicles (mean±SD: 10.8±4.5) and uterine fecundity ranged from 6 to 18 embryos (mean±SD: 10.1±3.9). Total length of embryos with absorbed yolk sacs ranged between 200 and 215 mm. The GSI and the high proportion of mature spermatocysts in the testes suggests that a majority of mating activity occurs in June, November and December, while the seasonal distribution of the largest ova and full-term embryos indicate that ovulation and parturition occur during the summer. In comparison with other study areas, spiny dogfish in the Adriatic Sea attained sexual maturity at smaller sizes and obtained higher fecundity values than fish from other regions.

Can a Threshold Value Be Used to Classify Chondrichthyan Reproductive Modes: Systematic Review and Validation Using an Oviparous Species

The maternal-embryonic nutritional relationship in chondrichthyans has been poorly explored. Consequently, accurately discerning between their different reproductive modes is difficult; especially lecithotrophy and incipient histotrophy. This present study is the first to assess changes in mass throughout embryonic development of an oviparous chondrichthyan other than Scyliorhinus canicula. Heterodontus portusjacksoni egg cases were collected and used to quantify the gain or loss of wet mass, dry mass, water content, inorganic and organic matter from freshly deposited eggs (without macroscopically visible embryos) to near full-term embryos. A loss in organic mass of ∼40% found from this study is approximately double the values previously obtained for S. canicula. This raises concerns for the validity of the current threshold value used to discern between lecithotrophic and matrotrophic species. Accordingly, 26 studies published in the primary literature between 1932 and 2012 addressing the maternal-embryonic nutritional relationship in sharks were reviewed. Values for changes in mass reported for over 20 different shark species were synthesised and recalculated, revealing multiple typographical, transcribing, calculation and rounding errors across many papers. These results suggest that the current threshold value of −20% established by previous studies is invalid and should be avoided to ascertain the reproductive mode of aplacental viviparous species.

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.

Biennial reproductive cycle in an extensive matrotrophic viviparous batoid: the sandyback stingaree Urolophus bucculentus from south‐eastern Australia

Urolophus bucculentus, the largest urolophid species found in southern Australia, exhibits a biennial reproductive cycle. Ovulation occurs during October to January followed by a 15-19 month period of gestation followed by parturition during April to May and a short rest period while the ovarian follicles continue to develop for subsequent ovulation. Male breeding condition peaks during April to June to coincide with the period of parturition. Urolophus bucculentus has the highest matrotrophic contribution reported for any urolophid species, with a mean wet mass gain from egg in utero (4 g) to full-term embryo in utero (250 g) of c. 6250% (maximum c. 7200%), and perhaps explains the biennial female reproductive cycle where 50% of females contribute to each year's recruitment. Litter size (one to five) increases with total length (L(T) ). Females reach a longer maximum L(T) (L(Tmax) ) than do males (885 v. 660 mm). The L(T) at maturity for males and females at 50% mature (L(T50) ) is c. 414 mm (63% of L(Tmax) ) for males and c. 502 mm (57% of L(Tmax) ) for females, length at maternity indicates that recruitment production occurs later in life at c. 632 mm L(T) (71% of L(Tmax) ).

Epigenetic reprogramming of embryos derived from sperm frozen at −20°C

Cryopreservation of spermatozoa is a strategy that has been used to conserve the sperm of animal species and animal strains that are valuable for biomedical research. A simple method for preserving spermatozoa after application of intracytoplasmic sperm injection (ICSI) is much needed. It has been shown previously that spermatozoa frozen at -20°C can activate oocytes and support full-term embryo development. However, epigenetic reprogramming could be affected by the environment and by the in vitro manipulation of gametes. Here, we investigated embryo epigenetic reprogramming including DNA methylation and histone modification, in embryos derived from sperm preserved at -20°C without cryoprotectants. The results showed that although both fertilization and embryo developmental competence were decreased, the dynamic epigenetic reprogramming of embryos derived from frozen sperm was similar to the reprogramming of embryos derived from fresh sperm. The results reported in this study indicate that sperm frozen without cryoprotectant is epigenetically safe for ICSI.

Quantification of the maternal–embryonal nutritional relationship of elasmobranchs: case study of wobbegong sharks (genus Orectolobus)

The present study used wobbegong sharks (genus Orectolobus) to assess the threshold value proposed by previous research to categorize strict lecithotrophic from incipient histotrophic species. Totals of 236 and 135 ornate wobbegong Orectolobus ornatus and spotted wobbegong Orectolobus maculatus, respectively, were collected from the New South Wales commercial fishery between June 2003 and May 2006. Eight pregnant gulf wobbegong Orectolobus halei were also recorded outside the sampling period for the first time. The three species were reproductively synchronous with a gestation of c. 10-11 months. Embryos started to be macroscopically visible during January and external yolk sacs were fully absorbed by June to July when embryos were c. 200 mm total length (L(T) ). Internal yolk sacs were first observed during April to May when embryos were c. 160 mm L(T) , reached a peak during June and persisted in embryos immediately prior to parturition. The total wet mass from uterine egg to full-term embryos increased by 44-89% and 45-62%, whereas the total organic mass decreased by 32-33% and 26%, for O. ornatus and O. maculatus, respectively, suggesting that these species are strict lecithotrophic yolk-sac viviparous sharks with no maternal nutrient input. A review of the literature identified various issues and suggested that the previously proposed organic mass loss threshold value separating strict lecithotrophic species from incipient histotrophic species might not be appropriate. Instead, it is recommended that a combination of methods (e.g. estimation of organic mass gain or loss between ovarian egg and developed embryo, histology and electron microscopy of the uterus, radio-tracer assay and uterine fluid analysis throughout gestation) is used to discern between strict lecithotrophic and incipient histotrophic species.

Reproductive biology of the eastern shovelnose stingaree Trygonoptera imitata from south-eastern Australia

In applying a quantitative approach to the reproduction of Trygonoptera imitata, the present study contributes to understanding the wide diversity in the reproductive biology of the family Urolophidae and provides insights to help determine phylogenetic relationships. This localised species is taken as bycatch in several inshore fisheries and potentially impacted by a range of other anthropogenic pressures, including introduced species, particularly in shallow-water pupping areas. T. imitata can be characterised as a species of comparatively low matrotrophic histotrophy with an extended period of relatively large eggs in utero (5–8 months) followed by rapid growth of the embryos (4–6 months). The reproductive cycle is annual with parturition occurring during late-February–April, followed immediately by ovulation. Mean size-at-birth is ~225 mm total length and there is a ~1000% gain in mean wet mass from egg (15 g) to full-term embryo in utero (150 g), the lowest reported for any viviparous batoid. Litter size increases with maternal length, reaching a maximum of seven, and sex ratio of embryos is 1 : 1. Maximum length and estimates of the maturity–ogive parameters l50 and l95 are similar for females and males.