The intra-ovarian presence of ootids, i.e. female gametes that have completed meiosis, is considered exceptional in the animal kingdom. The present study explores the first such case to be reported in a sea cucumber (Echinodermata: Holothuroidea). In the overwhelming majority of animals, including holothuroids, oocytes (i.e. immature female gametes) that are developing in the ovary undergo a primary arrest at the prophase stage of meiosis, which may last from days to decades. In free-spawning taxa, this arrest is normally lifted only during or shortly before transit in the gonoduct, when gamete release (spawning) is imminent. However, oocytes of the holothuroid Chiridota laevis were discovered to have resumed the second meiotic division including the completion of germinal vesicle breakdown and polar-body expulsion inside the ovary, effectively reaching the ootid stage concomitantly with ovulation (i.e. escape from follicle cells) prior to spawning. The potential drivers and significance of this exceptionally rare case of full intra-ovarian oogenic maturation are discussed.

The reproductive cycle of Marphysa sanguinea is described for a population at Mount Edgecombe, Plymouth, near the type location in Southwest England, using a data set obtained previously (October 1999 to September 2000). The species is iteroparous without schizogamy, spawning prior to October 1999 and during a short breeding season in 2000 from end August through September. The sexes are separate with a sex ratio of 1:1. Mature oocytes and spawned eggs are 215 μm in diameter and spermatozoa of the ectaqua sperm type. Mature gametes of both sexes are discharged through paired coelomoducts, and the diploid chromosome number is 28. Proliferation of new coelomic gametes from paired gonads began within a month of spawning and continued for 8–9 months but ovulation was suppressed in June and July. Attempts to undertake fertilisation using spawned oocytes and active spermatozoa were unsuccessful. The size of discharged oocytes suggests a short pelagic larval duration of a few days. This is the first publication about the reproduction of this species, and our results suggest that M. sanguinea is restricted to intertidal areas in SW England, NW France and southern North Sea. The highly synchronised pattern of reproduction observed is not compatible with a quasi-cosmopolitan species range indicating that this species has been mistakenly reported from around the world. Future studies of the genus should combine rigorous taxonomy with observations of reproduction to facilitate comparison among Marphysa spp.

Estuarine ecosystem conditions actively influence the early life stage of fishes. This study reports how environmental factors influenced the ichthyoplankton in a tropical estuary within an Environmental Protection Area by comparing the structure and composition of fish eggs and larval assemblages. A total of 1672 fish larvae and 486 fish eggs were collected. Higher densities of larvae were recorded for Engraulidae, Characidae, Clupeidae, Gerreidae, Mugilidae and Atherinopsidae, and higher egg densities of the families Mugilidae, Clupeidae and Engraulidae were found. The spatio-temporal variations were determined by the environmental predictors salinity, pH, dissolved oxygen and temperature, with salinity influenced by precipitation as one of the main predictors of the distribution of ichthyoplankton. During the rainy season, greater densities of eggs were recorded in the upper and intermediate zones, mainly Characidae and Engraulidae; in the dry season, in the lower zone, there was a greater density of larvae, particularly Atherinopsidae and Mugilidae. The information provided in the present study contributes to our knowledge of nursery habitat requirements for the initial development of marine migrant and resident species in tropical estuaries.

The reproductive characteristics of co-occurring freespine flathead, Ratabulus diversidens, and mud flathead, Ambiserrula jugosa, that interact with fisheries across continental shelf waters of eastern Australia were examined. Samples were collected across three depth strata and two locations on a monthly basis over two years. Males of both species matured younger and at smaller total lengths (TL) than females. Estimated TL and age (years) at maturity (L50 and A50, respectively) of R. diversidens also varied between locations, but differences were not related to differential growth. Although some mature individuals of both species occurred year-round, they were most prevalent and gonadosomatic indices greatest, between the austral spring and autumn. Mature R. diversidens almost exclusively occurred in deeper offshore waters, whereas the opposite was evident for A. jugosa. Both species displayed asynchronous oocyte development, and were thus considered capable of spawning more than once throughout each spawning season. Potential batch fecundity was positively related to TL for R. diversidens, but not A. jugosa, possibly due to the small size of the latter species. The sex ratios for R. diversidens varied between locations and length categories, and like A. jugosa the larger categories were skewed towards females, a result of divergent growth between sexes. Macroscopic and microscopic evidence indicated both species were gonochoristic. The data provide new information for fisheries management consideration and contribute to the data-poor international knowledge base of platycephalid biology.

The study sought to investigate the chronology of events and timing of embryogenesis, as well as breeding performances of three strains of Heterobranchus longifilis from Nigeria. Fish samples were collected from Benue River in Makurdi, Niger River in Onitsha, and Rima River in Sokoto for this study. Induced spawning of the strains was carried out so that egg development could be tracked from fertilization to hatching using a simple microscope. The microphotographs obtained showed that the embryogenesis of the strains followed a similar pattern to those of other members of the family Clariidae, however with changes occurring in the specific timing of the sequences of events (i.e. interstrain and interspecies differences). When the different strains were compared, the study noted similarities (P > 0.05) in the overall breeding performance (except for fertilization rate), survival at different stages of development, timing of embryogenesis, and larvae characteristics. The outcomes of this study, therefore, provide baseline information on what genetic improvement of the species through strain crossing can be attempted in future studies.

Hypleurochilus fissicornis is a resident species of the intertidal and subtidal zones of Mar del Plata, Argentina. The specific reproductive biology was studied by means of both microscopic and macroscopic analyses. A total of 212 males and 223 females were analysed. Specimens were dissected and their gonads and livers were removed. The gonadosomatic and hepatosomatic indexes and the condition factor were calculated on a monthly basis. Hypleurochilus fissicornis breeds in rocky intertidal areas, and exhibits low fecundity with benthic eggs and parental care. Size at first maturity (L50) was estimated at 53.66 and 55.83 mm total length for females and males, respectively. The spawning season takes place between December and April.

Anguillid leptocephali of three Congridae species (Conger conger, Ariosoma balearicum and Gnathophis mistax) were caught as bycatch of pelagic trawls during acoustic surveys targeting small pelagic fish species in the southern Adriatic Sea, carried out under the framework of the Italian MEDIAS project (western side) and its extension in the ambit of the FAO AdriaMed project (eastern side). Results refer to the findings of Congridae leptocephali during surveys conducted in 2011, 2014, 2015 and 2016. A total of 25 specimens were caught and analysed (morphological features and pigmentation patterns). Leptocephali of Conger conger were found in the range of 8.4–13.1 cm total length (TL) (between 50 and 132 m depth), Ariosoma balearicum from 9.7–12.2 cm TL (between 50 and 128 m depth) and for Gnathophis mystax in the range from 6.4–11.7 cm TL (between 40 and 79 m depth). The results indicate that the southern Adriatic Pit could be the spawning area of these species in the Adriatic Sea. Present data represent a contribution to existing knowledge about the ecology of leptocephali from the Congridae family in the southern Adriatic Sea, and also indicate the existence of differences in morphometric parameters between different areas, that is, the possibility of the existence of new geographic lines within the genus Ariosoma in the Adriatic Sea.

Atlantic bonito, Sarda sarda, is one of the representatives of the Scombridae family in the Adriatic Sea. Larvae and juveniles have been found and described in the area, but no information has been published regarding adults spawning in the Adriatic Sea. To explore the strong possibility that Atlantic bonito are reproducing in the Adriatic Sea, 122 specimens of adult Atlantic bonito were collected from a purse seine net ‘palamidara’ over four seasons in 2017. The fork length of the analysed specimens varied from 37.5 to 60.8 cm, with a mean of 48.83 ± 5.59 cm, while total body weight varied between 742.68 and 3102.59 g, with a mean value of 1700.49 ± 543.82 g. Gonadosomatic index values showed an increasing trend from autumn (0.123 for males, 0.897 for females) until spring, while in the summer, they reached their maximum values (3.609 for males, 5.604 for females). This trend was also confirmed by histological and macroscopic analyses of gonads, which suggested that the Atlantic bonito spawning season is in the spring-summer in the Adriatic Sea. Hence, this confirms that this species is spawning in the Adriatic Sea.

The synchrony of spawning is of paramount importance to successful coral reproduction. The precise timing of spawning is thought to be controlled by a set of interacting environmental factors, including regional wind field patterns, timing of the sunset, and sea surface temperatures (SST). Climate change is resulting in increased SST, which is causing physiological stress in corals and could also be altering spawning synchrony and timing. In this study, we examined the effect of increasing seawater temperature by 2°C for 1 month prior to the predicted spawning time on reproduction in the coral Acropora digitifera. This short period of elevated temperature caused spawning to advance by 1 day. In animals incubated at elevated temperature, egg number per egg bundle did not change, however, egg volume significantly decreased as did sperm number. Our results indicate that temperature is acting both as a proximate cue to accelerate timing and as a stressor on gametogenesis to reduce fecundity. This finding suggests that increasing SSTs could play a dramatic role in altering reproductive timing and the success of corals in an era of climate change.

This study describes for the first time the reproductive traits of the warm-water pompano, Trachinotus ovatus. Specimens were sampled from landings by artisanal fishing vessels in the NW Mediterranean. Monthly collections, from July 2010 through to September 2012, yielded 226 individuals (118 females and 108 males). The size at 50% maturity (L50) was estimated at 30.9 and 29.1 cm TL for females and males, respectively. Specific reproductive traits, such as oocyte size-frequency distributions, presence of recent post-ovulatory follicles along with oocytes in the final phases of gonadal development, and massive atresia in post-spawning individuals, indicated that pompanos are multiple batch spawners with asynchronous oocyte development and indeterminate fecundity. Monthly variations in the gonadosomatic index and in the phases of gonadal development indicated July and August as the spawning season. There were also noticeable inter-annual variations in spawning phenology, mean diameters of the oocytes, relative batch fecundity and eggs quality, all of which corresponded to changes in sea surface temperatures. This study enhances our understanding of the need for research into the reproduction of warm-water species, which are currently expanding into the increasingly warmer waters of the world's more northerly seas and oceans.

The reproductive biology of the lane snapper, Lutjanus synagris, was evaluated from 770 specimens (434 females and 336 males) obtained on the Abrolhos Bank, eastern Brazil, between May 2005 and October 2007. Total length ranged from 14.7 to 56.0 cm for females and from 16.5 to 54.3 cm for males, with size composition not varying significantly between sexes. Five distinct maturity stages were identified based on macroscopic and histological examination of the gonads. Mean value of the gonadosomatic index (GSI) for females peaked in September and October, with a secondary peak in February and March. Histological analyses confirmed the reproductive cycle inferred by GSI variation. Asynchronous-type ovarian development was observed, and batch fecundity ranged from less than 104,743 oocytes for a 25.5 cm female of to 568,400 oocytes for a 56.0 cm female (250.0 and 2260 g, respectively), with an average of 345,700 oocytes. The reproductive parameters obtained for L. synagris in the Abrolhos Bank were similar to those reported in studies in northern Brazil and the north-west Atlantic. The species is an important fishery resource in the study region, and management measures are needed before the species becomes overfished. Exploitation occurs largely during spawning aggregations, a situation that has caused other lane snapper populations (and congeners) to decline acutely elsewhere. Our results provide support for size limits and seasonal spawning closures on the Abrolhos Bank, a region that sustains artisanal fisheries involving >20,000 fishermen.

The aim of the present study was to characterize biopsied and stripped oocytes from the Brazilian endangered teleost pirapitinga (Brycon nattereri) using histochemical and morphological analyses. Biopsied oocytes had a mean diameter of 2.225 mm (modal diameter: 2.312 mm), complete vitellogenesis and a central or slightly eccentric nucleus. Neutral polysaccharides were detected in the follicular cells, zona radiata and yolk globules, while acidic polysaccharides were detected in the follicular cells and cortical alveoli. Ten out of the 19 females treated with two doses of carp pituitary extract (cPE) released oocytes, which were also analysed. Stripping occurred 292 ± 39 degree-hours after the second dose of cPE and led to a mean spawning weight of 36.2 g, 10% spawning index, 241 oocytes/g of ova, 8222 oocytes/female and 23 oocytes/g of body weight. Stripped oocytes had a mean diameter of 2.33 mm and a mode at 2.375 mm, were weakly adhesive and coloration ranged from wine to brown. Under scanning electron microscopy, stripped oocytes exhibited a single funnel-shaped micropyle located at the animal pole and a zona radiata that measured 7.7 μm in thickness with eight pore canals/μm2. Oocyte morphology in Brycon nattereri is similar to that found in other species of the genus, except for the larger size and weaker adhesiveness. These findings provide essential information for a better understanding of the reproductive biology of B. nattereri and the establishment of conservation measures for this threatened species.

Based on the economic and ecological relevance of Brycon amazonicus, the goal of this work was to describe the diameter of oocytes and eggs of this species, as well as the chronological embryonic development. The material was provided by Buriti fish farm, Nova Mutum – MT, Brazil. Samples of both oocytes and eggs were obtained from extrusion to hatching. The material was fixed and measured under stereomicroscope, and the samples were divided for light microscopy or scanning electron microscopy (SEM) analyses. At extrusion, the oocytes were bluish green. The frequency distribution of oocytes revealed that 87.7% of them ranged from 1.11–1.30 mm in diameter. During incubation, the total diameter of the eggs increased from 1.22 ± 0.04 mm to 3.06 ± 0.46 mm in the first 60 min post fertilization (PF), and growth ceased at 180 min PF. Between 10–30 s PF, most eggs were fertilized and fertilization cones were observed from 10 s onwards after gamete activation. The main fertilization events took place asynchronically and spermatozoa were visualized in the micropyle vestibule up to 90 s PF. The first cell was formed in the centre of the blastodisc 20 min PF. The morula stage was identified 2 h PF and, 3 h later, 70% of the yolk was covered by the blastoderm; the blastopore was almost entirely closed at 6 h PF. The cephalic and caudal regions of the embryo could be defined 8 h PF and hatching occurred after 13 h of embryonic development. The larvae hatched with undifferentiated organic systems and with a large yolk sac, free from swimming abilities or visual acuity.

The annual gametogenic cycle in the blue mussel, Mytilus edulis L. was investigated from May 2010 to May 2011 in two locations in north-western Iceland. Food availability (chlorophyll-a) was high in early spring at both sites, with a summer maximum in July in Steingrimsfjördur but an autumn maximum in September in Patreksfjördur. Gonad development started in November at both sites, with ripe gametes still visible in the follicles, and continued throughout the year, except for a very short time prior to spawning in Steingrimsfjördur. Gametes developed mostly between November and May. Spawning was protracted, lasting from July to early winter at both sites. The main spawning events occurred from August (11.7°C) to October (9.4°C) in Patreksfjördur, but from July (9.8°C) to October (8.6°C) in Steingrimsfjördur

The relative growths of Persephona lichtensteinii, P. mediterranea, and P. punctata were investigated on the south-eastern Brazilian coast, focusing on differences in the growth rates between immature and mature phases, the onset of morphological sexual maturity, and the breeding seasons of these species. Crabs were collected every two months from January 1991 through to November 1992, from a shrimp fishing boat equipped with two otter-trawl nets. Significant differences in the patterns of body growth were observed between immature and mature phases of all three species. Changes in the growth rates of the chelipeds (males) and abdomen (females) observed for P. lichtensteinii, P. mediterranea, and P. punctata, seem to be related to the puberty moult for both sexes. Males of P. mediterranea and P. punctata reached larger mean sizes of carapace width than females, whereas no difference was recorded for P. lichtensteinii. The body size at which 50% of males attained sexual maturity was also larger in P. mediterranea and P. punctata, and smaller in P. lichtensteinii. The absence of a pronounced sexual dimorphism and the size at the onset of sexual maturity observed only for P. lichtensteinii might be explained by distinct reproductive strategies of males. The presence of ovigerous females during the entire sampling period suggests that all three species have a continuous reproduction pattern at the Ubatuba region. Future studies on the population structure, functional maturity, and mating system should improve the understanding of factors driving the biology and ecology of these species at a subtropical region.

Serpulid polychaetes are often important components of marine communities, yet current knowledge of serpulid reproduction, development and settlement is largely based on the study of only a few species. This study examined whether spawning and sexual development of the mid-intertidal serpulid Spirobranchus cariniferus are typical of patterns observed in other serpulids, and also examined the effect of diet on larval development and identified cues that induce metamorphosis. Populations of S. cariniferus on the east and west coasts of New Zealand's North Island had an extended spawning season with a high proportion (75–100%) of individuals carrying ripe gametes at any given time from the late spring to early autumn, consistent with other serpulid species. However, contrary to proposed patterns of sexual development in serpulids, sex-ratios and average male and female body masses suggest S. cariniferus are not protandric hermaphrodites. A diet experiment revealed that larval growth was fastest when provided with a mixed diet of three algal species. Solutions of 3-isobutyl-1-methylxanthine at a concentration of 10−4 M were potent inducers of metamorphosis in S. cariniferus larvae, revealing that competence is reached by 13–15 days after fertilization. When exposed to surfaces coated with conspecific tube or tissue homogenates, 6% of competent larvae settled and metamorphosed on surfaces coated with tube homogenate whereas none settled on tissue homogenate or in the controls, suggesting specific cues are required for settlement and the likely presence of a settlement cue in the tubes of adult worms, consistent with the highly gregarious distribution of the species.

Diel rhythms in feeding and spawning were investigated in Centropages tenuiremis from Xiamen Bay in March to May, 2006. Circular statistics were used to determine the peak time of spawning. The results showed that the feeding activities of females were stably higher at night-time, and there was a remarkable earlier shift in spawning peak time with warmer seawater. Thus, the lag times between peak times of gut pigment content and spawning were shortened with the increase of temperature. It suggested that there was a direct effect of feeding rhythms on egg production variations in copepods, and the seawater temperature would work on the converting time and then influence the spawning peak time. So the effect of temperature cannot be ignored in the investigation of the effects of feeding on egg production.

An egg mass of Loligo forbesi was observed in the field for the first time while conducting a remotely operated vehicle dive at a depth of 370 m, off the São Jorge Island (Azores, north-east Atlantic). This observation allowed the confirmation of two hypotheses previously suggested for the reproduction of this species: (i) that in the Azores this species spawns deeper than the previously recorded 144 m; and that (ii) it is likely that this species prefers to spawn within cavities. The way the observed egg strings suspended from the roof of a cavity, underneath a rocky block, surrounded by sediment, is a feature that interestingly seems to be shared between L. forbesi (in the Azores, all the previous naturally-laid egg masses were recovered from within cavities) and L. vulgaris that inhabit shallower waters off the Madeira archipelago.

Halicarcinus planatus is the only species of the genus occurring at the southern tip of South America, in sub-Antarctic, cold-temperate waters. Previously it has been shown that the population from the estuary of the Deseado River presents a spatial segregation by sex, a complete overlapping of sizes among adolescents and adult females. Females go through two reproductive seasons, separated by a resting period during late summer and early autumn, and 7 to 8 spawns are produced following a single mating. The aims of the present work were to evaluate the duration of the embryonic development until hatching during successive spawning, to determine the fecundity and to discuss the adaptive reproductive strategies of this population. Breeding occurs from nearly 2°C to above 16°C. The incubation period lasts nearly 100 days in winter and between 30 and 40 days in summer. The fecundity ranged from 210 to 2150 eggs, it differs between successive spawning and a positive relationship was found between fecundity and carapace width. This population has the highest fecundity compared to other populations, but also compared to other species of the genus. The high number of successive spawns is directly linked to the increase of seawater temperature by the end of spring and during summer. This way, this species would be very well adapted to live in the more temperate waters of Patagonian coasts.

We conducted a histological investigation of the ovaries and testes during the gametogenesis and spawning in the giant jellyfish Nemopilema nomurai, which has bloomed in East Asian marginal seas almost annually since 2002. Oocytes arising from the ovarian epithelium make intimate contact with special epithelial cells, called trophocytes, which have microvilli on the subgenital sinus side, Golgi complexes and vesicles in the cytoplasm. In the early vitellogenic stage, yolk bodies occur in the ooplasm adjacent to the trophocytes, suggesting that the trophocytes transfer nutrients from the subgenital sinus to the oocyte. Later, yolk bodies are formed by the Golgi complexes in the entire ooplasm and accumulate until the oocyte matures. In the late vitellogenic stage, the oocyte separates from the trophocytes and forms microvilli on its surface, indicating nutrient uptake from the surrounding mesoglea. Nutrient support from the trophocytes in the early vitellogenic stage may make the oocytes mature rapidly after medusae are physically damaged. Microvilli-rich epithelial cells also associate with sperm follicles where spermatocytes arise from the follicle cells and accumulate, but their function in nutrient uptake is possibly less than that of trophocytes according to their morphology. During ovulation, which takes 1.5 hours after light exposure, trophocytes separate from each other and make an ovulation pit where the oocyte passes out to the subgenital sinus with the surrounding basal lamina. Spermiation occurs 5–20 minutes after light exposure, and spermatozoa are liberated through the spermiation pit that was formed by which the microvilli-rich cells dissociate. The trophocytes in ovaries and microvilli-rich cells in testes have important roles not only in the gametogenesis but also in the spawning of N. nomurai.