The present study described the gametogenesis and assessed the pattern of energy storage throughout the reproductive cycle of the golden carpet shell (Polititapes aureus) from the Ria Formosa lagoon (southern Portugal). Monthly sampling was performed for two years (March 2016–February 2018) and the study was based on gonad histology, complemented by the estimation of the mean gonadal index, body condition index and biochemical composition. The species’ reproductive cycle presented a seasonal pattern, with a resting period mainly between October and January and gametogenesis beginning around February–March. The spawning season of P. aureus was shorter in 2016 (June–September) than in 2017 (May–October). Furthermore, ripe individuals were very scarce (1.3%) in 2017 compared with the previous year (11.4%). Mean gonadal index (GI) reflected the species’ reproductive cycle and the body condition index (CI) and biochemical composition of the individuals exhibited high variation between years. Regarding the biochemical composition, proteins ranged between 190.6 and 595.2 μg mg−1, glycogen from 5.7 to 102.6 μg mg−1 and total lipids between 31.6 and 80.7 μg mg−1. The reproduction of P. aureus was strongly influenced by fluctuations in both seawater temperature and chlorophyll a, as reflected through the temporal variation in the gonadal cycle, condition index and biochemical composition. Overall, the information gathered in this study is valuable to propose scientifically based harvesting management measures for the long-term sustainable exploitation of this shellfish resource, further reinforcing the importance of implementing adaptive fishery management strategies to cope with global climate change.

Understanding variations in the reproductive cycle of commercial and ecologically important bivalve species is essential to address fisheries management and climate oscillation issues. Spatial and temporal trends in the reproductive cycle of Callista chione were analysed using standard histological procedures and gonadosomatic index (GSI) for two consecutive years at two coastal sites in the Adriatic Sea. Reproductive output and fecundity were analysed quantitatively to gain better insight into the seasonal energy balance with respect to gametogenesis. A seawater temperature difference of ~4°C between the two sites likely influenced the onset and duration of spawning. At Cetina (milder temperatures), spawning was prolonged and occurred between spring and July, whereas at Pag there was only one main spawning peak in July. Both histology and GSI showed similar trends, indicating GSI to be a reliable method for analysing the main characteristics of the reproductive cycle. Conversely, the use of the body mass index (BMI) as an indicator of gonad development should be addressed carefully. Intraspecific variation in energy allocation between populations suggested life strategies modified to different habitat conditions. A higher reproductive investment and output in the Pag population directed gonadal resorption to ensure the generation of a new cycle, whereas the higher fecundity at the Cetina site indicated the production of gonads from newly available food. These results suggest successful physiological acclimatization to recent increasing temperatures.

Literature about fish kidney peroxisomes is scarce. To tackle this caveat, a stereological approach on renal peroxisome morphological parameters was performed for the first time in a fish, establishing correlations with maturation stages as it was previously done in brown trout liver. Three-year-old brown trout males and females were collected at the major seasons of their reproductive cycle. Trunk kidney was fixed and processed for catalase cytochemistry. Classical stereological methods were applied to electromicrographs to quantitate morphological parameters. Different seasonal variation patterns were observed between genders, and between renal proximal tubule segments I and II. In males, peroxisomes from proximal tubule segment II had a relatively higher volume and number in May, being individually bigger in February. Females presented similar trends, though with less marked variations. Overall, males and females did not show exactly the same seasonal patterns for most peroxisomal parameters, and no correlations were found between the latter and the gonado-somatic index (GSI). Hence, and despite the variations, the morphology of renal peroxisomes is not strictly correlated with gonad maturation kinetics, therefore suggesting that kidney peroxisome morphology is not seasonally modulated by sex steroids, like estradiol, as it seems to happen in liver peroxisomes.

Reproductive aspects of the sea cucumber Athyonidium chilensis were studied over a year in Valdivia, Chile, through gonad index (GI) analysis, macro- and microscopic analysis of the gonads, fecundity and size at first sexual maturity estimations. We also explored the reliability of live size estimators for their use in fisheries. Athyonidium chilensis showed continuous gametogenesis and spawning individuals could be found throughout the year. However, spring was the main reproductive time, where an important GI decrease coincided with enhanced spawning activity evidenced through histology. GIs recovered in summer, and new signs of enhanced spawning activity were observed towards autumn (April 2008). GI peaks were observed in August 2007 and March 2008 for females (22.8 and 24.4% respectively) and September 2007 and March 2008 for males (31.9 and 25.9% respectively). Low mean GIs occurred in May and December 2007 for females (15.2 and 11.6% respectively) and May and October 2007 for males (12.7 and 14.1% respectively). Males reached sexual maturity at a smaller size than females (males: 21.2 g, females: 43.7 g eviscerated weight), and mature females showed a high mean absolute fecundity for a species with lecithotrophic larval development (6.31 × 105 ± 1.97 × 105 SD). For fisheries, we recommend a minimum catch size over 237.89 g drained weight to ensure that caught individuals are sexually mature. This study provides relevant information for the conservation and fishery management of A. chilensis. Continuous gametogenesis and high fecundity make this species particularly suitable for aquaculture in southern Chile.

The reproductive biology of the pelagic thresher shark Alopias pelagicus, was analysed based on 241 individuals (101 males and 140 females). Samples were collected from April 2005 to February 2006, from the artisanal fishery in Manta, Ecuador. Males ranged from 68 to 183 cm precaudal length (PL); females ranged from 70 to 180 cm PL. In embryos, sexual proportion was 1F:1M; while in adults the proportion was 1.4F:1M, which suggests sexual segregation in maturing individuals. We showed differences in the development of reproductive structures according to the reproductive condition, and in males the size at maturity occurs at 144.3 cm PL and in females at 151.4 cm PL. We recorded 33 pregnant females that presented one embryo in each uterus in different developmental stages. The results of this study provide information on reproduction of the species that will help to establish an appropriate fisheries management.

The azooxanthellate sun corals Tubastraea coccinea and T. tagusensis are invasive species which were introduced into Brazilian shallow-water tropical rocky reefs by oil and gas platforms. Both species are simultaneous hermaphrodites and brooders. Histological analysis shows a continuous reproduction with the presence of different stages of development of oocytes, spermatic cysts and larvae occurring together in the same polyps (overlapping). Gametogenesis, embryogenesis, planulation and settlement were observed. Although most of the colonies showed only oocytes, none had only testes. Spermatic cysts were observed in 8.3% of T. coccinea colonies and in 5.5% of colonies of T. tagusensis. The maximum diameter of oocyte of T. tagusensis (1252.5 µm) was greater than T. coccinea (901.8 µm) and mature spermaries 700 µm in diameter formed the typical arrangement of ‘bouquets’. Although all colonies showed oocytes throughout the year, two reproductive peaks of 3–4 months duration were observed. The larvae of T. coccinea and T. tagusensis had a competency period of 18 d in aquaria and settled near the parental colony. The investigation of gametogenesis, temporal patterns of reproduction, fecundity and sexual maturation helps to explain the rapid expansion in to new habitats and high population growth in these invasive sun corals.

The pollack, Pollachius pollachius, is an important commercial species for the Spanish artisanal fleet in Atlantic Iberian waters. This study provides information on the reproductive biology of the species, including length at maturity, reproductive cycle and gamete development pattern based on histological methods. A collection of 622 individuals were sampled from fish markets along the western coast of Galicia (NW Spain), between November 2009 and October 2010. Histological examination of the gonads revealed an asynchronous development of secondary growth follicles. Testicular tissue was of lobular type. The reproductive season extended from January to April for females and from January to May for males, with a peak of reproductive activity in February for both sexes. The hepatosomatic index was related to the reproductive cycle, with a mean maximum value during the developing reproductive phase. Length at 50% maturity was significantly different between females (47.1 cm) and males (36.1 cm).

A one-year study of the reproductive biology of a population of Diopatra marocensis at the Villaviciosa estuary, northern Spain, was undertaken with emphasis on brooding behaviour, larval development and gametogenesis. Field observations together with a histological study of monthly collected individuals revealed that the population was iteroparous, reproducing annually during a short breeding season extending from March to June. The study demonstrated that all individuals of the population at Villaviciosa estuary were producing at the same time eggs and sperm providing for the first time evidence for the occurrence of simultaneous hermaphroditism in D. marocensis. Mature sperm was of the ent-aquasperm type and was stored in modified nephridial chambers in brooding individuals. In the latter, eggs in advanced cleavage phases were also observed inside the coelom suggesting that fertilization was internal. Eggs in late vitellogenesis presented micronucleoli in the periphery of the nucleus, a phenomenon reported previously for few polychaete species. Pure males and females were never found. It is here suggested that in D. marocensis population size may influence sex allocation and that under conditions of low population densities simultaneous hermaphrodites may be favoured. The study of the larval development confirmed the direct development reported previously for populations of Morocco and Portugal. Further results suggest consumption of nurse eggs and adelphophagy by developing larvae.

In amphibians, the components of the jelly coats that surround the oocytes at the time of fertilization and coordinate gamete interaction are secreted by the oviduct. We analysed the histological variations in the mucosa of the oviductal pars convoluta (PC) of Rhinella arenarum during the reproductive cycle and its relationship with secretion. During the preovulatory period, the mucosa reaches a high degree of morphological and functional development, with a large number of epithelial (ESC) and glandular secretory cells (GSC) loaded with contents that are secreted into the oviductal lumen. During the ovulatory period, the secretory cells (SC) of both layers present maximum secretory activity through apocrinia and merocrinia. While the ESC located at the tips of the folds release their content directly in contact with the oocytes, the GSC secrete material from the bottom of the epithelial folds that, by interaction with the secretion of the ESC in the lateral faces, form a product with a certain degree of organization. Secretion is a continuous process with formation of coats of increasing complexity from the intermediate proximal zone (IPZ) to the pars convoluta (pc) itself, and the passage of the oocyte is a requisite for the organization of the jelly coats around the gamete.

During the early postovulatory period, although there is a marked decrease in the number and volume of the SC, the ESC still release material into the oviductal lumen. In the late postovulatory period the morphological characteristics of the PC begin to recovery although there is no evidence of secretion.

Hypermastus tokunagai is a eulimid gastropod infecting the sand dollar Scaphechinus mirabilis. The eulimid is easily detached from the host and thus regarded as a temporary parasite. In this study, the growth and reproductive cycle of H. tokunagai were investigated using specimens collected from S. mirabilis in the western Seto Inland Sea, Japan. Newly recruited individuals of H. tokunagai appeared in early autumn and grew rapidly, while growth was retarded from mid-autumn to winter months. A second rapid growth occurred the following summer. Based on the growth pattern, the life span of H. tokunagai was estimated to be more than 20 months. This longer life span compared to other eulimids could be due to the accessibility and population stability of its host S. mirabilis. Maturation of H. tokunagai occurred within a short period in the summer, and was synchronized with the second growth phase. Hypermastus tokunagai showed size dimorphism between sexes and an investigation on change in shell shape with growth revealed that this characteristic can be attributed to the female's acquisition of a larger shell within a short time during its maturation period.

In the current study, commercially valuable penaeid shrimp, Melicertus kerathurus, were attained approximately monthly in the Izmir Bay, southern Aegean Sea from May 2004 to April 2005. For each specimen, we measured body length, body weight and ovarian weight, and calculated gonadosomatic indices (GSI). GSI values results pointed out that the GSI in Melicertus kerathurus increased during vitellogenesis (2.03 ± 0.24%) but sharply decreased after spawning (0.53 ± 0.35%) to reach levels similar to those in immature females. We also examined oogenesis in Melicertus kerathurus by histological observation of the ovary to determine reproductive cycle for future domestication. The observation on the gonads leads us to conclude that there are five stages of development for the females: (I) previtellogenic; (II) early vitellogenic; (III) late vitellogenic; (IV) mature; and (V) spent. Histological characteristics showed that the best time to capture adult shrimps for breeding purposes was between the months of April and June. The numbers of each oocyte type that were present were also counted, measured, and used to evaluate the following traits: total oocyte number; mean oocytes diameter; and maximum oocyte diameter. Oocyte diameter was significantly different at all stages (P < 0.05) and the largest diameter was observed as 163.92 ± 4.51µm at stage IV.

The common whelk Buccinum undatum (Neogastropoda, Buccinidae) is widespread along the north Atlantic coasts of France. In west Cotentin (Normandy), an important local fishery exists that depends exclusively on this marine resource and represents about 90% of French whelk production. Despite successive restrictive measures, fishing yields have decreased since 2000. Shell length frequency distributions of Buccinum undatum caught in west Cotentin were studied in 2005 (N = 2910), in 2007 (N = 2032) and in 2009 (N = 4145) ranging from 7 to 85 mm. In order to preserve this fishery and to characterise the whelk stock at this site, the reproductive biology of this species was studied in relation to age, sex and size, for whelks of commercial size (45 to 61 mm) over the complete annual cycle in 2008. Age was determined by reading the number of operculum striae: animals between 45 and 59 mm had 2 to 4 striae. Four reproductive stages were defined for males and females on the basis of histological analysis. The time course of reproductive events was described according to size and sex: the highest percentages of ripe stages were found in October for both sexes. Spawning events occurred between October and December. The shell length that corresponded to 50% of animals having mature gonads (49 mm and 52 mm for males and females, respectively, corresponding to 3 and 4 years old animals) exceeded the minimal landing size (45 mm). Fifty percent maturity was reached for males in their third year and for females in their fourth year. Reproductive investment was evaluated by quantitative analysis of the gonadal thickness or surface and was found to be proportional to shell size. We found that less than 20% of females under 49 mm in length were sexually mature and that these produced only a few eggs. This information, collected in a major fishing area, should assist fishery management decisions.

The spiny dogfish Squalus acanthias is widely distributed in Atlanto-Mediterranean regions, being captured off the Languedocian coast (southern France, northern Mediterranean), despite a decline of landings. The male and female sexually matured between 635–700 mm and 860–880 mm total length (TL), respectively. The largest male and female were 800 mm and 1110 mm TL, respectively and weighed 2220 g and 8900 g, respectively. There was a significant relationship for total mass versus TL, and liver mass versus TL between males and females. The diameter of the largest yolky oocytes ranged between 43 and 47 mm (mean 45.08 ± 0.98), while the mass ranged between 29.5 and 37.4 g (mean 31.79 ± 2.20). Near- term embryos ranged from 245 to 271 mm TL (mean: 258.85 ± 7.28) and weighed from 47.5 to 55.9 g (mean 53.35 ± 2.26). Ovarian fecundity ranged from 6 to 15 (mean = 10.38 ± 2.66). Uterine fecundity or litter size ranged from 4 to 12 (mean = 8.15 ± 2.07). Both fecundities showed a positive relationship with TL of females. A chemical balance of development based on mean dry masses of yolky oocytes and near-term embryos was 0.87 and suggested that S. acanthias is a pure lecithotrophic species. Hepatosomatic index (HSI) and gonadosomatic index (GSI) significantly increased with size in both males and females. HSI reached the highest values in both sub-adult and adult specimens, reflecting the role of the liver in the gonadal production as well as in buoyancy, while in the GSI the highest values were observed in pregnant females. Vitellogenesis proceeds in parallel with embryonic development. Near-term females were captured in different months of the year while a short period of resting could not be excluded between parturition and the beginning of a new pregnancy, so it appears difficult to delineate the length of gestation. However, a reproductive cycle with a wide range from 18 to 24 months remains a suitable hypothesis.

We examined the density and reproductive characteristics of the Israeli population of the cryptic species complex Dendropoma petraeum—a Mediterranean endemic reef-building gastropod. The population is gonochoristic, with a peak of gonad activity from October–November to May–June. We present here for the first time histological evidence of its reproductive cycles, hermaphroditism and gonadal parasitic infestation. The characteristics studied (gonad activity period, number of egg capsules per female, capsule size and number of eggs/embryos per capsule) were markedly different from those reported for the D. petraeum-complex population in south-east Spain. Our findings on the population's reproductive characteristics provide new information on the differences between the Mediterranean populations of D. petraeum-complex.

The reproductive biology of Psammobatis lentiginosa was studied in San Matías Gulf (Patagonia, south-west Atlantic). A total of 1033 skates was analysed, total length ranged from 17 to 52 cm for females and from 13 to 55 cm for males. Total length–total weights relationships differed between sexes, with TW = 0.005 × TL3.02 for females and TW = 0.005 × TL2.97 for males. The overall sex-ratio was 1:1. In females, the L50% was 41.06 cm, in males the L50% was 41.38 cm. The mean number of yolked oocytes per skate was 4.22 (±2.41). The mean number of yolked oocytes and the length of the female were linearly related. The diameter maximum of yolked oocytes was 24 mm. The species exhibited a continuous reproductive cycle throughout the year, with a peak of egg-case production during autumn that was synchronous with maximum values of the epididymis and uterus indices. This is the first record of a reproductive aggregation for P. lentiginosa in San Matías Gulf, North Patagonia. This finding together with its continuous presence around the year, suggest that this area is the main distribution area of P. lentiginosa in the south-west Atlantic.

The wide-eyed flounder Bothus podas podas is a small fish that belongs to the Bothidae family. This species is a demersal fish inhabiting sandy and muddy bottoms where it lives buried in the sand. In the Gulf of Gabès (Tunisia), B. podas podas is an uncommon fish caught in small quantities by trawlers, between depths of 20 and 50 m. There are very few complete studies of the biology of this fish in the Mediterranean Sea. Even in Tunisia, the biology of B. podas podas is unknown. In addition, it has been noticed that during the last few years, despite having weak commercial value, this fish has attracted the fishermen's attention of the region after the observed reduction in the flat fish stocks, particularly the Egyptian sole Solea aegyptiaca. The aim of this work was to study the reproduction of B. podas podas and determine the sex-ratio, the sexual cycle, the spawning period and the first sexual maturity. The data for this work was collected during the period of May 2004 until September 2005. In general, this study shows that the proportion of sexes is in favour of females and permits us to analyse the sex-ratio variations according to the size and age of the fish. It also seems that males grow faster than females. The monthly following of the gonad somatic index (GSI), the liver somatic index (LSI) and the condition factor (K) enabled us to determine that the period of maturation occurs from May to August, to define the spawning period from August to November and to deduce that B. podas podas uses the lipid reserves accumulated in the liver to develop its gonads. Concerning the first sexual maturity it was noted that the main size related to 25%, 50% and 75% of matured individuals were respectively for males: 19.68 cm, 21 cm and 22.34 cm and for females: 18.87 cm, 20.4 cm and 21.93 cm. The coefficients of the logistic function were for males: a = 0.827, b = 17.38 and for females: a = 0.718, b = 14.65.

At Burgers' Ocean 7 male and 3 female blue spotted stingrays, Dasyatis kuhlii were born over a period of 4.5 years. This paper describes the experiences of the captive breeding results of this species. The first two young died within 2 days of birth. One of them had an internal yolk sac, which may feed the young in the first few days. The other eight animals started to feed after 4 to 9 days on a variety of food types. Birth size of the young increased with increasing age of the parents. Mating occurred directly after parturition, so no seasonality could be defined. Gestation length ranged between 138 and 169 days, with a mean of 144.9±9.0 days (N = 11). Litter size was one, possibly caused by only one active ovarium. Sexual maturity of the two parent animals is approximately 3.5 years. The average feeding rations for the adults ranged between 10.1% BW week−1 (131 kcal kg BW−1 week−1) and 11.3% BW week−1 (172 kcal kg BW−1 week−1), with a feeding frequency of 4 times per week. The relationship between body weight (BW) and wingspan (WS) is given as BW = 3.6 × 10−5* WS2.940 (R2 = 0.9645; N = 45).

The banded guitarfish, Zapteryx exasperata, is a common species in the artisanal elasmobranch fisheries in the Gulf of California. Fishery-derived specimens were examined to determine critical aspects of the reproductive biology of this poorly known group of rays. Two functional testes and ovaries were found in males and females respectively. Median size at maturity (L50%) for males was 64 cm total length (TL) and for females 69 cm TL. Average length of gravid females was 78.8±3.8 cm TL. Histological analysis showed no evidence of sperm storage in the oviducal gland. Gestation was estimated to occur over a five to six month period (February–July) and was concurrent with vitellogenesis. Mean uterine fecundity was estimated as 7 (range 2–13, SD. = 3). The sex-ratio of embryos was 1:1. The reproductive cycle for Z. exasperata from the Gulf of California was estimated to last one year with parturition, ovulation and copulation occurring during the summer months. Differences found in the reproductive cycle of Z. exasperata between the Gulf of California and the west coast of Baja California could have implications in the future management plans for this fishery in the Gulf of California.

This study aimed to assess the influence of growth and reproductive cycle on the meat yield and proximate composition of the banded murex (Hexaplex trunculus) from the Ria Formosa lagoon (Algarve coast, southern Portugal). Samples of the edible portion (all soft-body tissues) were analysed monthly during one year. The average meat yield was 37.9±4.6%, with females containing more edible content (39.1±4.7%) than males (36.8±4.2%). The proximate composition comprised 70.7±1.4% moisture, 20.1±1.2% protein, 1.6±0.3% fat, 3.0±0.3% ash, and 4.6±1.2% carbohydrate, corresponding to an energetic value of 119.2±7.5 kcal/100 g wet weight. The meat yield was influenced by specimen size, increasing significantly during growth. Both meat yield and proximate composition presented seasonal fluctuations related to the reproductive cycle, which coincided mainly with the periods of maturation and spawning of this species in the Ria Formosa. Finally, H. trunculus meat yield and proximate composition were compared with similar information available for other marine gastropods.

The reproductive cycle of Zygochlamys patagonica was studied from October 1999 to February 2001 in a bed located in the south-western Atlantic (Reclutas bed 39°24′ S–55°56′W). Scallops were collected monthly and the sexual maturity stages were determined histologically (N = 508). Sex-ratio was 1:1 (t-test P > 0.05). The size of first sexual maturity was estimated from males of an average of 36.63 mm and females of 36.31 mm of shell height. The relative gonadal condition index (RGCI) showed an annual cycle, with higher values during winter–spring and lower values during summer–autumn; an inverse relationship for the relative muscle condition index (RMCI) was observed with maximum values in early summer. Thus, a reallocation of energy from soma to gonad appears to be inevitable to meet energy demand of gonad development. Seven histological stages of sexual maturity were established for both sexes: (1) immature; (2) early maturity; (3) advanced maturity,;(4) ripe; (5) spawning; (6) spent; and (7) recovery. Individuals in early and advanced maturity were found throughout the year; however, they were found more frequently between June and September. Spawning began in October (early spring) and extended through March (late summer–early autumn) coexisting with early and advanced maturity stages supported by the annual variation of the RGCI and the food availability into the system.