Female crabs enter a stage of rapid ovarian development after mating, and cholesterol is a substrate for steroid hormone synthesis. Therefore, in this experiment, an 8-week feeding trial was conducted to investigate the effects of mating treatments (mated crab and unmated crab) and three dietary cholesterol levels (0·09 %, 0·79 % and 1·40 %) on ovarian development, cholesterol metabolism and steroid hormones metabolism of adult female swimming crab (Portunus trituberculatus). The results indicated that crabs fed the diet with 0·79 % cholesterol significantly increased gonadosomatic index (GSI) and vitellogenin (VTG) content than other treatments in the same mating status. Moreover, mated crabs had markedly increased GSI and VTG content in the ovary and hepatopancreas than unmated crabs. The histological observation found that exogenous vitellogenic oocytes appeared in the mated crabs, while previtellogenic oocytes and endogenous vitellogenic oocytes were the primary oocytes in unmated crabs. The transmission electron microscopy analysis showed that when fed diet with 0·79 % cholesterol, the unmated crabs contained more rough endoplasmic reticulum and mated crabs had higher yolk content than other treatments. Furthermore, mating treatment and dietary 0·79 % cholesterol level both promoted cholesterol deposition by up-regulation of the mRNA and protein expression levels of class B scavenger receptors 1 (Srb1), while stimulating the secretion of steroid hormones by up-regulation of the mRNA and protein expression of steroidogenic acute regulatory protein (Star). Overall, the present results indicated that mating behaviour plays a leading role in promoting ovarian development, and dietary 0·79 % cholesterol level can further promote ovarian development after mating.

An organism's maximum gonad investment (MGI) typically indicates its reproductive season and is often measured by the peak of the gonadosomatic index. Since external sexual dimorphism is often not evident, intrinsic sex differences remain unstudied. We analysed the reproductive seasonality of each sex of the broadcast-spawning sea cucumber Holothuria (Halodeima) inornata in two populations (Caleta de Campos, Michoacán ‘CC’ and Puerto Madero, Chiapas ‘PM’) in the southern coast of the Mexican Pacific by examining: intensity and duration of MGI, frequency of each gonadal developmental stage (GDS) through time, sexual asymmetry in GSI, sexual asymmetry in GDS, and adult sex ratio. We observed a trade-off between the intensity (%) and duration (months) of each sex's MGI: as intensity decreases, duration increases and conversely. The frequency of ripe and spawning stages was consistently higher in females than males. Sexual asymmetry in GSI was slightly female-biased in the PM population, but male-biased in the CC population. Sexual asymmetry in GDS showed a more recurrent sexual equality at PM than at CC. The adult sex ratio of each population did not differ significantly from unity, but showed a near-significant trend for male bias in the CC. Although H. inornata exhibited different MGI responses between males and females and more markedly in CC than in PM, it also showed a synchronized relation between its mass investment (GSI) and physiological investment (GDS), possibly reflecting an optimum reproductive strategy. Lastly, changes in GSI were not underpinned by changes in local temperature, but rather by regional temperature.

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.

Parasite distribution among hosts is a fundamental aspect of host–parasite interactions. Aggregated parasite distributions within and across host species are commonly reported and potentially influenced by many factors, whether host or parasite specific, or related to host–parasite encounter and compatibility. Yet, the respective role of each in observed parasite distributions are often unclear. Here, we documented the distribution of the acanthocephalan parasite Pomphorhynchus laevis sensu lato (s.l.) in two replicate fish host populations. Aggregated distributions were observed in both populations, within and across fish host species. We found a positive abundance–prevalence relationship across fish species, suggesting that resource availability (fish host biomass density) was the main driver of P. laevis s.l. distribution. This was supported by further positive associations between mean parasite load and fish biomass density. We found little evidence for intensity-dependent regulation within host (i.e. intra-host competition among co-infecting parasites). Furthermore, P. laevis s.l. infection had no detectable effect on fish condition indices, except on the body condition of female barbel (Barbus barbus). Therefore, P. laevis s.l. tended to accumulate with size/age within fish species, and with fish biomass density among fish species, with apparently negligible limitations due to intra-host intensity-dependent regulation of parasite, or to parasite-induced morbidity in fish. The relative availability of final hosts for trophic transmission thus appears to be the main driver of P. laevis s.l. distribution among fish.

A survey of Antarctic toothfish (Dissostichus mawsoni) was conducted in the northern Ross Sea region during the winter of 2016 to document the timing and location of spawning activity, to collect biological information about reproductive status during the spawning season and to look for temporal signals in biological data from D. mawsoni that may indicate a spawning migration of mature toothfish from the continental slope region to the northern Ross Sea region. The 58 day survey showed that spawning of D. mawsoni began on some seamounts by early July. No changes were detected between winter and summer in length, age, sex ratio or condition factor distributions for D. mawsoni in the northern Ross Sea as hypothesized following a spawning migration from the slope to the northern Ross Sea region. These results suggest that the distribution of D. mawsoni in the Ross Sea is mainly accomplished through ontogenetic migration and not annual return spawning migrations.

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.

Solea aegyptiaca (Chabanaud, 1927) is one of the most common Soleid species in southern Tunisian waters. This study provides the first detailed information on the reproduction biology of S. aegyptiaca in these areas. Samples of S. aegyptiaca were collected by trawl from the Gulf of Gabes (Tunisia) between April 2013 and March 2015. A total of 1638 specimens were examined, ranging from 9.7 to 30.7 cm total length. The sex ratio was in favour of males in smaller size classes and females in larger size classes. The macroscopic analysis of the gonads and the progression of the monthly values of the gonadosomatic index (GSI) indicated that the reproductive season extended from October to February, with GSI peaking in November and December for males and females respectively, and that spawning occurs once a year from November to February. The utilization of lipid reserves, stored predominantly in the liver as well as in muscles, was depicted. The estimated average length at first maturity was 22.31 ± 0.41 cm for males and 23.19 ± 0.184 cm for females. Total fecundity of mature females ranged from 14,160–62,700 eggs per fish, showing a significant increase with size, with an average of 33,020 ± 5239 eggs per fish.

Reproductive cycles were studied in seven natural populations of the intertidal bivalve Perumytilus purpuratus, distributed in a latitudinal gradient of ~2400 km along the Chilean Pacific coast (20–40°S). The results, both qualitative (gametogenic stages) and quantitative (GSI and GVF), over a period of 24 months, showed that these populations presented asynchrony in the reproductive cycle. Semi-annual cycles in Iquique (20°S), Antofagasta (23°S) and Montemar (32°S), and annual cycles in Caleta Bolfin (23°S), Taltal (25°S), Tumbes (36°S) and Pucatrihue (40°S) (2010–2012) were found. The results indicate that latitude does not have an effect on the development stage, but it does on the spawning date. However, there is a relationship between the reproductive cycles and temperature fluctuations. In addition, there was a significant negative linear correlation between gonadosomatic index and sea surface temperature in the populations studied. The decrease in temperature reduces the rate of development stages and, therefore, increases the reproductive cycles from semi-annual to annual, as evidenced in bivalve samples from Taltal, along a semi-decadal period (2007–2012). From these results, we discuss the likely biological and ecosystem consequences in connection to the effects of climate change in the South Pacific.

When and where marine eels spawn is poorly known even though species such as those of the family Congridae, Muraenidae and Ophichthidae can be caught in continental shelf habitats. The congrid genus Ariosoma includes small continental shelf eel species whose life histories are not yet known. Mature male and female eels of Ariosoma meeki were observed and captured on 17 August 2009 at the surface at night in the western side of the Kuroshio Current in the East China Sea close to new moon, while they were swimming slowly at the surface and exhibiting apparent reproduction-related behaviour. One male and one sex-unidentified eel (seemingly a male based on body shape) were observed to be chasing one larger female with their heads located near her urogenital pore area. The gonads of the female (540 mm) and the male (410 mm) that were caught by a long-handled dip net were in reproductive condition, because some eggs or seminal fluid were released during handling of the two specimens and high gonad-somatic index (GSI) values of 53 in the female and 20 in the male were recorded. This is one of the few cases in which fully ripe reproductive-condition marine eels have been observed or collected and it provides rare information about the spawning location and timing of this eel species.

Thunnus alalunga is an important commercial tuna species widely distributed in the three major oceans and the Mediterranean Sea. The Mediterranean population is currently classified as a data-poor stock and little is known about its basic life history parameters. This study provides the first detailed information on some aspects of the reproductive biology of T. alalunga from the western Mediterranean Sea. A total of 16 104 specimens were measured between 2005 and 2012. The overall sex ratio of females to males was 1.1:1, although the ratio was female biased in fish <70 cm fork length (LF) and male biased in those >75 cm LF. Histological analysis of the ovaries (N = 587) and the monthly variation of the gonadosomatic index for both sexes showed that spawning occurred from June to August, which is a much shorter period than the 7 months reported for T. alalunga in tropical oceanic waters. Thunnus alalunga caught during June and July are capable of spawning daily. The gonadosomatic index values for T. alalunga from the western Mediterranean were up to eight times higher than those of T. alalunga from other oceans. Histological examination of the ovaries showed that the minimum length at sexual maturity of females was 56 cm LF, which is considerably smaller than those estimated for other stocks.

In a study of the age and growth of Platycephalus indicus, a total of 1106 fish were collected from May 2011 to March 2012 in the coastal waters of Iran, Persian Gulf. The ages of 279 specimens were determined by sectioned otoliths. The ages of the females were estimated to be between 0+ to 7+ , while the ages of the males were from 0+ to 4+. The von Bertalanffy growth curve was well suited to the age/total length data of males and females as follows: Lt = 43.40{1–exp[−0.45(t + 0.328)]} for males, and Lt = 63 {1–exp[−0.50(t + 0.30)]} for females. linf = 43.40, k = 0.45, t0 = −0.328 for females and linf = 63, k = 0.50, t0 = −0.30 for males. The estimated values of natural mortality (M) were M = 0.886 yr−1 for females and 0.736 yr−1 for males, and the estimated Z values were 1.43 yr−1 for females and 1.62 yr−1 for males. The mean value of the gonadosomatic index for males and females was 0.82 ± 0.25 and 2.48 ± 0.59, respectively, in each year. The mean values of the hepatosomatic index (HSI) were 0.89 ± 0.20 for males and 1.28 ± 0.16 for females. The highest HSI values for this location were observed in January, and the lowest were in April.

The black goby Gobius niger (Linnaeus, 1758) (Gobiidae) is one of the most common gobies in southern Tunisian waters. This study provides the first detailed information on the reproductive biology of the G. niger in these areas. Samples of G. niger were collected by trawl from the Gulf of Gabès (Tunisia) between February 2009 and January 2010. A total of 1055 specimens were examined, ranging from 6.4 to 15.7 cm total length. The sex-ratio was in favour of males, especially in larger size-classes. The macroscopic analysis of the gonads and the progression of the monthly values of the gonadosomatic index (GSI) indicated that the reproductive season extended from March to June, with GSI peaking in May, and that spawning occurred from April to June. The utilization of lipid reserves, stored predominantly in the liver as well as in muscles, was important during the reproduction season. Monthly changes of the seminal vesicle somatic index showed that during the pre-spawning period they had a proliferation phase, followed by a regressive phase during the post-spawning period. Total fecundity of mature females ranged from 4280 to 14000 eggs per fish, showing a significant increase with size, with an average of 8522 ± 689 eggs per fish. The total length at 50% maturity was 10.13 ± 0.3 cm and 9.69 ± 0.18 cm for males and females, respectively.

Sampling of the fish community was carried out for 20 years in the Mirgenbach reservoir, in North-Eastern France. The prevalence and the mean intensity of Ligula intestinalis (Cestoda) were analysed in roach (Rutilus rutilus) and silver bream (Blicca bjoerkna) populations, the main two infected species. The aim of this study was to investigate the host switch from roach to silver bream and the consequences of L. intestinalis infestation in silver bream, which is an unusual host for this parasite as Ligula parasitism in silver bream appears to be rare. We analysed in detail the relationships between parasitism index (PI), gonadosomatic index (GSI), perivisceral fat abundance (PFA) and condition index (CI) in the silver bream population. In 1998, prevalence of L. intestinalis highlighted a clear host switch from roach to silver bream. In the silver bream population, young fish were the most severely infected and the impact of plerocercoids appeared to be different depending on the host sex. In male silver bream, plerocercoids drew energy from fat reserves even if GSI was also slightly impacted. On the contrary, in females energy was diverted from gonad maturation rather than from perivisceral fat reserves. No significant difference was observed in terms of CI in either sex.

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 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.

Portunus pelagicus a commercially important crab species found in Chilika lagoon constitutes about 20% of the total crab production. The carapace width (CW) ranges from 4.5–10.5 cm in both the sexes during the study period. The maximum abundance of male was at 6.6 to 7.5 cm CW whereas the females predominate from 6.6 to 9.5 cm CW. The relationship between carapace length (CL) and CW is linear in both sexes which indicates isometric growth. However, the relationship between CL, CW with total body weight (TW) is exponential. The food habit from gut content analysis shows that the species is highly carnivorous and the main food items include prawn carapace and appendages (27.58%), molluscan remaining (21.55%), fish bone (7.75%), seagrass (1.72%), unidentified materials (4.31%) and the mixed food (37.06%). The feeding index was found highest (80.95%) in February whereas it is lowest (60.9%) in June. The mature females are observed from May to July with a peak in July in the lagoon. The highest gonadosomatic index is found in July with an average CW of 10.5 cm. No berried females are found in the study period, which indicates that it did not spawn inside the lagoon and migrates to the sea during the rainy season.

The present study describes the reproductive biology, population structure and life history traits of the abundant intertidal crab Xantho poressa. Between March 2007 and April 2008, a total of 1918 individuals were collected in Corrales de Rota (south-western Spain), a human-modified intertidal habitat characterized by an artificial high complexity. Suitable refuges for crabs (cobbles and boulders) are very abundant in this area and density (maximum of 50 ind*m−2) was directly related with the area covered by these stones. In spring and summer, size–frequency distributions showed a polymodal pattern with seasonal variations related to the incorporation of juveniles to the adult population. Newly settled juveniles were not found in the Corrales suggesting an ontogenetic migration from a distant recruitment habitat. The annual reproductive cycle was seasonal and successive peaks in the abundance of ovigerous females were observed in late spring and summer. Females probably produced multiple broods during a long intermoult period. The gonadosomatic index had a cyclic pattern of variation with peaks two weeks prior to those of ovigerous females; it was lower during the non-reproductive season. The hepatosomatic index was high during spring, decreased during summer and increased gradually at the end of the reproductive season. There was a monthly cycle of larval release resulting from a combination of a cyclic and synchronic ovarian maturity, oviposition and incubation; hatching took place during neap tides when the moon was at last quarter. The adaptive significance of the rhythmic reproduction and hatching observed may not be explained by the predator avoidance hypotheses. The overall sex-ratio did not differ from 1:1 but one male and several females coexist under a stone, indicating a female biased operative sex-ratio. The combination of a complex habitat, its use, and a strong sexual dimorphism suggest a refuge–defence polygenic mating system. The survival and fitness of X. poressa in the Corrales de Rota are probably enhanced by the availability of shelter, a consequence of a highly complex habitat, and probably, of human activity.

The impact of toxic outbreaks of Gymnodinium catenatum, producer of paralytic shellfish poisoning toxins (PSP toxins) and Pseudonitzschia spp., producer of amnesic shellfish poisoning toxins (ASP toxins), was studied throughout the culture cycle of the king scallop Pecten maximus (length from 40 to 100 mm). Toxin concentration, in plankton and in the digestive gland of the scallops, other variables that describe the state of the cultured scallops (mortality, growth, length/weight ratio, gonadosomatic index) and the main environmental conditions (temperature and in vivo fluorescence) were determined from December 2001 to April 2003. Temperature ranged from 14 °C during the winter to 22 °C at the end of July. In vivo fluorescence ranged from not detectable to 25 relative units, with a maximum also recorded at the end of July. ASP toxin levels, in both plankton and organisms, were high during the first half of the sampling period (maximum 450 ng domoic acid L−1, in plankton, and 175 µg·g−1 of scallop digestive gland) when the scallops were juvenile. PSP toxins attained larger concentrations in the second half of the sampling period (maximum of 1.8 nmol L−1 in plankton and 550 nmol g−1 of digestive gland, of gonyautoxins after hydrolysis). Several mortality events took place during the period studied, but none of them coincided neither with an ASP or PSP outbreak nor with long exposure of the scallops to these toxins. One of the recorded mortalities occurred simultaneously with a high concentration of PSP in the scallops, but also with an important spawning. Additionally, it was not coincidental with the bloom of toxic plankton, thus, post-spawning stress seemed to be the main responsible for the mortality. No appreciable effect of ASP or PSP toxinson growth or reproductive state of the cultured scallops was found. Therefore, neither ASP nor PSP toxins appeared to represent a direct threat to the culture of Pecten maximus in that case.

Gonad maturation in Antarctic notothenioid fish is a biennial process although spawning is likely to take place annually. However, part of the populations of Champsocephalus gunnari in the Atlantic Ocean sector do not spawn each year. Gonadosomatic index (GSI) of females is 15–40% at spawning. Apart from a few nototheniid species of the GSI of males is much less and typically only 15–20% of that of females. Length at first spawning may be from 55% of Lmax onwards, but in many species it is not attained until 70–80% of the maximum length. The only exception is Champsocephalus gunnari at South Georgia which may begin spawning at about 40% of Lmax. Most species of the Seasonal Pack-ice Zone are autumn/winter spawners, whereas in the High-Antarctic Zone more species spawn in summer and autumn. Spawning time is remarkably constant among populations of some species, in others a latitudinal shift in spawning time is apparent. Fecundity is commonly positively correlated with fish length and weight. It exceeds 100 000 eggs only in a few nototheniid species and is commonly in the order of 1000 to 15–20 000 eggs. Ova diameter varies from 0.8 to 5.0 mm. Egg size distribution among fishes of the Seasonal Pack-ice Zone is bimodal. There is a general trend in nototheniids of increasing egg size and decreasing relative fecundity towards higher latitudes. Incubation time may be up to five months. Eggs of most species are probably left unattended for the long incubation period. Nest guarding has been observed in three species but may be more common in particular among the artedidraconids. A number of reproductive strategies associated with nest guarding, egg size and the duration of the pelagic phase have been identified.

This study was based on wild-caught blacklip abalone Haliotis rubra L., from Port Fairy waters, south eastern Australia (142°15'E; 38°21'S), from July 1998 to November 1999, and was initiated to evaluate the spawning season and other aspects of its reproductive biology. The shell length and body weight of female and male abalone sampled ranged from 12.0 to 18.6 and 12 to 15 cm, and 137 to 529 and 148 to 585 g, respectively. The sex ratio did not vary significantly from 1:1 through the year. The gonadosomatic index (GSI) ranged from 3.0% to 8.4% in males, and 2.5% to 14.1% for females, and the highest GSI as well as the highest proportion of mature animals were recorded from September to October. During these months the hepatosomatic index (HSI) was low, and an inverse correlation between GSI and HSI (P < 0.05) was evident. Fecundity of blacklip abalone ranged from 1.09 to 7.5 million eggs for females of 12–14.5 cm in length, and 115–487 g in total body weight, respectively. The lipid content of the female gonad increased significantly from about July to November, and an opposite trend was observed for lipid content of the digestive gland. Seasonal changes in the protein and ash contents of the gonad and/or the digestive gland were not always significant.