Gonad Index Research Articles

Moderately elevated temperatures increase macroalgal food consumption in two sea urchin species from coastal waters of Madeira

Rising sea surface temperatures affect the feeding behaviour and reproductive success of many coastal benthic invertebrates. This experimental study investigated the effects of ocean warming on macroalgal food consumption rates in the sea urchins Arbacia lixula and Paracentrotus lividus from Madeira Island to assess how the feeding pressure they exert may change under warmer ocean conditions. Additionally, in A. lixula, the relationship between temperature and the gonad index was examined to estimate potential future reproductive output. Over the course of 25 days, 180 individuals of each species were exposed to temperatures between 22 °C and 31 °C. After 20 days, consumption rates were assessed in 48-h feeding trials. Gonad indices of A. lixula were determined on the last day of the experiment. In the thermal range investigated, both traits were found to be unimodal functions of temperature. In addition to temperature, consumption rates in both species and the gonad indices in A. lixula were influenced by body size, while feeding in A. lixula also varied between sexes. Maximum food consumption rates (A. lixula and P. lividus) as well as maximum gonad indices (only A. lixula) were observed between 25 °C and 26 °C. These values are at the upper end of the temperature range that currently prevails around Madeira, and may become average summer temperatures by the year 2100. Consequently, both sea urchin species may thrive during future warm summers and may enhance their top-down control on local macroalgal populations.

A depth-dependent assessment of annual variability in gonad index, reproductive cycle (gametogenesis) and roe quality of the green sea urchin (Strongylocentrotus droebachiensis) in Breidafjördur, west Iceland

This pilot study aimed to assess whether depth had an impact on the sexual development and quality of green sea urchin (Strongylocentrotus droebachiensis) gonads, and whether market quality urchins could be found at greater depths than usually fished in Breiðafjörður, west Iceland. Green sea urchins were collected monthly at 32 and 60 m depth sites from September 2016 to August 2017. Development and spawning time at both sites were determined by examining monthly changes in gonad index (GI), gametogenesis (nutritive vs. gamete cell development) and sexual stage progression. Gamete development and sexual staging suggested that depth may not significantly impact sexual development, gametogenesis, or the onset of spawning at the study sites. While minor differences in gametogenesis between sexes were observed at both sites, statistical differences were only found in May at 60 m depth. Sex ratios were nearly 1:1 overall at both depth sites, with no observed incidences of hermaphroditism. Market quality urchins, in terms of GI and color, were found at both sites, though results suggested that increasing depth may have a negative impact on quality. Gonad colors met or exceeded minimum market standards from August to March at both depths, with low incidence of unacceptable coloration, though results suggested that increasing depth had a negative impact on color. Additional research regarding these factors is vital for sustainable utilization.

The Effect and Mechanism of Hyperin on Ovarian Reserve of Tripterygium Glycosides-Induced POI Mice

To investigate the effect and mechanism of hyperin on the improvement of ovarian reserve of tripterygium glycosides (TG)-induced primary ovarian insufficiency (POI) in mice. Adult female BALB/c mice were used as research subjects and were randomly assigned to the control group, POI model group and hyperin treatment group, with 40 mice in each group. TG was given at 40 mg/kg twice a day by gavage for 2 weeks to create the POI mouse model. Mice in the hyperin treatment group were given hyperin at 75 mg/(kg·d) by gavage for 4 weeks after the model was established. The body mass of the mice was weighed and the gonadal index was calculated. Ovarian histological changes were observed by HE staining, and the number of follicles at all levels was calculated. Serum estradiol (E 2), follicle-stimulating hormone (FSH), anti-mullerian hormone (AMH), superoxide dismutase (SOD) and catalase (CAT) were assessed with ELISA. The mRNA and protein levels of nuclear factor (erythroid-derived 2)-related factor 2 (Nrf-2), heme oxygenase-1 (HO-1), Caspase3, Bcl-2 and Bax in ovarian granulosa cells were measured by RT-qPCR and Western blot. The protein levels of phosphorylated phosphatidylinositol 3-hydroxy kinase (p-PI3K) and phosphorylated protein kinase B (p-Akt) were measured by Western blot. The reactive oxygen species (ROS) levels in granulosa cells were determined by H2DCFDA. The apoptosis of granulosa cells was examined by TUNEL assay. Compared with mice in the POI model group, the body mass and gonadal index of hyperin-treated mice increased (all P<0.05). The pathological damage of the ovary decreased, and the number of follicles at all levels and corpora lutea increased (all P<0.05). Serum E 2, AMH, SOD and CAT levels increased, and FSH level decreased (all P<0.05). At the molecular level, the expression of Nrf-2, HO-1, p-PI3K, p-Akt and Bcl-2 in ovarian granulosa cells increased, while the expression of Caspase3 and Bax decreased (all P<0.05). ROS level decreased ( P<0.05). TUNEL assay showed reduced apoptosis of granulosa cells ( P<0.05). Hyperin improved ovarian reserve in TG-induced POI mice through Nrf-2/HO-1antioxidant stress response and the anti-apoptotic effect of PI3K/Akt pathways.

Variation in purple sea urchin (Strongylocentrotus purpuratus) morphological traits in relation to resource availability.

Flexible resource investment is a risk sensitive reproductive strategy where individuals trade resources spent on reproduction for basic metabolic maintenance and survival. This study examined morphological variation in herbivorous sea urchin grazers across a mosaic landscape of macroalgae dominated habitats interspersed with patches of sea urchin barrens to determine whether sea urchins shift energy allocation in response to food limitation. Extensive underwater surveys of habitat attributes (e.g., sea urchin density, algae cover) were paired with detailed laboratory assays (e.g., sea urchin dissections) to determine how resource abundance affects energy allocation between reproductive capacity and body structure in the purple sea urchin, Strongylocentrotus purpuratus. We found that: (1) sea urchins had a more elongate jaw structure relative to body size in habitats void of macroalgae (i.e., barrens), (2) sea urchin reproductive capacity (i.e., gonad index) was lower in barrens and the barrens habitat was primarily comprised of encrusting algae, and (3) sea urchin jaw morphology (i.e., lantern index) and reproductive capacity (i.e., gonad index) were inversely related. These results suggest that sea urchins respond to macroalgae limited environments by shifting energy allocation between reproductive capacity and modifications of the foraging apparatus, which may explain the ability of sea urchins to acquire food in resource-limited environments.

Interpopulation variability of the reproductive cycle of Arbacia lixula (Echinodermata: Echinoidea) in the Mostaganem shallow-water area (south-western Mediterranean)

The study on the reproductive biology of the black sea urchin Arbacia lixula was carried out at two different sites on the west coast of Algeria (Mostaganem) (one located at Salamandre considered polluted and the other at Stidia is relatively healthy). A monthly sampling was carried out from January 2015 to December 2016. The sex ratio at the two sites is slightly in favour of males. Monthly monitoring of the gonad index showed maximum values during the month of May, and minimum values in September. The gonad index for both male and female evolves in the same way. Histological study of the male and the female gonads confirmed the results obtained for the gonad index. The sexual resting stage takes place in winter, followed by maturation in spring. Finally, the spawning phase occurs between spring and summer. The variability of the seasonal temperature values appears to influence the maturation of the gonads and the spawning process in A. lixula. The results obtained in this study show the existence of an annual cycle in A.lixula with the presence of a massive spawning in July, the duration of which depends on the combined effect of stress factors (increase in temperature and presence of pollution).

A 30-Year Study of Impacts, Recovery, and Development of Critical Effect Sizes for Endocrine Disruption in White Sucker (Catostomus commersonii) Exposed to Bleached-Kraft Pulp Mill Effluent at Jackfish Bay, Ontario, Canada.

Jackfish Bay is an isolated bay on the north shore of Lake Superior, Canada that has received effluent from a large bleached-kraft pulp mill since the 1940s. Studies conducted in the late 1980s found evidence of reductions in sex steroid hormone levels in multiple fish species living in the Bay, and increased growth, condition and relative liver weights, with a reduction in internal fat storage, reduced gonadal sizes, delayed sexual maturation, and altered levels of circulating sex steroid hormones in white sucker (Catostomus commersonii). These early studies provided some of the first pieces of evidence of endocrine disruption in wild animals. Studies on white sucker have continued at Jackfish Bay, monitoring fish health after the installation of secondary waste treatment (1989), changes in the pulp bleaching process (1990s), during facility maintenance shutdowns and during a series of facility closures associated with changing ownership (2000s), and were carried through to 2019 resulting in a 30-year study of fish health impacts, endocrine disruption, chemical exposure, and ecosystem recovery. The objective of the present study was to summarize and understand more than 75 physiological, endocrine, chemical and whole organism endpoints that have been studied providing important context for the complexity of endocrine responses, species differences, and challenges with extrapolation. Differences in body size, liver size, gonad size and condition persist, although changes in liver and gonad indices are much smaller than in the early years. Population modeling of the initial reproductive alterations predicted a 30% reduction in the population size, however with improvements over the last couple of decades those population impacts improved considerably. Reflection on these 30 years of detailed studies, on environmental conditions, physiological, and whole organism endpoints, gives insight into the complexity of endocrine responses to environmental change and mitigation.

Long-term and seasonal changes in the life-history biology of the abyssal holothurian Pseudostichopus aemulatus from the Porcupine Abyssal Plain (North-East Atlantic)

Long-term interannual variations in the benthic community structure are well-known from abyssal plains in the North Atlantic and North Pacific, where rapid responses to changes in the environment by first-order opportunists modify overall species composition. To increase our knowledge of the long-term variations of deep-sea benthic communities in the North-East Atlantic, we studied the response of a second-order opportunist echinoderm, the holothurian Pseudostichopus aemulatus, before, during and after the “Amperima Event” – a four-year episode (1996–1999) where the first-order opportunistic holothurian, Amperima rosea, increased dramatically in density. We used a collection of 14 sampling times of deep-sea community assemblage over a sixteen-year period to understand the temporal variation (i.e., interannual and seasonal) in population structure (i.e., density and individual sizes) and reproduction (i.e., mean oocyte sizes, sex ratios, gonadal indices, and fecundity) in P. aemulatus. Samples were collected from the Porcupine Abyssal Plain (PAP) in the NE Atlantic Ocean at a depth of ca. 4850 m between 1989 and 2005 with a semi-balloon otter trawl (OTSB14) and an epibenthic sledge (BN1.5/C) at varying seasons. We measured individual body size, dissected organisms to prepare histological slides of their gonads, and measured the Feret oocyte diameter in females. We found changes in the life-history biology of P. aemulatus during the “Amperima Event”. Population density increased gradually from September 1997 until April 1999, when P. aemulatus reached a peak in density coinciding with the smallest mean body size observed (1998 and 1999) suggesting recruitment of juveniles. In 1997, before these changes in population structure, mean oocyte sizes were at their largest, suggesting a strong reproductive effort with individuals either preparing to spawn or spawning. This reproductive effort was minimal in the years after 1999, when we found the largest proportions of previtellogenic oocytes in individuals that were probably allocating their energy into growth rather than reproduction given their smaller size. The presence of gametes of all sizes across seasons and a broad range of individual sizes in various sampling times suggests no seasonal reproductive patterns. We suggest that feeding guild differences between various holothurian species explain the diverse life-history responses observed among holothurians competing for resources in a food-poor environment.

Reproductive biology of the rayed pearl oyster (Pinctada imbricata radiata, Leach 1814) in Izmir Bay

Abstract The present study was carried out to determine gonadal stages and quality of pearl oyster meat (Pinctada imbricata radiata, Leach, 1814) in Izmir Bay (Turkey). Pearl oyster samples were collected from the study area at a depth of ~5 m between February 2013 and January 2014. The highest and lowest temperature was measured in July and January as 27°C and 14.2°C, respectively. The maximum chlorophyll a value of 4.640 μg l−1 was calculated in May and the lowest value of 1.009 μg l−1 was recorded in April. Individuals reached their first maturity in April. Spawning activity was observed from June to September and the gonad index (GI) was at the highest level during those months. The development was observed from April to February. The overall female to male ratio was 1.32:1 (p &lt; 0.05) and it did not affect the GI (p &gt; 0.05). There is a strong positive correlation between the GI and temperature (p &lt; 0.05). The highest condition index (CI) was recorded in May as 12.31 ± 0.51, whereas the lowest one in January as 7.37 ± 0.22. As a result, this study revealed that the pearl oyster population in the region is characterized by high reproductive activity, especially during the summer months.

Gonad maturity and gonadal somatic index of blue swimming crab Portunus pelagicus harvested from Spermonde Archipelago, South Sulawesi, Indonesia

Reproductive biology is one of the biological aspects that needed to formulate responsible management of blue swimming crab (BSC). The crab is one of the commercial fisheries commodities in South Sulawesi, Indonesia. Presently no information on the reproductive biology of this crab from Spermonde Archipelago, Sout Sulawesi. Therefore, the study aimed to analyze and compare gonad maturity stage(GMS)andgonadalsomaticindex(GSI)oftheBSCcaughtonthreeecosystemsnamelycoralreef,seagrass,andmangrovein Salemo Island, Spermonde Archipelago. GMS and GSI were analyzed descriptively for five months from March to July 2015. Results indicate there was a difference in GMS of the BSC caught in mangroves, seagrass, and coral reef. Generally, mangrove was dominated by immature BSC with GMS I and GMS II, while the BSC caught in the seagrass and coral reef BSC were dominantly mature and spawn GMS III, IV, and V. GSI BSC caught in mangrove ecosystem are smaller than GSI BSC caught in seagrass and coral reef ecosystems. Seagrass and coral reef ecosystems suitable for development no-take zone of the BSC.

The balancing act: Protein, lipid and seaweed dietary levels to maximize gonad quantity in a wild‐caught sea urchin

Sea urchin gonads (roe) are a prized global sea food commodity, with growing demand driving the need for urchin roe enhancement aquaculture. Effective roe enhancement of urchins using formulated feeds require species‐specific optimization and an understanding of the interactions between key dietary components (e.g. protein, lipid, carbohydrate, energy and/or algal supplements). Here, we tested 18 formulated feeds on the sea urchin Heliocidaris erythrogramma, collected from barrens. The 18 iso‐energetic (~20 MJ/kg) feed combinations contained one of three protein levels (250, 375 or 500 g/kg), three lipid levels (73, 101 or 131 g/kg) combined with a single (45 g/kg Sargassum spp.) or multiple (45 g/kg Sargassum spp., 25 g/kg Solieria robusta, 25 g/kg Ulva lactuca) dried algal supplement. From two consecutive 12‐week enhancement trials, the most optimal feed type contained 375 g/kg protein, 73 g/kg lipid and a 45 g/kg algal supplement (Sargassum spp.) and produced gonad indices of 18.5 ± 0.4% (Trial 1) and 21.7 ± 1.2% (Trial 2). Across feed types, there was no significant difference in the proportion of marketable quality (A and B grade) roe produced (56%–85% Trial 1, 65%–85% Trial 2). We conclude that roe enhancement of H. erythrogramma collected from barrens is highly feasible.

Microcystin-LR induces ovarian injury and apoptosis in mice via activating apoptosis signal-regulating kinase 1-mediated P38/JNK pathway

As an emerging pollutant in the aquatic environment, microcystin-LR (MC-LR) can enter the body through multiple pathways, and then induce apoptosis and gonadal damage, affecting reproductive function. Previous studies focused on male reproductive toxicity induced by MC-LR neglecting its effects on females. The apoptotic signal-regulated kinase 1 (ASK1) is an upstream protein of P38/JNK pathway, closely associated with apoptosis and organ damage. However, the role of ASK1 in MC-LR-induced reproductive toxicity is unclear. Therefore, this study investigated the role of ASK1 in mouse ovarian injury and apoptosis induced by MC-LR. After MC-LR exposure, ASK1 expression in mouse ovarian granulosa cells was increased at the protein and mRNA levels, and decreased following pretreatment by antioxidant N-acetylcysteine, suggesting that MC-LR-induced oxidative stress has a regulatory role in ASK1 expression. Inhibition of ASK1 expression with siASK1 and NQDI-1 could effectively alleviate MC-LR-induced mitochondrial membrane potential damage and apoptosis in ovarian granulosa cells, as well as pathological damage, apoptosis and the decreased gonadal index in ovaries of C57BL/6 mice. Moreover, the P38/JNK pathway and downstream apoptosis-related proteins (P-P38, P-JNK, P-P53, Fas) and genes (MKK4, MKK3, Ddit3, Mef2c) were activated in vivo and vitro, but their activation was restrained after ASK1 inhibition. Data presented herein suggest that the ASK1-mediated P38/JNK pathway is involved in ovarian injury and apoptosis induced by MC-LR in mice. It is confirmed that ASK1 has an important role in MC-LR-induced ovarian injury, which provides new insights for preventing MCs-induced reproductive toxicity in females.

Seasonal composition of immature germ cells in the Yesso scallop identified by vasa-like gene (my-vlg) and protein expression, with evidence of irregular germ cell differentiation accompanied with a high mortality event

The objective of this study was to understand germ cell renewal and differentiation in the Yesso scallop Mizuhopecten yessoensis throughout its reproductive cycle. First, we identified a Yesso scallop vasa-like gene (my-vlg) as a useful marker for immature germ cells. Both in situ hybridization and immunohistochemistry confirmed the germ-cell-specific expression of my-vlg and protein, especially in spermatogonia, oogonia, and primary oocytes. An immunohistochemistry with anti my-Vasa antibody further revealed that immature germ cells (i.e., gonial cells) are located on the basal membrane of germinal acini and are present during all maturational stages in both the ovary and testis. Quantitative analysis revealed a shift in germ cell number and change in germ cell composition associated with the gonadal maturation process, indicating a persistence of my-Vasa-positive immature germ cells throughout the reproductive cycle. In the testis, a gradual increase in my-Vasa-positive immature germ cells was seen from November to March. In the ovary, an increase in my-Vasa-positive immature germ cells was observed from September until November. We also used gonad index (GI) to summarize and evaluate the maturational changes of scallops in the 2018 generation. This generation had a background of relatively high mortality and shell deformity in the previous year, and we noted a small irregular peak of GI in the summer (July–August). We confirmed that the germ cells proliferating in the summer were my-Vasa-positive, implying that germ cell developmental progression occurred in the 2018 generation during the non-reproductive period. In conclusion, this study establishes an immuno-identification method for my-Vasa-positive immature germ cells and reveals germ cell composition in a bivalve species throughout its reproductive cycle. These results will support monitoring techniques for gonad development and the reproductive status of brood stock in shellfish seed production hatcheries.

Reproductive Cycle of Sea Urchin Paracentrotus lividus (Lamarck, 1816) from the South Coast of Morocco: Histology, Gonads Index, and Size at First Sexual Maturity

The main objective of this study was to describe the reproductive cycle of the sea urchin Paracentrotus lividus (Lamarck, 1816) on the south Atlantic coast of Morocco. In this study, we selected three sites in the Agadir region: Sidi R’bat, Cap Ghir, and Anza to study from March 2018 to February 2019 some aspects of reproduction in this species through sex-ratio, the histological identification of the stages of sexual maturity, their monthly evolution, the evolution of the gonad index, as well as the size at first sexual maturity. The results show that at the three study sites, the sex-ratio is unbalanced in favor of females. The histology of the gonads revealed six different stages: recovering, growing, premature, mature, partly spawned, and spent. The gonadal cycle is synchronous for both sexes; histological examination confirmed the presence of spawning (March–October) in three sites. A perfect correlation observed between the gonad index, and the histological results suggest that the gonad index decreases when the individual is spawning. Temperature and photoperiod are important factors controlling the reproduction cycle. The beginning of spawning in the three sites coincides with the increase in temperature and photoperiod, which may act as environmental triggers. On the other hand, the size at first sexual maturity was ranged between 30 and 40 mm, and the values of L50 of females are higher than L50 of males signifying that males reach sexual maturity before females.

Reproductive Strategy of Dosinia ponderosa (Gray, 1838) (Veneridae) in Puerto Libertad, Sonora, Mexico

The reproductive strategy of Dosinia ponderosa at a site of the eastern coast of the Gulf of California, Puerto Libertad, Sonora is reported. Samples of visceral mass were taken from 30 clams that were collected monthly from March 2015 to March 2016, and the length and weight of the tissue without shell of each organism were recorded. Through histological analysis, the gonadal index were calculated, and the reproductive stages of the ponderous dosinia were determined. Six oocyte substages and five gonadal development stages for females and five for males are described. The sex ratio was 1:1, and no undifferentiated specimens were found. The sexual maturity phase was observed throughout the year, with two reproductive peaks in June–July and October–November. No correlation was observed between the reproductive activity and temperature or primary productivity.

Microcystin-leucine arginine exposure contributes to apoptosis and follicular atresia in mice ovaries by endoplasmic reticulum stress-upregulated Ddit3

Microcystin-leucine arginine (MC-LR), an intracellular toxin to cause reproduction toxicity, is produced by blooming cyanobacteria and widely distributed in eutrophic waters. It is revealed that MC-LR-induced female reproductive toxicity is more severe than male reproductive toxicity. Previous studies mainly focused on male reproductive toxicity, and the molecular mechanisms of MC-LR-induced apoptosis, follicular atresia and infertility in female remain largely unclear. Here, it was found that MC-LR treatment could induce apoptosis, inflammation, follicular atresia, and decrease of gonadal index in mice ovaries. RNA-Seq data showed that the up-regulation of DNA-damage inducible transcript 3 (Ddit3) under endoplasmic reticulum (ER) stress had predominantly regulatory role in MC-LR-induced apoptotic pathway. Furthermore, MC-LR exposure promoted cleavage of activating transcription factor 6 (ATF6, 50kd), inositol-requiring enzyme 1 (Ire1) expression, phosphorylation of IRE1, mitogen-activated protein kinase 5 (Map3k5) and Ddit3 expression, which was accompanied by the upregulation of death receptor 5 (Dr5) and active-caspase-3, and a decrease in Bcl-2 expression. ER stress inhibitor 4-Phenyl butyric acid (4-PBA) ameliorated these MC-LR-induced changes in protein or mRNA level. More importantly, knockdown of Ddit3 suppressed MC-LR-induced cell apoptosis and follicular atresia by directly regulating Dr5 and Bcl-2. Additionally, it was also found that MC-LR increased Map3k5 phosphorylation by inhibiting protein phosphatase 2A (PP2A) activity, and then promoted Ddit3 expression. In short, our data suggests that Ddit3 promotes MC-LR-induced mice ovarian cells apoptosis and follicular atresia via ER stress activation, which provides a new insight into the relation between infertility in females and the emerging water pollutant MC-LR.

Food selectivity and reproductive biology of small indigenous fish Indian river shad, Gudusia chapra (Hamilton, 1822) in a large tropical reservoir.

Assessment of life history strategies of economically important small indigenous fishes (SIF) which are rich in nutritive values is essential and imperative to artisanal and subsistence small-scale inland fisheries of Indian tropical reservoirs. The present investigation aims to estimate the food selectivity in juveniles and adults, reproductive traits such as sexual maturity, gonadosomatic index, ova diameter, and fecundity of Gudusia chapra from a large impounded ecosystem of India. A total of 668 (Juvenile 129, adult 539) specimens, 37 to 142mm standard length and 0.89-25.68g body weight were collected during October 2014-September 2015. The qualitative estimation of the stomach contents revealed herbi-omnivorous feeding behavior of fish. The mean relative gut length (mRGL) of the species was 1.557 ± 0.024 in juveniles and 1.154 ± 0.012 in adults. The sex ratio was 1:1.30 with dominance of females in the population though insignificant. The total length at which 50% individual attain maturity (TL50) was estimated as 80.50mmbased on the logistic curve. The absolute fecundity of the individuals ranged from 749 to15044, and ova diameter ranged from 0.10-2.00mm. The gonadal indices (GSI, MGSI, and DI) indicated that spawning extended throughout the year with peak reproductive activity in October, March-April, and July (mean absolute fecundity ranged from 4000 to 6000). The present study characterized biological and reproductive traits of G. chapra from a large reservoir ecosystem and demonstrated a new trend of reproductive pattern which will serve as benchmark data for future assessment and management planning of this species in impounded waters. The study also suggested some specific management measures for sustainable exploitation and conservation of small indigenous species.

The gametogenic cycle of the non-native false limpet Siphonaria pectinata (Linnaeus, 1758) in the easternmost limit of its distribution range: implications for its future in the Eastern Mediterranean Basin

The gametogenic cycle of the false-limpet Siphonaria pectinata from the Bizerte channel (Northern Tunisia) was studied through histological characterization of the hermaphroditic gonad during a 1-year study period (May 2015 - May 2016). Spawningintensity in the field as well as the gonadic index were calculated monthly. Both female and male gametes were observed simultaneously within acini of adult individuals and continuously throughout the year. Oogenesis started in the mid-autumn (October), with gonads characterized mainly by proliferation of female cells. After that, oocytes progressively increased in number and volume until summer, when the evacuation stage frequency was the highest. From summer to autumn, some acini were empty fromtheir oocyctes while some others had already begun the proliferation stage, suggesting the lack of a resting phase. Spermatogenesiswas also a continuous process throughout the year, with spermatozoa being mainly observed in late spring (March). These findings suggested that environmental conditions are suitable for the establishment of S. pectinata, first mentioned in 1998 on the Tunisian coast and even suggest that it could continue spreading eastward in the Mediterranean Basin.

Size at maturity, maturity stages and sex ratio of tigerfish Hydrocynus vittatus Castelnau, 1861 in Lake Kariba, Zimbabwe: assessing the influence of decades of fisheries exploitation

Size at maturity, sex ratio and maturity stages are key population parameters in fisheries management of exploited stocks because they influence survival of fish populations. The decline in Hydrocynus vittatus catches during the tigerfish competition and along the shoreline of Lake Kariba, Zimbabwe prompted this study. This study investigated population parameters of H. vittatus in the Sanyati Basin, Lake Kariba. A gonadal reproductive stage determination index was used to determine sexual maturity and the logistic growth curve was used to estimate size at 50% sexual maturity (L50). The study revealed that the L50 value had decreased from 30 cm to 22.1 cm for males and 35 cm to 27.8 cm for females since 1961. Males and females had an L50 of 22.1 cm and 27.8 cm, respectively. The male to female ratio was 1:0.8, which is typical of stressed populations. Increased fishing pressure in the Sanyati Basin, Lake Kariba is a potential threat to the H. vittatus population. More research and monitoring of the population parameters of tigerfish is required, in order to predict long term effects of overexploitation and to enable responsible authorities to protect the fish stock from collapsing.

Fecundity, length at maturity and gonadal development indices of river catfish (Clupisoma garua) of the old Brahmaputra River in Bangladesh

The present study aims to estimate the fecundity, maturity and gonadal indices of Clupisoma garua population existing in the old Brahmaputra River, Bangladesh. The samples were collected once every month from the 1st April 2016 to the 31st March 2017 and yielded a total of 90 females and 19 males. The standard length (SL) and the body weight (BW) of females ranged from 11.8 to 27.8 cm and 23.0 to 272.2 g, respectively. The lowest value of the GSI means for females was found in November (0.22) while the highest value was in June (1.87). The scatter plot of the SL with corresponding GSI revealed that the length at maturity for females was attained in 17.1 cm of standard length. The lowest value of fecundity was 6159 and the highest was 22,166 oocytes. The relationship between BW and fecundity was F = 167.6BW – 9211 (coefficient determinant, r2 = 0.537), while the relationship between SL and fecundity was expressed as F = 0.04619SL2.177 (r2 = 0.551). Based on the GSI means, it was manifested that the possible spawning season was from May to August with a peak in June.

Reproductive Study of Megapitaria aurantiaca (Sowerby, 1831) (Bivalvia: Veneridae) in Puerto Libertad, Sonora, Mexico

Reproductive aspects of the golden clam Megapitaria aurantiaca in Puerto Libertad, Sonora, Mexico, were analyzed from March 2015 to March 2016. Through histological analysis, five phases of gonadal development were defined (cytolytic, preactive, active, emission, and postactive), the sexual portion was obtained, the relationship between environmental variables (temperature and chlorophyll a) and reproduction was determined through the gonadal index, and the diameter of the oocytes was measured. A seasonal reproductive cycle was exhibited by M. aurantiaca with a spawning phase from April to October which coincided with an increase in the temperature. Spawning clams were observed at a shell length of 69 mm. A sex ratio of 1:1 was recorded. Finally, for the first time, the presence of hermaphroditic organisms was reported for this species.