Spawning Stage Research Articles

Do broodstock diets influence viability and larval development of Holothuria mammata?

The intensive exploitation of sea cucumbers, mainly exported to Asian seafood markets, has contributed to deplete natural populations of several species. In Europe, the aquaculture production of these echinoderms is minimal, reflecting the low scientific production on the topic. In Portugal, like in Mediterranean countries, there are native species with high commercial value, which can be potential candidates for aquaculture. The control over the reproductive cycle is an important tool for rearing success, which, in turn, decreases the pressure over natural stocks. However, there are very few studies on the larval development of European species and none on the broodstock maturation in captivity. The present work studied the influence of three diets on the gonadal maturation and larval viability and development of Holothuria mammata.After 120-days of captivity the broodstock groups fed with a mixture of live microalgae (Diet 2) and a mixture of live microalgae and extruded dry food (Diet 3) reached the spawning stage, in contrast to the group fed with a mixture of frozen microalgae (Diet 1). Spawning was induced by thermal shock. Larval rearing from broodstock fed on Diet 2, total mortality was observed on the 12th day, after the onset of mid auricularia stage. The stocks of larvae from the broodstocks fed diets 1 and 3 reached the stage of pentactula on the 27th day. The success in spawning induction and embryonic development suggest that H. mammata may accept different types of diets as frozen microalgae mixes or live microalgae and dry feeds and still produce viable offspring. However, it is essential to develop more studies on the reproductive biology of H. mammata to optimize the hatcheries techniques to broodstock conditioning and larval rearing in captivity.

Mobilisation and dynamics of energy reserves in different tissues of Donax trunculus (Bivalvia: Donacidae) in the Gulf of Tunis (eastern Mediterranean Sea, Tunisia)

Seasonal changes in condition index and the biochemical components (proteins, lipids and glycogen) of the gonad/digestive gland, foot, labial palp, mantle, gills and adductor muscles of Donax trunculus Linnaeus, 1758 from the Gulf of Tunis were monitored seasonally, from November 2006 to October 2007, in relation to environmental conditions and reproductive events. The condition index increased during late gametogenesis and the ripe stage, coinciding with enrichment of the water by phytoplankton, and decreased during late summer and autumn (i.e. the spawning and rest periods). Glycogen increased during early gametogenesis and peaked during winter, pointing to its mobilisation in the formation of active ripe gametes. The foot, gonad/digestive gland, and adductor muscle were the three major glycogen-reserve tissues. Protein content was high during the end of summer in the whole individual and during autumn in the gonad/digestive gland. Lipid content started to increase as gametogenesis began, reached its peak at gonad ripeness and during the early spawning stage (summer) and sharply declined due to the shedding of gametes (autumn). A transformation of glycogen for de novo synthesis of lipids, in the gonad/ digestive gland, was suggested during the later stages of the gonadic cycle, in support of gametogenesis. Temporal fluctuations in environmental factors, particularly temperature and food supply, drive the cycle of storage and utilisation of metabolic energy reserves which in turn govern gametogenesis in Donax trunculus.

Size Structure and Gonad Characterization of <i>Gari elongata</i> (Lamarck 1818) from the Coastal Areas of Hinatuan, Surigao Del Sur, Philippines

Size-structure analyses and gonad characteristics of the elongate sunset clam Gari elongata from the coastal waters of Hinatuan, Surigao del Sur, Philippines, was determined in this study. An opportunistic sampling approach was applied during the collection of G. elongata from the coastal waters of Brgy. Loyola and Brgy. Aquino. A total of 1437 G. elongata individuals were subjected to length-weight measurements, and gonads from five (5) individuals per sex among size classes were processed for histological characterization. The maximum total length of G. elongata recorded is 5.42 cm, way smaller than its congeners elsewhere, which is at 7.0-9.2 cm. The size-structure analysis shows that G. elongata from Brgy. Loyola exhibited negative allometric growth while those gleaned from Brgy. Aquino exhibited positive allometry indicating variation in growth dynamics. Known as a gleaning source, Barangay Loyola is abundant in G. elongata, but individuals are much smaller compared to those gathered from Barangay Aquino. A ratio of 1:1 for male and female classification was observed, as seen from gonad histological analyses. Ovaries were found in the spawning capable state with gonads in ripe (30%), spent (25%), early development (25%), and partially spawning (20%) stages. Testes were found to be in the ripe (40%), early developing (10%), spent (10%), and partially spawning (40%) stages. Gari elongata exhibits spawning capable gonads at 2.85 cm and 2.95 cm for males and females, respectively, which suggests that the shellfish has adapted early to reproduction to maintain its population in the coastal waters of Hinatuan. The small body lengths of individuals with mature gonads indicate that G. elongata may have been exposed to some stress in their natural environment. Regulated management of G. elongata to avoid over-harvesting and assessment of water and sediment quality of their natural habitat is highly recommended

Size Structure and Gonad Characterization of <i>Gari elongata</i> (Lamarck 1818) from the Coastal Areas of Hinatuan, Surigao Del Sur, Philippines

Size-structure analyses and gonad characteristics of the elongate sunset clam Gari elongata from the coastal waters of Hinatuan, Surigao del Sur, Philippines, was determined in this study. An opportunistic sampling approach was applied during the collection of G. elongata from the coastal waters of Brgy. Loyola and Brgy. Aquino. A total of 1437 G. elongata individuals were subjected to length-weight measurements, and gonads from five (5) individuals per sex among size classes were processed for histological characterization. The maximum total length of G. elongata recorded is 5.42 cm, way smaller than its congeners elsewhere, which is at 7.0-9.2 cm. The size-structure analysis shows that G. elongata from Brgy. Loyola exhibited negative allometric growth while those gleaned from Brgy. Aquino exhibited positive allometry indicating variation in growth dynamics. Known as a gleaning source, Barangay Loyola is abundant in G. elongata, but individuals are much smaller compared to those gathered from Barangay Aquino. A ratio of 1:1 for male and female classification was observed, as seen from gonad histological analyses. Ovaries were found in the spawning capable state with gonads in ripe (30%), spent (25%), early development (25%), and partially spawning (20%) stages. Testes were found to be in the ripe (40%), early developing (10%), spent (10%), and partially spawning (40%) stages. Gari elongata exhibits spawning capable gonads at 2.85 cm and 2.95 cm for males and females, respectively, which suggests that the shellfish has adapted early to reproduction to maintain its population in the coastal waters of Hinatuan. The small body lengths of individuals with mature gonads indicate that G. elongata may have been exposed to some stress in their natural environment. Regulated management of G. elongata to avoid over-harvesting and assessment of water and sediment quality of their natural habitat is highly recommended

Combining otolith elemental signatures with multivariate analytical models to verify the migratory pattern of Japanese Spanish mackerel (Scomberomorus niphonius) in the southern Yellow Sea

Japanese Spanish mackerel, Scomberomorus niphonius, is a commercially important, highly migratory species that is widely distributed throughout the northwestern Pacific region. However, its life history and migratory patterns are only partially understood. This study used otolith chemistry to investigate the migratory pattern of S. niphonius in the southern Yellow Sea, an important fishing ground. Transverse sections of otoliths from 15 age-1 spawning or spent individuals, comprising up to one complete migration cycle, were analyzed from the core to the margin by using laser ablation inductively coupled plasma mass spectrometry. The ratios of the element to Ca were integrated with microstructural analysis to produce age-related elemental profiles. Combining multielemental analysis of otolith composition with multivariate analytical models, we quantified structural changes in otolith chemistry profiles. Results revealed there were diverse changing patterns of otolith chemistry profiles for detected elements and the elements of Na, Mg, Sr and Ba were important for the chronological signal. Five clusters were identified through chronological clustering, representing the five life stages from the early stage to the spawning stage. Variation of Ba:Ca ratio was most informative, showing a step-decreasing pattern in the first four stages and a rebound in the spawning stage. These results support the hypothesized migratory pattern of S. niphonius: hatching and spending their early life in the coastal sandy ridges system of the southern Yellow Sea, migrating northeastward and offshore for feeding during juvenile stage, aggregating in early October and migrating outward to the Jeju Island for wintering, and returning to the coastal waters for spawning. This study demonstrated the value of life-history related otolith chemistry profiles combined with multivariate analytical models was a means to verify the migration patterns of S. niphonius at regional scales with potential application in fisheries assessment and management.

Influence of Parental Fatty Acid Desaturase 2 (fads2) Expression and Diet on Gilthead Seabream (Sparus aurata) Offspring fads2 Expression during Ontogenesis.

Simple SummaryThe present study was on the gene expression of a rate-limiting enzyme in long chain polyunsaturated fatty acids (LC-PUFAs), fatty acyl desaturase 2 (fads2), throughout the embryonic development of a gilthead sea bream. The results showed a maternal transfer of fads2 mRNA to the developing oocyte. The embryonic fads2 expression might start after the neurula stage. No effect was found in fads2 expression in developing eggs from broodstock fed with a diet rich in rapeseed oil or fish oil. The present study provides information on the change of LC-PUFA biosynthesis during embryogenesis.Previous studies have shown that it is possible to increase the ability of marine fish to produce long-chain polyunsaturated fatty acid from their 18C precursors by nutritional programming or using broodstock with a higher fatty acyl desaturase 2 (fads2) expression. However, those studies failed to show the effect of these interventions on the expression of the fads2 gene in the developing egg. Moreover, there were no studies on the temporal expression of the fads2 during ontogeny in the gilthead sea bream (Sparus aurata). In order to determine the changes in expression of fads2 during ontogeny, gilthead sea bream broodstock with a high (HRO) or low (LRO) fads2 expression fed a diet previously used for nutritional programming, or a fish oil-based diet (LFO) were allowed to spawn. The samples were taken at the stages of spawning, morula, high blastula, gastrula, neurula, heart beating, hatch and 3 day-old first exogenous feeding larvae to determine fads2 expression throughout embryonic development. The results showed the presence of fads2 mRNA in the just spawned egg, denoting the maternal mRNA transfer to the developing oocyte. Later, fads2 expression increased after the neurula, from heart beating until 3-day-old larvae, denoting the transition from maternal to embryonic gene expression. In addition, the eggs obtained from broodstock with high fads2 expression showed a high docosahexaenoic acid content, which correlated with the downregulation of the fads2 expression found in the developing embryo and larvae. Finally, feeding with the nutritional programming diet with the partial replacement of fish oil by rapeseed oil did not affect the long chain polyunsaturated fatty acid (LC-PUFA) contents nor fads2 expression in the gilthead sea bream developing eggs.

Study on length weight relationship and feeding habits of a threaten fish Ompok pabda from Tripura, India

Ompok pabda is a highly consumer preferred fish. The biological parameters such as length and weight, condition factor (Kn), growth pattern and types of growth of Ompok pabda is necessary to know for the aquaculture practices. So, to study the bionomics (i.e., food and feeding habit, the relative length of gut, stomach content and feeding intensity) of Ompok pabda (Hamilton, 1822) the fish were sampled from the Gomati River and Rudrasagar lake of Tripura. The relationship between the length and weight of the species was studied by applying non linear model. The parameter estimates, mean square error (MSE) and mean absolute error (MAE) were also computed for finding the better model. The average relative condition factor (Kn) was also estimated. The length and weight relation of different age group were calculated for Ompok pabda. The food and feeding habit and the relative length of gut, stomach, and feeding intensity were examined by using standard methods. The morphology and morphometrics of the alimentary canal have also been studied along with the gut content analysis using standard methods. The Relative length of Gut of the dissected fish was studied meticulously and recorded the food contents as per point’s methods. Out of total 362 sample specimens of Ompok pabda, the total length was varied from 7.7-20.7 cm. The morphology and morphometrics of the alimentary canal have also been studied along with the gut content analysis. The gastro-somatic index observed maximum (11.7%) in February and recorded in higher values from January to March. This phase revealed the early maturing stages of gonad and lowest GaSI (%) recorded during the advance spawning stage of gonads during the months of May to August (2.1 to 0.81). The result of the present study reveals the isometric pattern of growth and food and feeding habit of the fish indicate that O. pabda is a carnivorous fish. It was found that the effect of length on weight is statistically significant at 5% level of significance (

Transient increase in abundance of B lineage but not myeloid-lineage cells in anterior kidney of sockeye salmon during return migration to the natal grounds

As anadromous fish, sockeye salmon undergo complex endocrine changes when they return to their natal grounds to spawn. This is correlated with major immunological changes that will affect their response to pathogens. In spite of these challenges, salmon need to maintain sufficiently robust immunity to survive until spawning is complete, but the nature of immune adaptations during the spawning stage remains poorly understood. Our central question is to determine if sockeye salmon stimulate their immune system during the return migration and if so, whether this is a protective response. To begin answering this question, here we characterized the nature and timing of potential changes in anterior kidney immune fingerprints between salmon collected from seven different sites along the Kenai river, including the mouth of the river and two spawning sites. Our results revealed significant changes in abundance of B lineage, but not myeloid lineage cells during the spawning journey. This included early, transient and significant increases in abundance of both IgM+ and IgT+ B cells soon after fish entered the river, followed by a transient, significant increase in abundance of IgM++ secreting cells in fish caught mid-river, and ending with a return to base levels of both cell populations in fish caught at spawning sites. Further, males appeared to have higher immune activation than females, as reflected by higher abundance of IgM++ secreting cells, higher spleen index, and higher titers of serum IgM. Although roles for these newly generated IgM++ secreting cells remain unclear at this time, the data complement our previous work which supported roles for long-lived plasma cells to protect returning salmon from pathogens at their natal grounds. We conclude that sockeye salmon are capable of inducing B cell responses during their spawning journey, with males having stronger responses compared to females. B cell activation during the return journey may provide returning adults with additional protection against pathogens not encountered as juveniles.

Temporal transcriptome analysis in female scallop Chlamys farreri: First molecular insights into the disturbing mechanism on lipid metabolism of reproductive-stage dependence under benzo[a]pyrene exposure

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widespread persistent organic pollutants (POPs) in marine environment. Benzo[a]pyrene (B[a]P), the most toxic carcinogen of PAHs, is widely studied as a representative that interferes with lipid metabolism. However, the underlying molecular mechanisms of lipid metabolism by B[a]P interference towards bivalve, one of the marine-pollution bio-indicators have not been elucidated yet, especially during gonadal development which is closely associated with lipids. In this study, female scallops Chlamys farreri were cultured with natural and 4 μg/L B[a]P exposed seawater, respectively, and a multi-stage (proliferative, growth, mature, and spawn stage) ovarian transcriptome profiling was performed to decipher the reproductive stage-dependence disturbing mechanisms on lipid metabolism caused by B[a]P in bivalves. The results revealed the potential molecular mechanism of B[a]P-induced triglycerides (TGs) accumulation, which probably resulted from the collaboration of promoting synthesis and inhibiting metabolization of TGs, notably, this mechanism also occurred at spawn stage. Correspondingly, B[a]P and TGs contents measured in ovary offered direct biochemical evidences for the interference effects and stage-dependent accumulation patterns of B[a]P. Moreover, the gene expressions of fatty acids synthesis related enzymes were down-regulated cooperatively, illustrating the molecular compensatory mechanism that reduced susceptibility from oxidative damage. And these results further emphasized the important role of prostaglandins (PGs) in immune response mediated by arachidonic acid metabolism. In addition, this study explored the underlying molecular mechanism affected by B[a]P on sterol metabolism, which possibly posed a threat to normal reproductive functions in bivalves. Taken together, our findings filled the gap of the stage-dependent interference molecular mechanisms on lipid metabolism behind bivalves, and provided a new perspective for investigating the adaptive mechanisms of bivalves under POPs stress.

Characterizing transcriptome in female scallop Chlamys farreri provides new insights into the molecular mechanisms of reproductive regulation during ovarian development and spawn

Bivalve mollusks are descendants of an early-Cambrian lineage and have successfully evolved unique strategies for reproduction. Nonetheless, the molecular mechanisms underlying reproductive regulation in mollusks remain to be elucidated. In this study, transcriptomes of ovary at four reproductive stages in female Chlamys farreri were characterized by RNA-Seq. Regarding signaling pathways, ECM-receptor interaction pathway, mTOR signaling pathway, Fanconi anemia pathway, FoxO signaling pathway, Wnt signaling pathway and Hedgehog signaling pathway were enriched during ovarian development processes. In addition, pathways related to energy metabolism such as Nitrogen metabolism and Arachidonic acid metabolism were enriched at spawn stage. Interestingly, Neuroactive ligand-receptor interaction was significantly enriched involved in ovarian development and spawn, and indicated the potential functions of nervous system on reproductive regulation in C. farreri. What's more, this study identified and characterized fourteen genes involved in "sex hormones synthesis and regulation", "ovarian development and spawn" and "maternal immunity" during the four reproductive stages in C. farreri. We determined that CYP17 uniquely affected gamete release by influencing the physiological balance among the steroid hormones and showed that receptors of the 5-HT and GABA neurotransmitters were tightly associated with ovarian maturation. Furthermore, to the best of our knowledge, this is the first study to report the maternal effect gene Zar1 in bivalve mollusks, likewise the maternal immunity genes displayed coordinated and cooperative expression during reproductive periods, which strengthened the environmental adaptation mechanisms of bivalves. Taken together, this study provides the first dynamic transcriptomic analysis of C. farreri at four key reproductive stages, which will assist in revealing the molecular mechanisms underlying bivalves on reproductive regulation in ovarian development and spawn.

Induction of spawning in Pacific white shrimp Litopenaeus vannamei (Boone, 1931) by injection of its molt inhibiting hormone isoform II produced in E. coli

The optimization of reproductive parameters in shrimp farming continues to be a challenge for most producing countries. Although the crustacean neuropeptides have been studied extensively in the last two decades, the functions of most of these neuropeptides remained putative. Among them, molt-inhibiting hormone isoform II (MIH II) has shown an important role in vitellogenesis. In this study, the cDNA encoding mature MIH II peptide was isolated by RT-PCR from the L. vannamei eyestalk. The cDNA was cloned into pET28a bacterial expression vector. Recombinant MIH II was obtained in the form of insoluble inclusion bodies and purified to ~88% purity. Two doses of rMIH II and a negative control group were assayed in vivo. The stages of ovarian maturation and spawning were recorded during 72 hr post-injection. The results showed that ovarian maturation occurred approximately in 9% and 33% of females injected with rMIH II at the doses of 300 and 600 ng/gbw respectively. Neither maturation nor spawning was detected in the negative control group. Females injected with 600 ng/gbw, which showed vitellogenic stages III and IV, spawned. These preliminary results argue that the hormone rMIH II could be a promising candidate to induce spawning in L. vannamei shrimp.

“There and back again” − How decapod megalopae find the way home: A modelling exercise for Pachygrapsus marmoratus

Pachygrapsus marmoratus is a common coastal crab occurring in rocky shores of the northeastern Atlantic. The species presents a planktonic larval phase, constituting an interesting subject for dispersal studies, given the larval release in intertidal areas, followed by the exportation to shelf waters where larval development takes place. Onshore migration to the adult habitats is thought to be performed by the megalopa stage.Observations obtained during a summer zooplankton survey showed P. marmoratus larvae gradually farther from the coast throughout larval development, with early larval stages found in surface layers and megalopae occurring closer to the coast. The vertical migration mechanisms for larval dispersal and the return to settlement habitats were tested through physical-ecological models where the vertical distributions changed through the larval development. Ecological data, such as the ontogenetic vertical distribution of each larval stage, larval duration, and time and sites of spawning, were integrated in an oceanic model. Simulations tested different vertical distributions and periods, covering the entire larval development from intertidal areas to shelf and back to shore. The distribution of the early stages in surface layers promoted cross- and alongshore transport. Differences in the initial advection determined the positions where the more advanced stages were found later in the development. The subsurface distribution of advanced stages facilitated the transport to the inner shelf, limiting the cross-shore upwelling transport and promoting higher return to the adult habitats. Different periods of larval release resulted in contrasting dispersal patterns that could influence larval survival and recruitment to adult populations.

Ege Denizi’nde (Akdeniz) Holothuria polii (Delle Chiaje, 1823) türü deniz hıyarının yumurtlama dönemindeki gonad gelişimi

The Mediterranean sea cucumbers including Holothuria polii has become commercially important in international trade due to the high demand of consumers from Far East countries. Sea cucumbers fisheries is a valuable income for the regional fishermen but natural stocks endangered by overfishing in recent years. Fisheries regulations and aquaculture studies are important precautions for preserving natural stocks. All these efforts are based on reproduction biology of this species which slightly differed among regions. In this study, the reproduction biology including morphological characteristics, gonadosomatic index and gonadal development stages of H.polii at the eastern coast of Aegean Sea (Izmir, Turkey) were investigated during the reproduction (spawning) period from July to October 2018. Gonads and gonad sections of 60 sea cucumbers (120.60 ± 19.56 g) have been observed by macroscopic and microscopic inspections. Three gonadal development stages have been identified by histologic observations as mature (III), spawning (IV) and post-spawning stage (V) in gonadal tubules. Results indicate that both female and male gonads are at mature and spawning stage in July and all gonads are at post-spawning stage in October. The mean gonad weight was 12.53 ± 1.33 g at the beginning of the spawning period (July) and 1.87 ± 0.58 g at the end of the spawning period (October). Gonadosomatic index decreased from 17.53 ± 0.02% (July) to 3.37 ± 0.01% (October) after spawning. The gonadosomatic index, gonad weight, and spawning were related to the seawater temperature. According to this study, the spawning period of H.polii at the eastern coasts of the Aegean Sea starts in July and completely ends in October. As a result, the data related to the reproduction biology in spawning period of H.polii would guide stock management and artificial breeding of this species under controlled conditions.

Reproductive Biology and Ecology of the Green Mussel Perna viridis: A Multidisciplinary Approach.

A multidisciplinary approach was applied to explore deeper knowledge about the reproductive biology and ecology of the green mussel (Perna viridis) by interlinking among ecological factors, ingested gut plankton, gonad fatty acid profile, and reproductive traits. Mussels were collected throughout the year from the coastal region of the Bay of Bengal of Bangladesh, and the histological analysis of 242 mussels revealed five stages of gametogenesis with an annual spawning season from January to April. The gonadosomatic index showed a strong correlation with the water quality parameters, ingested gut plankton groups, and gonadal fatty acids, and also displayed prominent effects of seasonality. In all datasets, we performed principal component analysis in which the first two principal components showed that seasonality explained >65% of the variability, and the multivariate spaces of seasonality corresponded to the gonad development. High salinity, nutrients, chlorophyll a, and plankton abundance in the water column were positively correlated with gonad development and the spawning of mussels. During the development stage, mussel ingested more plankton, particularly Bacillariophyceae and Pyrrophyceae, which were an important source of increased n-3 polyunsaturated fatty acids content in gonads. Furthermore, gonads accumulated more lipids and saturated fatty acids during the mature and spawning stages, which were probably utilized during embryogenesis and early larval development as energy sources and constituents of the cell membrane. This research provides a model toward a better understanding of reproductive biological traits and how these traits are interrelated with the surrounding environmental variables of the green mussel, which would be helpful in marine aquaculture and the sustainable exploitation of the fishery resources.

A possible new spawning area for Atlantic bluefin tuna (Thunnus thynnus): the first histologic evidence of reproductive activity in the southern Gulf of Mexico.

The number of studies of reproductive biology for Atlantic bluefin tuna carried out in the Gulf of Mexico is significantly lower than those undertaken in the Mediterranean Sea. Four spawning areas have been found for the eastern Atlantic bluefin tuna stock in the Mediterranean Sea, so it is not implausible that there is more than one spawning area in the Gulf of Mexico for the western Atlantic bluefin tuna stock. The individuals used in this study were caught as bycatch by the Mexican surface longline fleet between January and April 2015. A total of 63 individuals ranging between 192 and 293 cm LF (mean = 238 ± 22.52 cm) were measured. Gonads from 46 fish (31 females and 15 males) were collected for histological examination. All the individuals were classified as mature; 25 were reproductively active (in spawning capable and spawning stages). The histological analysis indicates spawning activity in Mexican waters (the southern Gulf of Mexico). Spawning occurred in March and April, when the sea surface temperature was 25.57 °C ± 0.69 in March and 27.03 °C ± 0.69 in April. Information on the location of the spawning areas is necessary for a correct management of species. The present study provides the first histological evidence of reproductive activity in Mexican waters, and indicates a wider spawning area, beyond just the northern zone, potentially encompassing the entire Gulf of Mexico.

Elevated mortalities of triploid eastern oysters cultured off-bottom in northern Gulf of Mexico

After unusually high mortalities of eastern oysters (Crassostrea virginica) were reported at commercial farms in Alabama during the summer of 2016, this study was conducted to determine whether the mortalities were reproducible, site-specific, and linked to ploidy. Seed of triploid and diploid oysters were deployed in November 2016 at four sites adjacent to commercial oyster farms in Alabama: Mobile Bay, Navy Cove, Grand Bay, and Dauphin Island. Mortality, growth, condition index, gametogenesis, and Perkinsus marinus infection intensity were monitored until October 2017. Mortalities were significantly greater in triploids by the end of the study, but the magnitude and timing of mortalities differed among sites. Triploids and diploids at Mobile Bay experienced severe mortalities in summer (100% in about two months), and the start of this mortality event was delayed in diploids. Elevated triploid mortalities were observed at Navy Cove (77%) and Dauphin Island (60%) in late spring through fall, while oysters at Grand Bay suffered the lowest triploid mortalities (34%). Possible causes of the high mortalities included environmental conditions, such as prolonged periods of low salinity and high temperature in summer at Mobile Bay, as well as, heavy P. marinus infection intensities in fall at Grand Bay. Despite elevated triploid mortalities, both triploids and diploids showed faster shell height growth at Navy Cove and Dauphin Island. Conversely, the site with minimal triploid mortality had the slowest shell height growth overall, but the greatest difference in shell height between triploids and diploids. Analysis of gametogenic stages and gonad-to-body ratios over the summer revealed diploids primarily in the spawning stage and triploids showing delayed and diminished gametogenesis, with lower gonad-to-body ratios than diploids.

Analysis of the Gynaephora qinghaiensis pupae immune transcriptome in response to parasitization by Thektogaster sp

As a pest on the Qinghai-Tibet Plateau, Gynaephora qinghaiensis causes severe damage to grassland vegetation and its pupae are also natural hosts of Thektogaster sp. To successfully parasitize, endoparasitoids generally introduce or secrete multiple parasitic factors into the host body during the spawning stage to suppress the host immune response. To study the parasitic effects of Thektogaster sp. on G. qinghaiensis, a transcriptome analysis of immune-related genes in parasitized and nonparasitized G. qinghaiensis pupae was performed. A total of 371,260,704 clean reads were assembled into 118,144 unigenes with an average length of 884.33 base pairs. Of these, 23,660 unigenes were annotated in at least one database and 94,484 unigenes were not annotated in any databases. These findings indicated that the majority of the genetic resources (79.97% of all unigenes) in Gynaephora should be further explored. Parasitization significantly affected the transcriptional profile of G. qinghaiensis pupae. The present study identified 12,322 differentially expressed genes and 57 immune-related genes were identified in parasitized G. qinghaiensis pupae. Most immune-related genes were downregulated, potentially resulting from the inhibitory effect of Thektogaster sp. on G. qinghaiensis pupae after parasitization. Overall, the transcriptome analysis sheds valuable light on the molecular mechanisms of G. qinghaiensis parasitization by Thektogaster sp. and promotes the development of novel biocontrol strategies for Gynaephora based on immune defense.

Ciclo reproductivo en dos bancos de Modiolus capax (Bivalvia: Mytilidae) a diferente profundidad en la Ensenada de La Paz, Golfo de California , México

Background. The mussel Modiolus capax is a commercially important resource in the northwest of Mexico; however few studies evaluate its reproduction. Goals. The reproductive activity and the gonadosomatic index of were used to describe the seasonal variations in the reproductive cycle of the M. capax and the relationship with the environmental changes. Methods. Approximately 24 specimens were collected per month in two localities at La Paz inlet, Baja California Sur, Mexico, between October 2008 and December 2010. Relationships between gonad developmental states and size were estimated; also, its relationships with temperature and chlorophyll-a. Results. The results indicated a synchronous spawning between males and females in March in one locality and in January in the other. In both localities, ripe and post-spawning females showed follicular atresia, in up to 82% of all females in one locality. The smallest organisms were found in the early gametogenesis stage; the largest, in the spawning stage. The gonadosomatic index differed between localities, and was positively correlated with the increase in chlorophyll-a. A significant relationship was observed between temperature and the frequencies of the gametogenesis and ripening stages. Conclusions. The study of the reproduction of M. capax revealed that environmental changes affect on the activity and reproductive status and favored the development of follicular atresia.

Reproductive traits and relative gonad expenditure of the sexes of the free spawning Chiton articulatus (Mollusca: Polyplacophora)

ABSTRACTReproductive studies of an intertidal free-spawning population of Chiton articulatus (Mollusca: Polyplacophora) from Puerto Angel, Oaxaca, Mexico were undertaken during 2011. We used gonad histology and gonadal indices to assess the relative gonad expenditure of the sexes (RGES) and other reproductive traits, accounting for individual and seasonal variation within this population. At this location, C. articulatus is gonochoric, without sexual dimorphism, except internally by gonad colour (testis is ‘salmon’ coloured and ovary olive green). Annual and monthly sex ratios (m/f) do not differ significantly from 1:1. Highest population-level gonadosomatic index (GSI) corresponded to maximum (peak) ripe stage (i.e. maximum gonad investment), with a first peak in May with a high value (8.4 ± 0.5) and a second peak during August-September with a lower value (4.7 ± 0.3). GSI fluctuated throughout year implying that gonad expenditure may be seasonally constrained, but with overall synchrony between sexes of ripe and spawning stages. July to December was the main reproductive season with some facultative spawning occurring off-season. Ripe and spawning RGES did not differ between sexes, suggesting that either sperm competition is intense and/or that sperm limitation is high. Early spawning individuals may quickly replenish their gametes for a second phase of gamete release later.Abbreviations: RGES: relative gonad expenditure of the sexes; GSI: gonadosomatic index; GDS: gonad developmental stages; MiMI: microscopic maturity index; SST: sea-surface temperature.

Histological analysis of oogenesis and ovarian development of the freshwater crab Sinopotamon henanense.

The morphological and cytological changes of oogenesis and ovarian development were described in the freshwater crab Sinopotamon henanense through macroscopic and microscopic examinations. Serial histological dissections of the ovaries demonstrated that oocyte development was asynchronous. Oogenesis was divided into four distinct stages including six phases: oogonium stage, the first phase (OI) and the second phase (OII) comprising the previtellogenic stage, the third phase (OIII), the fourth phase (OIV) and the fifth phase (OV), comprising the vitellogenic stage and the sixth phase representing the mature stage. Furthermore, examining and analyzing the gonadosomatic indices showed that the developmental cycle of the ovary was closely related to season, and indicated that the breeding season of S. henanense was between May and June. Ovarian development was classified into six stages: proliferation stage, small growth stage, large growth stage, pre-maturation stage, mature stage and spawning stage. Ovaries varied in size and color during each developmental stage, which were closely related to the status and proportions of oogonia and primary oocytes. Although there were cases that oocytes at two or more phases were present at each stage, ovary developmental stages were substantially different. These results provide an important base for studies of the regulatory mechanisms of oogenesis in this compared to other brachyuran species, and will be useful for the aquaculture of S. henanense and related species.