Asynchronous Ovarian Development Research Articles

Fecundity, Length at First Sexual Maturity and Gonadal Development of Lepidorhombus boscii in the Eastern Adriatic Sea.

This study presents data on the seasonal changes in population structure, maturation, fecundity and reproduction of the Lepidorhombus boscii from the central-eastern Adriatic Sea. This species is a commercially valuable fish in the Adriatic Sea; still, knowledge about its reproductive biology is very scarce. The analyses are based on the data collected between July 2020 and June 2021 by bottom trawls. In total, 963 individuals were collected out of which 508 were females (47.24%) and 455 were males (52.75%). Throughout the year, oocytes in the previtellogenic and vitellogenic stages were present in the ovaries, and the development of the ovaries followed the values of the gonadosomatic index. L. boscii has asynchronous ovarian development and a prolonged spawning season in the Adriatic Sea with the main spawning season between November and March. The oocyte diameter ranged from 34.01 to 562.72 μm (178.49 ± 129.83 μm). This study presents the first information on the reproductive cycle of L. boscii in the eastern Adriatic Sea and contributes to the understanding of the biology of this species necessary for its sustainable management.

Multiple paternity in reproduction of European eel Anguilla anguilla (L. 1758) by artificial mixing of different sperm in equal volumes

Because of its complex life cycle and due to multiple stress factors, the European eel is suffering a dramatic decline and has been declared Critically Endangered by the IUCN. A possible way to address this problem could be relieve the pressure on natural stocks by implementing its mass production by artificial breeding protocols. A previous study based on direct observation and parentage assignment underlined the presence of an allegedly hierarchic structure among European eel males in semi-natural mating conditions, with a consequent bias in F1 proportion assigned to each one. The aim of the present study is to attest if a different fertilization protocol based on the artificial mixing of female eggs with different males’ milt in equal volume (1 F:4 M) could represent a solution to the disproportion observed in semi-natural conditions. For this purpose, six families of European eels were generated, and 10 species-specific microsatellite loci were used to infer offspring composition by paternity assignment on 280 samples. Due to the asynchronous ovarian development of female European eels, the percentage of fertilized eggs for each female showed a great variability, ranging from 4.70% to 94.50%. A proportion of 94.02% of genotyped offspring were assigned with high confidence to their true parents. As regard males’ fertilization pattern, no substantial differences from natural mating were observed: a single male accounted for most offspring, which was just mostly composed of full sibs. Concluding, the obtained results suggest that the admixture of an equal volume of different males’ milt seems to contribute to the single-locus genetic variability (observed heterozygosity higher than expected in 7 out 9 loci), but it is not sufficient to ensure all the males the same chance to transmit their gene pool, and new fertilization strategies must be developed.

Deciphering the Dynamics of Reproduction and Diet for Bigeye Ilisha (Ilisha megaloptera) from the Saurashtra Coast, Northeastern Arabian Sea

Ghosh, S. and Vase, V., 2022. Deciphering the dynamics of reproduction and diet for bigeye ilisha (Ilisha megaloptera) from the Saurashtra coast, northeastern Arabian Sea. Journal of Coastal Research, 38(5), 1050–1060. Coconut Creek (Florida), ISSN 0749-0208. With no exhaustive information available for Ilisha megaloptera, the present study aimed at elucidating the reproductive and feeding dynamics from 764 individuals landed by gillnetters at Veraval, India, in the northeastern Arabian Sea. Standard length ranged from 18.4 cm to 35.2 cm. Growth was isometric in males and negatively allometric in females. Sex ratio (F:M) was 1.22, with significant dominance of females at most size classes. Maturity sizes for females and males were 24.21 cm and 24.92 cm. Observation showed that Ilisha megaloptera spawned throughout the year with major and minor peaks occurring from February to May and November to December, respectively. The monthly percentage contribution of spawning females and males ranged from 16.0 to 72.22 and 22.22 to 73.68, and the gonadosomatic index for females varied between 3.59 and 7.68. Absolute fecundity ranged from 22,875 eggs to 121,013 eggs. Asynchronous ovarian development with three distinct modes in egg distribution indicated multiple spawning events. Feeding intensity was low, with 26.05% exhibiting part-full stomachs and 7.20% full stomachs. Feeding activity was lowest during spawning peaks and highest in fishes measuring 26.0–29.9 cm. Below 22.0 cm, feeding was solely on zooplankton, dominated by copepods. Feeding henceforth was mostly on nekton: crustaceans (39.35%) and teleost juveniles (38.72%). Ontogenetic shifts and seasonal variations in prey signified optimal foraging. Precipitation and salinity significantly impacted the monthly gonadosomatic index and predator–prey weight ratio. The present study provides a detailed report on bionomics for Ilisha megaloptera and could contribute to the management of Ilisha spp. stocks in the Indian Ocean, considering the paucity of information available for other species in this genus.

Reproductive cycle of Calamus brachysomus (Teleostei: Sparidae) in the Central Gulf of California, BCS, Mexico

The Pacific porgy Calamus brachysomus (Lockington, 1880) is exploited for local consumption and commerce in Baja California Sur (BCS). Monthly samples to study its reproductive biology were obtained from the artisanal fishery operating in Santa Rosalía, BCS, Mexico, from July 2015 to July 2016. A total of 265 specimens were analyzed, including 147 females and 118 males. The sexual proportion (1.24F:1M) did not differ from the expected 1:1 proportion (P = 0.08). There were no significant differences between sexes in total length (P = 0.94). Variations in the hepatosomatic index and condition factor indicated that food constituted the main energy source during reproduction, with possible additional use of endogenous reserves originating in the liver during spawning. The gonads histological analysis indicated an asynchronous ovarian development and batch spawning strategy. There were spawning capable females during 11 of the 13 sampled months; the exceptions were February and September, coinciding with minimum and maximum sea surface temperature (SST) values. These results, along with the gonadosomatic index variations, allowed us to conclude that C. brachysomus reproduces over a large part of the year with an activity peak from May to July, in an SST interval of 21 to 28ºC.

First report on the diet and reproductive biology of red-toothed triggerfishOdonus niger(Ruppell, 1836) from the south-eastern Arabian Sea

AbstractThe feeding habits and reproductive biology of red-toothed triggerfishOdonus niger(Ruppell, 1836) was analysed from 449 specimens collected from the Karnataka coast of the south-eastern Arabian Sea. Of the total stomachs examined, only 54 (12%) were empty and 395 contained food remains. The diet comprised crustacean remains (48.0%), zooplankton (21.4%), algae (16.5%), fish remains (6.1%) and cephalopod remains (5.3%) along with partially digested matter (2.3%) and detritus (0.4%). The species was found to be a generalist feeder and an omnivore. The overall sex ratio between males and females (1: 0.44) was significantly (P< 0.05) different. Histological examination of the ovaries indicated asynchronous ovarian development in females, with males maturing earlier than females. The gonadosomatic index (GSI) patterns of males and females, and the presence of ripe ovaries and spermatozoids suggested that April–May is the peak spawning period. The absolute and relative fecundity estimates ranged from 16,464–312,420 eggs and 251–2812 eggs g−1respectively. Fecundity was positively correlated with total length and body weight. The biological information on diet composition and reproductive traits provided for the first time in this study can facilitate conservation, management and sustainable exploitation of this species in the study area.

A first assessment of atresia in the Chilean jack mackerel <i>Trachurus murphyi</i> (Teleostei, Carangidae) from the South-eastern Pacific Ocean

The Chilean jack mackerel Trachurus murphyi support an important fishery in the South-eastern Pacific Ocean and has declined considerably over time. T. murphyi have asynchronous ovarian development with an oceanic spawning (September to January). Despite the economic importance of this resource critical issue such as characteristics and dynamics of atresia, which affect the reproductive output, are unknown. Females of T. murphyi caught in different spawning seasons were analysed to describe patterns of prevalence and intensity of atresia. General linear models (GLM) were performed by using prevalence and intensity atresia as response variables and gonadosomatic index, condition factor, sea surface temperature, postovulatory follicles and month/year as explanatory variables. The batch fecundity and relative fecundity were compared between females showing atresia, postovulatory follicles and non-atretic females. The stages of atresia identified were alpha, beta and gamma. The GLM showed that variations in the prevalence and intensity of atresia were explained for all variables, except condition factor for prevalence, and gonadosomatic index for intensity of atresia. According to our results, the dynamic of alpha and beta atresia could be considered a potential proxy for any disruption of spawning season. The batch fecundity and relative fecundity were lowest compared with other Trachurus spp. This is the first assessment comparing fecundity between atretic and not atretic females for this species.

Contribution to the reproductive ecology of Notoscopelus resplendens (Richardson, 1845) (Myctophidae) in the Central-Eastern Atlantic

Notoscopelus resplendens is an abundant myctophid in the region of the Central-Eastern Atlantic. As with a majority of other myctophid species, this species performs vertical migration, playing a key role in the oceanic food web and in carbon sequestration. We examined the reproductive biology of N. resplendens based on 579 specimens caught between 1997 and 2002 off the Canary Islands. We found that the maximum standard length (SL) was lower than the size reported by other authors. The sex ratio was not different from 1:1. The average size at first maturity (L50) was higher in females (60.34 mm SL) than in males (56.61 mm SL). The gonadosomatic index (GSI) at 50% sexual maturity in females was higher than that in males. The reproductive activity was observed from January to April, while from May onwards, the majority of fish caught were in the process of maturation. The macroscopic scale of maturation was validated through the histological analysis of the ovarian development. The batch fecundity was related to the standard length, with an average of 1068.69 ± 369.84 eggs/spawn. These first data obtained for N. resplendens indicated that it is a batch spawner with asynchronous ovarian development.

Sexual dichromatism and dimorphism in the goatfish Parupeneus spilurus (Perciformes: Mullidae) in southern Japan

Examination of gonads, fresh coloration and external morphology of Parupeneus spilurus (Perciformes: Mullidae), based on 55 males [115.4–315.9 mm SL (mean 254.1 mm)] and 22 females [116.2–299.5 mm SL (225.3 mm)], provided evidence of both sexual dichromatism and dimorphism. Males consistently had six to nine oblique yellow stripes and two yellow stripes on the second dorsal fin and anal fin, respectively. Females less than 212.3 mm SL had a reddish second dorsal fin, becoming yellowish (but no stripes or blotches) with maturity (> 215.4 mm SL). The anal fin of females was usually reddish without yellow stripes, even at full maturity, although a single yellow stripe on the anal fin is likely during breeding periods (at least before ovulation). Whereas the caudal fin of females always lacked yellow markings, these occurred in mature males (> 193.0 mm SL), tending to change from stripes to blotches via broken stripes with subsequent growth. Males differed slightly from females in some relative proportions (orbit diameter, and upper-jaw and anal-fin base lengths). Parupeneus spilurus was found to be a gonochoristic, multiple-spawning species (more than one spawning per year) with asynchronous ovarian development.

Reproductive cycle of Aplodinotus grunniens females (Rafinesque, 1819) in the Usumacinta River, Mexico

The freshwater drum Aplodinotus grunniens is a species widely distributed in North America. In the Mexican southeast, this species occurs in the Usumacinta River, where it supports an artisanal fishery. In this regard, the present study was conducted to supply detailed information on the female reproductive cycle of this species. Calculations of gonadosomatic (GSI) and hepatosomatic (HSI) indexes, histological and visual staging of ovaries as well as the staging of oocyte development were applied together to determine the reproductive changes during an annual cycle. The histological analysis revealed the presence of spawning capable females throughout the year, and the distribution frequencies of oocyte diameters displayed the continuous occurrence of mature oocytes, with great data dispersion and different modal groups. These observations were further corroborated by the presence of alternating peaks and drops in the GSI and HSIs, which were correlated with the occurrence of maturing and spawned females. These data, taken together, reveal that A. grunniens from the Usumacinta River is a partial spawner with asynchronous ovarian development and undetermined fecundity that reproduces year-round, but with spawning occurring preferably during the rainfall-flooding season (June to November). The Usumacinta River seems to be a permanently favorable environment for sheltering, feeding and growth of A. grunniens broods, especially during the flooding season. The information generated in this study will be useful for the development of management strategies in the wild as well as for the exploration of A. grunniens as a potential species for aquaculture production in southern Mexico.

Effects of pituitary extract, ovaprim, and bitter leaf (Vernonia amygdalina) on the histopathology of African catfish (Clarias gariepinus)

The development of aquaculture in Nigeria is constrained by the inadequate supply of high quality of fingerlings of African catfish (Clarias gariepinus). There are conflicting reports on the reproductive efficacy of Vernonia amygdalina when compared with the synthetic hormone Ovaprim (OV) and Pituitary Extract (PE) on C. gariepinus. The histopathology of select organs in catfish treated with generic Ovaprim (OV), Pituitary Extract (CPE), and aqueous extract of Vernonia amygdalina (VAE) were evaluated. Sixteen female C. gariepinus (average weight of 1 kg) wereevenly and randomly distributed to four groups. Fish in groups A, B, C, and D were injected intramuscularly with aqueous solutions of OV (0.5 mL/kg), PE (5 mg/kg), VAE (10 mg/kg), and distilled water (DW; 0.5 ml), respectively. Histological examinations of the ovary, liver, kidney, and spleen were carried out. Histopathology revealed that OV- and PE-treated groups showed synchronous and synchronous ovarian development, vacuolar change of hepatocytes, thinning of hepatic cords, reduced renal haemopoietic compartments, tubular degeneration and necrosis, and decrease in splenic periarteriolar lymphoid sheaths (PALS). VAE-treated groups had asynchronous ovarian development with atretic ovarian follicles, widespread vacuolar change of hepatocytes, intact renal tubular and hemopoietic compartments, and preponderance of large and coalescing splenic PALS. We conclude that VAE is an ineffective spawning agent, especially when compared with OV and PE, as VAE could not induce synchronous gonadal development. However, VAE may have immunopotentiating, nephroprotective, and haemopoietic properties.

The ovarian development, fecundity and hypothesis on spawning pattern of common cuttlefish Sepia officinalis off Mauritania

Cephalopod species have evolved highly flexible spawning strategies, but the extent to which spawning strategy adopted is inextricably linked to the ovarian development. To address the spawning strategy of common cuttlefish Sepia officinalis outside northwest Africa, an analysis of ovarian development and hypothesis on spawning pattern was undertaken for specimens (mantle length of 126–270 mm from stages II to IV) collected from commercial catches off Mauritania during summer months of July and August 2015. It was found that the mature/spawning female S. officinalis covered a wide range of body size, being 148–270 mm ML, and showed non-stop food intake. The gonadosomatic index (GSI) increased steadily with maturity from 2.13% to 13.22%, being higher mean value of 8.65 ± 1.69% at mature/spawning stage. Potential fecundity (PF) increased with female size from 1306 to 3376 oocytes (mean 2327 ± 554.47). The oocytes were developing asynchronously as evidenced by the dominant small oocytes throughout sexual maturation and a bimodal size-frequency distribution of yolk oocytes for animals at maturing and mature/spawning stages. The mature oocytes in ovaries of mature/spawning individuals consistently accounted for less than 1% PF. There were about 770–1966 viable eggs that would be released during the spawning season. These evidences indicate that S. officinalis off Mauritania undergo the asynchronous ovarian development, and adopt a complementary spawning strategy falling somewhere along a continuum between intermittent and multiple spawning to adapt to the nutrient-rich Mauritanian upwelling system.

Dynamics of ovarian maturation throughout the reproductive cycle of the Neotropical cichlid fishCichlasomadimerus(Teleostei, Cichliformes)

In this study, we analyzed gene expression profiles, plasma steroids concentrations, and gonadal morphology throughout the reproductive cycle of female Cichlasoma dimerus (Heckel, 1840), a monogamous cichlid fish exhibiting social hierarchies. Fish were analyzed at six phases encompassing their annual cycle, namely resting (during the nonreproductive period), prespawning, 30 h post spawning, 4 days post spawning, 10 days post spawning, and subordinate (during the reproductive period). The histological and histomorphometric analysis showed that C. dimerus exhibits asynchronous ovarian development. Similar to resting females, subordinate females showed low gonadosomatic index, reduced expression levels of vitellogenin (vtgAb), zona pellucida (zpB), gonadal aromatase (cyp19a1A), and low concentrations of plasma sex steroids, thus indicating that social intimidation by dominant conspecifics elicited reproductive arrest. In reproductively active females, a direct positive correlation between plasma estradiol, vtgAb expression, percentage of late vitellogenic oocytes, and gonadosomatic index was observed. These parameters were maximal at the prespawning phase, decreased at 30 h post spawning and 4 days post spawning, and then reached a peak at 10 days post spawning. Our results indicate that female C. dimerus become spawning capable after 10 days post spawning, coincidently with the shortest time interval between successive spawns recorded in captivity.

Reproductive biology of Pseudotocinclus tietensis (Siluriformes: Loricariidae: Hypoptopomatinae), a threatened fish species

Pseudotocinclus tietensis is endemic to the Upper Tiete River basin and classified as vulnerable. The reproductive biology of this species is still unknown, therefore, we investigated its reproductive strategy and gonad development during its annual reproductive cycle. The fish were collected throughout one year, and histology of the gonads, fecundity and oocyte diameter was conducted. Three phases of gonad maturation were found in males and females (immature, developing, and spawning capable), and the development stages of the gametes were identified within each stage. In the testes, four stages of gamete development were distinguished: spermatogonia, spermatocytes, spermatids and spermatozoa. During spermiation, the spermatozoa were released into the tubular lumen and then continued through the efferent ducts. In the ovaries, five stages of gamete development were identified: chromatin nuclear, perinucleolar, yolk vesicle formation, vitellogenic and ripe. The minimum diameter of ovulating oocytes was 297 µm, and the absolute fecundity was 64 to 306 oocytes. Males with spermatozoa in the lobular lumen and females with vitellogenic and ripe oocytes were found throughout the year. Pseudotocinclus tietensis has asynchronous ovarian development and gametes with fertilization capacity can be eliminated throughout the annual cycle.

Gonadotropin subunits of the characiform Astyanax altiparanae: Molecular characterization, spatiotemporal expression and their possible role on female reproductive dysfunction in captivity

To better understand the endocrine control of reproduction in Characiformes and the reproductive dysfunctions that commonly occur in migratory fish of this order when kept in captivity, we chose Astyanax altiparanae, which has asynchronous ovarian development and multiple spawning events, as model species. From A. altiparanae pituitary total RNA, we cloned the full-length cDNAs coding for the follicle-stimulating hormone β subunit (fshb), the luteinizing hormone β subunit (lhb), and the common gonadotropin α subunit (gpha). All three sequences showed the highest degree of amino acid identity with other homologous sequences from Siluriformes and Cypriniformes. Real-time, quantitative PCR analysis showed that gpha, fshb and lhb mRNAs were restricted to the pituitary gland. In situ hybridization and immunofluorescence, using specific-developed and characterized polyclonal antibodies, revealed that both gonadotropin β subunits mRNAs/proteins are expressed by distinct populations of gonadotropic cells in the proximal pars distalis. No marked variations for lhb transcripts levels were detected during the reproductive cycle, and 17α,20β-dihydroxy-4-pregnen-3-one plasma levels were also constant, suggesting that the reproductive dysfunction seen in A. altiparanae females in captivity are probably due to a lack of increase of Lh synthesis during spawning season. In contrast, fshb transcripts changed significantly during the reproductive cycle, although estradiol-17β (E2) levels remained constant during the experiment, possibly due to a differential regulation of E2 synthesis. Taken together, these data demonstrate the putative involvement of gonadotropin signaling on the impairment of the reproductive function in a migratory species when kept in captivity. Future experimental studies must be carried to clarify this hypothesis. All these data open the possibility for further basic and applied studies related to reproduction in this fish model.

Gonadotropin characterization, localization and expression in the European hake (Merluccius merluccius)

In vertebrates, the regulation of gametogenesis is under the control of gonadotropins (Gth), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh). In fish, the physiological role of Gths is not fully understood, especially in species with asynchronous ovarian development. To elucidate the role of Gths in species with asynchronous ovary, we studied European hake (Merluccius merluccius) during the reproductive season. For this aim, we first cloned and sequenced both hormones. Then, we characterized their amino acid sequence and performed phylogenetic analyses to verify the relationship to their orthologues in other species. In addition, the quantification of gene expression during their natural reproductive season was analyzed in wild-caught female hake. Our results revealed that fshb peaked during the vitellogenic phase, remaining high until spawning. This is in contrast to the situation in species with synchronous ovary. lhb, on the other hand, peaked during maturation as it is also common in species with synchronous ovarian development. Finally, combining double-labeling fluorescent in situ hybridization (FISH) for Gth mRNAs with immunofluorescence for Lh protein, we evidenced the specific expression of fshb and lhb in different cells within the proximal pars distalis (PPD) of the pituitary. In addition to gonadotrope cells specific to expression of either fshb or lhb, some cells showed co-expression of both genes. This suggests either that gonadotropes with co-expression are not yet specified or they could have a plasticity that permits changes from one cell phenotype to another during certain life stages and in turn during different physiological states.

Integrated application of transcriptomics and metabolomics yields insights into population-asynchronous ovary development in Coilia nasus.

Populations of Coilia nasus demonstrate asynchronous ovarian development, which severely restricts artificial breeding and large-scale cultivation. In this study, we used a combination of transcriptomic and metabolomic methods to identify the key signaling pathways and genes regulation affecting ovarian development. We identified 565 compounds and generated 47,049 unigenes from ovary tissue. Fifteen metabolites and 830 genes were significantly up-regulated, while 27 metabolites and 642 genes were significantly down-regulated from stage III to stage IV of ovary development. Meanwhile, 31 metabolites and 1,932 genes were significantly up-regulated, and four metabolites and 764 genes were down-regulated from stage IV to stage V. These differentially expressed genes and metabolites were enriched by MetScape. Forty-three and 50 signaling pathways had important functions from stage III–IV and from stage IV–V in the ovary, respectively. Among the above signaling pathways, 39 played important roles from ovarian stage III–V, including “squalene and cholesterol biosynthesis”, “steroid hormone biosynthesis”, and “arachidonate metabolism and prostaglandin formation” pathways which may thus have key roles in regulating asynchronous development. These results shed new light on our understanding of the mechanisms responsible for population-asynchronous development in fish.

Identification and characterization of a progestin and adipoQ receptor (PAQR) structurally related to Paqr7 in the ovary of Cynoglossus semilaevis and its potential role in regulating oocyte maturation

Membrane progestin receptors (mPRs) play an important role in the regulation of oocyte meiotic maturation in fish. However, details of the molecular endocrine mechanism regulating oocyte maturation in multiple spawning fish with asynchronous ovarian development remain unclear. The cDNA encoding a novel progestin and adipoQ receptor with structural similarity to mPRα (Paqr7), herein called Paqr7b, was cloned and sequenced from the ovary of half-smooth tongue sole Cynoglossus semilaevis. Phylogenetic analysis showed that Paqr7b represents an evolutionary intermediate between mPRα and mPRβ and shares high homology with other similar Paqr proteins in other teleost species. However, the tongue sole Paqr7b protein showed much greater homology to teleost mPRαs (average 52%) than mPRβs (average 40%), suggesting it may have arisen from gene duplication of mPRα. paqr7b and paqr7 mRNA exhibited similar patterns of tissue expression. The mRNA and protein of Paqr7b were ubiquitously detected in all tissues analyzed, including the ovary. Moreover, in situ hybridization results revealed that paqr7b was expressed in stage V oocytes, as well as in scattered cells in the pituitary. The expression of paqr7b mRNA in brain and ovary significantly increased from ovarian development stage II to stage V (P<0.05), and was maximal at stage V, and then sharply decreased at stage VI. The transcript level of paqr7b mRNA in the pituitary also peaked at stage V (P<0.05). Treatment of tongue sole ovarian follicles with gonadotropin consistently increased the expression level of Paqr7b protein and mRNA in both a dose- and stage-dependent manner. Microinjection of tongue sole oocytes with a morpholino antisense oligonucleotide to Paqr7b blocked the progestin induction of oocyte maturation. Our findings demonstrate an important role of Paqr7b in the regulation of oocyte maturation in tongue sole and suggest the receptor may also influence other aspects of reproduction, such as pituitary function.

Endocrine changes during the previtellogenic stage of the great sturgeon, Huso huso (Linnaeus, 1758)

The study aimed to investigate changes in serum concentrations of sex steroids, thyroid hormones, stress indices, cholesterol, triacylglycerol, calcium and phosphorus, as well as the growth in the 3-year old previtellogenic stage of great sturgeon, Huso huso over a 6-month period. Forty individually marked fish (mean weight 6913 g) were divided among three circular tanks under a natural temperature and photoperiod. Every 1.5 months fish were weighed and blood samples taken for serum analysis. Fish showed significant changes in 17β estradiol, testosterone, triiodothyronine (T3), thyroxine (T4), adrenocorticotropic hormone, cortisol, cholesterol, and phosphorus, but not in triacylglycerol and calcium concentrations. From the January onset of the experiment to the end of the trial in July, there was a decrease in sex steroids and cortisol concentrations as well as a decline in T3 concentrations from March and in T4 from February to July. The mean weight of fish increased significantly from the beginning to the end of the experiment. Although the oocyte diameter increased from 197 to 202 μm, the difference was not significant. The histological data on oocytes suggest that the great sturgeon, like the other sturgeons, has a heterogeneous asynchronous ovarian development in the early stage of reproduction. This data might be useful to the further understanding of the physiology of Huso huso and/or to improve its culture. Moreover, it leads to a general increase in the understanding of the basic reproductive biology of this valuable chondrostean species.

Molecular and transcriptional characterization of GTHs and mPRα during ovarian maturation in rock bream Oplegnathus fasciatus.

The membrane progestin receptor α (mPRα) plays an important role in the regulation of oocyte meiotic maturation in fish. However, the endocrine regulation of multiple spawning in fish with asynchronous ovarian development remains to be determined. We identified four genes (FSHβ, LHβ, CGα and mPRα) that are widely expressed in both the reproductive and non-reproductive tissues of rock bream Oplegnathus fasciatus and examined their expression during ovarian maturation. The level of FSHβ transcripts in the pituitary remained high during vitellogenic stages, when the plasma levels of estradiol-17β reached maximum levels and oocyte development was stimulated. LHβ expression in the pituitary and ovary reached maximum levels during oocyte maturation when the plasma levels of testosterone also reached a maximum. A significant correlation between mPRα transcript levels and the gonadosomatic index was observed during vitellogenesis and final maturation. Brain gonadotropin (FSHβ and LHβ) and mPRα were continuously expressed at different stages of ovarian development. The dynamic and diverse nature of gonadotropins and mPRα gene expression patterns suggests that these genes might jointly regulate ovarian development and maturation through the brain-pituitary-ovary axis in the rock bream endocrine system.

Reproductive biology of the yellow snapper, Lutjanus argentiventris (Pisces, Lutjanidae), from the Mexican central Pacific

The yellow snapper, Lutjanus argentiventris, is a commercial species along the Pacific coast, yet few studies have been carried out on its reproductive biology. Monthly samplings of the artisanal fishery off the coast of Jalisco, Mexico, were made from 1998 to 2008. Mean total length and weight of analyzed specimens were 32.6 cm (±0.13) and 567.3 g (±9.15), respectively. A total of 945 females (50.3%) and 932 males (49.7%) were collected; the overall sex ratio was 1:0.99. The highest percentages of mature fish were obtained between July and October. The highest gonadosomatic index values (1.46 to 0.81) and highest oocyte diameters were also obtained during that period. For this reason the period from July to October is considered the breeding season of L. argentiventris. This species presented asynchronous ovarian development and seven stages of oocyte development were identified. The testis showed lobular development and in the ripe stage, sperm were observed in the center of the lobes and in the main duct. Mean size at sexual maturity (L50) was 31.6 cm for females and 31.4 cm for males, and there was no significant variation in L50 among years. Due to the long period of study, this information could be used to establish measures for the proper exploitation of the species.