External Sexual Dimorphism Research Articles

Gametogenesis and weight change of body organs of the sea cucumber Holothuria (Halodeima) grisea (Aspidochirotida: Holothuriidae) in Southern Brazil

The sea cucumber Holothuria (Halodeima) grisea is a widely distributed and economically important species that has been harvested in Brazil for several years, where there are no studies on its reproduction. We studied a population near Guaratuba Bay in Southern Brazil. Four sampling campaigns were made, in February, April, June and October 2008. We examined the macroscopic and microscopic features of the gonads to describe the gametogenesis. In addition, we analyzed the weight change of body organs. A total of 94 individuals were examined and no evidence of external sexual dimorphism was found. In April there were more males than females. Biometrically the body wall and gonads are the most important organs. The body wall increases in the June and the gonads during October and February; there might be an exchange of energy between these organs. Mature gonads are elongated and thick (red in females, cream in males). There were mature individuals year round, with an increase of sexual activity in February when oocyte mature diameter ranges from 70 to 160 µm. Spawning was in winter (June). Maturation period and body component variations were similar between sexes.

The gametogenic cycle and life history ofNicolea uspiana(Polychaeta: Terebellidae) on the south-east coast of Brazil

The gametogenic cycle and life history ofNicolea uspiana(Nogueira, 2003) (Polychaeta: Terebellidae) was studied by taking monthly samples over a 13 month period. Each month, 10 females were sorted; 50 oocytes were removed from the coelom of each specimen, and the maximum diameter was determined. Additionally, 10 males were sorted and 100 gametes were randomly selected from each specimen to evaluate their shape and maturation stage. This species is gonochoric and exhibits slight external sexual dimorphism (in the shape of the nephridial papillae). The sex-ratio ofN. uspianawas 2.4 male for each female. The initial gametic stages of both sexes are produced in special structures called nephromixia. Oogenesis is extra-ovarian, and the germ cells are clumped and surrounded by follicle cells. These cells are ovulated into the coelomic fluid, and yolk synthesis occurs in this cavity. The maximum diameter of oocytes measured, 225 µm, showed that these eggs fall into the size-range for lecithotrophy. Furthermore,N. uspianais an iteroparous species, as the mature individuals can breed several times during their lifetime. Male gonads release germ cells early in development, and sperm maturation also occurs in the coelomic fluid. The male gametes consist of flattened plaques of germ cells attached on their anterior part by a cytophore assuming a rosette-like appearance. Following maturation of the male cells, the spermatids produce arrays of stiffly vibratile tails, assuming a morula shape. The reproductive patterns and life history of the terebellids are also discussed.

Natural history of Copionodon pecten, an endemic trichomycterid catfish from Chapada Diamantina in northeastern Brazil

The natural history of Copionodon pecten was studied based on observations of individuals inhabiting the Coisa Boa River in the Paraguaçu Basin, Chapada Diamantina, Bahia State, Brazil. This catfish is mainly benthonic and dwells in pools beneath riffles, over rocky substrates. Periods of activity, spatial distribution, foraging strategy and diet show variation according to ontogenetic stage, together with variation in external morphological characteristics. Small juveniles are diurnally active, swim mainly in the water column near the border of shallow pools and feed mainly on algae (Spirogyra sp.). Sub-adults and adults of C. pecten are strongly active at night, occupy the bottom of shallow pools and feed mainly on a complex of periphytic algae scratched from the substrate. Dissected specimens have a long digestive tract, which is in accordance with a predominantly algivorous diet. Immature aquatic insects constitute an important food item throughout the life of the fish. Small individuals are gregarious at night, whereas adults congregate especially during the day. When less active, these catfish are observed usually in polarized groups facing upstream. Adult individuals are apparently more numerous than juveniles within the studied population. No distinct reproductive season was recorded for C. pecten during the study, with mature individuals present throughout the year. Oocytes in various stages of development were observed within ovaries, suggesting multiple spawning over a long reproductive period. The species has low fecundity and does not show parental care or external sexual dimorphism. No evidence for a complex behavioural repertoire was found and medium- to large-sized specimens have a tendency to occupy deeper and more sheltered places.

Sex identification and sexual maturity stages in farmed great sturgeon, Huso huso L. through biopsy

Summary Since sturgeons have no external sexual dimorphism and there are no external markers to determine sex, internal examination of the gonads should be used to sex identification. The present study describes the biopsy method and histological observations of the gonads of great sturgeon (Huso huso) in both sexes at different age classes. Sex and maturity stages of 226 great sturgeons were identified through gonadal biopsy and histological observations. A 20-25 mm incision was made with a sharp scalpel through the ventral midline between pectoral and pelvic fins, that allowed gonads to be viewed. Determination of sex and maturity stage was successfully performed in all fish. The sex ratio under culture conditions was 1:0.84 (female: male). Most males and females were at mid-spermatogenesis and pre-vitellogenesis stages, respectively. No apparent mortality and infection was observed after surgery and gonad biopsy in fish. Results of this study showed that sex could be identified by this method when fish are 3-year-old or more. Therefore, biopsy technique is a simple and cost-effective tool in sturgeons and has an important role in aquaculture management and conservation benefits.

Bulked segregant analysis of the pirarucu (Arapaima gigas) genome for identification of sex-specific molecular markers

Arapaima gigas (Osteoglossidae) is one of the largest fish species in the Amazon Basin, attaining lengths of over 2.5 m and weights of over 100 kg. Its flesh is prized, and it has great potential for production in aquaculture systems. However, live pirarucu cannot be reliably sexed visually, even after sexual development, since this species does not have clear external sexual dimorphism. Simple and inexpensive methods for sexing immature pirarucu based on DNA markers would facilitate production of this species in commercial operations. We analyzed A. gigas male and female DNA pools with 566 RAPD primers, generating 2609 fragments, with an estimated 1341 segregating polymorphic markers, and an estimated average spacing of 714 kb, which corresponds to less than 0.1% of the species' genome. Two putative sex-specific fragments were initially identified in bulked samples; but they were not confirmed in a study of individual male and female samples. We suggest that A. gigas has developed a non-chromosomal system of sex determination or, alternatively, that the species has undergone a recent loss of the chromosome carrying the sex-determining locus.

Morphology of Vipera palaestinae : Intraspecific Variability and Sexual Dimorphism

I present new data on intraspecific variations in external morphology and sexual dimorphism in different characteristics of Vipers, Vipera palaestinae in Israel. Corporal proportions and scalation pattern of museum specimens of this snake, the most common viperid species in Israel, were recorded and analyzed. Strong sexual dimorphism was found in tail measurements (its relative length, and number of subcaudal scales), head proportions and in the number of ventral scales. The sexual differences were evident in the head scalation – females have significantly more supralabial and sublabial scales; males, in turn exceed females in circumorbital scale counts. There is no sexual size dimorphism (SSD) in average body weight, snout-vent and total length. The sexes display a similar allometry between SVL/head and SVL/tail length; between tail length and the number of subcaudal scales (weak, but significant relationship). There is no correlation between SVL and the number of ventral or dorsal scales. The morphological plasticity caused by reproduction requirements is well registered and was evident in relating to tail measurements and body scalation, although the possible causes and selective forces of the pholidosis intersexual distinctions can be cleared up through future ecological studies.

Robust molecular sex identification of beaver (Castor canadensis) from non-destructive samples

Beaver (Castor canadensis) are currently the focus of many wetland restoration projects as a keystone species and an ecosystem engineer. This species forms multi-season pair bonds, making sex ratio an especially important consideration for restoration projects. However, beavers lack external sexual dimorphism (with the exception of lactation) and current methods of sex identification have error rates ≥10%. We improved on previous methods of genetic sex identification for beaver by developing a test that uses a short nuclear fragment in addition to an established Y chromosome-specific sex-determining region (SRY) marker. This method had 100% accuracy with 28 known-sex samples and 95% PCR success with no inconsistencies for 42 hair samples from beavers of unknown sex. We used this test to inform a beaver restoration study and increase the probability of population establishment from translocated animals.

Evolution of the light organ system in ponyfishes (Teleostei: Leiognathidae)

Members of the leiognathid subfamily Gazzinae, comprising approximately two-thirds of ponyfish species, are sexually dimorphic with regard to features of the light organ system (LOS). In Gazzinae, the circumesophageal light organ (LO) of males is enlarged and varies in shape compared with similarly sized conspecific females. In association with male species-specific translucent external patches on the head and flank, these sexually dimorphic LO features are hypothesized to be correlated with species-specific luminescence displays. Anatomical differences in LO shape, volume, and orientation, and its association with the gas bladder and other internal structures that function in light emission, are compared to observations of luminescence displays for every major lineage within Leiognathidae. We reconstruct the character evolution of both internal and external morphological features of the LOS to investigate the evolution of LO sexual dimorphism and morphology. Both internal and external sexual dimorphism in the ponyfish LOs were recovered as most likely to have evolved in the common ancestor of Leiognathidae, and likelihood-based correlation analyses indicate that the evolution of internal and external dimorphism in males is statistically correlated. Magnetic resonance imaging technology was applied to examine the unique internal LOs of ponyfishes in situ, which provides a new metric (LO index) for comparison of LO structure across lineages.

Reproductive cycle and size at first sexual maturity of Hexaplex trunculus (Gastropoda: Muricidae) in the Gulf of Gabès (southern Tunisia)

The reproductive cycle and size at first sexual maturity of the banded murex (Hexaplex trunculus) from the tidal areas of the Gulf of Gabès (southern Tunisia) were investigated from June 2007 to May 2008 through macroscopic analysis of the gonads and monthly variations in the general condition (K) and gonadosomatic indices (GSI). This muricid gastropod is gonochoristic (separate sexes throughout life) and lacks external sexual dimorphism. The overall sex-ratio of the population was significantly unbalanced, with a predominance of females (M:F = 1:1.6). The monthly variation in the gonad maturation stages, K and GSI revealed that H. trunculus has a yearly reproductive cycle, with both sexes showing a long period of gonadal activity and slightly asynchronous gametogenic cycle. Gametogenesis occurred during most of the year (11 out of 12 months examined) and almost every gametogenic stage was observed throughout the study period. Ripe males were found mainly from November to January, preceding the main period of gametic emission (between January and May). Ripe females occurred mainly from February to April, preceding the main spawning season (between April and May), apparently triggered by the increasing daylength and seawater temperature during this period (from 13.2 to 14.2 h and from 19.3 to 23.4°C, respectively). Both sexes displayed a relatively short resting phase (males: June—July; females: June—September), coincident with the highest daylength and seawater temperature during summer in the Gulf of Gabès. The first sexual maturity was reached at a smaller size in males (SL50 = 36.9 mm SL) than in females (SL50 = 50 50 40.3 mm SL). The information gathered in this study allowed preliminary management measures for the fishery to be proposed, including a closed season during the main spawning season (April—May) and the establishment of a minimum landing size (of at least 40 mm SL) for H. trunculus from the Gulf of Gabès.

Reproductive Seasonality and Oviposition Induction inTrophon geversianus(Gastropoda: Muricidae) from Golfo Nuevo, Argentina

The reproductive biology of a population of the edible muricid Trophon geversianus inhabiting an intertidal rocky shore in Golfo Nuevo (Chubut, Argentina) was studied regarding the seasonality of oviposition and oviposition induction under laboratory conditions. Sex ratio in the population differed from 1:1 (female biased). The mean shell length was 22 mm for males and 24 mm for females, although the females presented significantly larger maximum sizes. No external sexual dimorphism was evident, whereas the female snails differed internally by the presence of the albumin and capsule gland and by gonad color. Although the population under study inhabits an area with marine traffic and a concentration of 1.9 ng Sn/g, it did not present signs of imposex, in contrast with other sympatric species. T. geversianus presented a marked reproductive seasonality during the study period. Oviposition started in May and concluded in November, when hatching of crawling embryos was registered up to January. This seasonality coincided with changes in water surface temperature, ambient temperature, and photoperiod. Reproductive activities were registered when the environmental stress was minimum. In the aquarium, each female laid an average of 12 egg capsules (range, 6-26) per oviposition event, and needed a total of 25 h (range,12-57 h) to complete attachment of a single egg capsule. Data presented here could be useful for culture of the species.

Reproductive characteristics ofCalyptogena gallardoi(Bivalvia: Vesicomyidae) from a methane seep area off Concepción, Chile

Calyptogena gallardoiis a vesicomyid bivalve inhabiting a methane seep area located at a depth of 740–870 m off the Bay of Concepción, Chile. Vesicomyids host chemoautotrophic sulphide-oxidizing endosymbiont bacteria and are always found associated to reducing environments. In this study, the gonadal structure and the gametes produced byC. gallardoiare described. Light microscopy is used to examine serial histological sections of the gonads, and scanning electron microscopy is used to visualize the external morphology of gametes. The gonads of both males and females are organized in ramified tubular acini. In males, mature sperm are stored near genital openings in acini lined with a secretor epithelium that resembles a seminal receptacle. Spermatozoids have bullet-like heads with an average length of 30.3±2.6 μm (mean±1 SD). In females, the mature oocytes are driven toward the genital opening through evacuator conduits lined by ‘paddle’ cilia. The average diameter of oogonias is 11.6±2.5 μm and that of mature oocytes is 273.8±23.1 μm, making the size of the mature oocyte among the largest reported for bivalves. In addition,C. gallardoiis shown to have external sexual dimorphism. Shells of males are significantly smaller and more elongated with sloping postero-dorsal margin compared with shells of females. The data are discussed in the context of available information on reproductive biology of vesicomyids.

Reproductive biology of the sea cucumber Parastichopus parvimensis (Echinodermata: Holothuroidea) at Isla Natividad and Bahía Tortugas, Baja California Sur, Mexico

The reproduction of the sea cucumber Parastichopus parvimensis was studied from April 2000 to August 2001 at Isla Natividad and from March 2003 to March 2004 at Bahía Tortugas, Baja California Sur, Mexico. Samples were collected manually by semi-autonomous diving. The sea cucumber is a dioecious species, without external sexual dimorphism, with ramified gonad. The development of the gonad confirmed five stages: undifferentiated, gametogenesis, ripe, spawning, and postspawning; this indicated annual synchronous reproduction in both study areas. The sex ratio was 1:1. The variation of the gonadosomatic index was directly related to the gonadal development. Maximum maturity and spawning were recorded from February to May at both sites. The weight at first maturity was 140 g at Isla Natividad and 120 g at Bahía Tortugas. In both areas P. parvimensis showed seasonal visceral atrophy from August to October. As a fishery management alternative, we propose one closed season from February to May to protect the reproductive season (ripe/spawning), and another from August to October to protect the period when the internal organs are absent or atrophied.

Early Development of the Sacramento Perch

AbstractPopulations of the Sacramento perch Archoplites interruptus, California's only native centrarchid, are declining and early development of this imperiled species is poorly known. Therefore, the main objective of this study was to describe the early development of Sacramento perch from fertilization to initiation of exogenous feeding. Embryos were obtained in the laboratory by spawning induction via photoperiod‐temperature control or gonadotropin‐releasing hormone analog treatment. Gross morphology and histological analyses were integrated to describe the early development. Cleavage was synchronous until the 64‐cell stage, which allowed us to calculate the duration of one mitotic cycle during early synchronous cleavage (τ0) as 10–16 min at 25.4–25.6°C. A description of histological events from time to morulation, gastrulation, hatch, and exogenous feeding larvae is provided. Yolk sac larvae tended to adhere to the spawning substrate or sediment during the critical organogenesis stages. Larvae swam up and began exogenous feeding within 4 d postfertilization. Primordial germ cells were observed in 10‐d‐old larvae, but sex differentiation occurred after 43 d. External sexual dimorphism was not observed in early life stages.

A new species of Chondrostoma Agassiz, 1832 (Cypriniformes: Cyprinidae) with sexual dimorphism from the lower Rio Tejo Basin, Portugal

Chondrostoma olisiponensis sp. nov. is described from the lower Rio Tejo Basin. It is a small species (all specimens examined less than 105mm SL) distinguished from the other species of Chondrostoma s.l. by the following combination of characters. Chondrostoma olisiponensis lacks a horny blade on the lower jaw, has a pronouncedly arched mouth, and lacks an intense reddish coloration at the base of the fins. It has elongated pelvic fins that reach the anus and often pass the anal-fin insertion in males, and dorsal, pelvic and anal fins usually have 8 branched rays. The new species has 36 to 43 scales in the lateral line, 7.0 to 8.5 scales above the lateral line, 13 to 16 circumpeduncular scales, denticulated (vs. smooth) grinding teeth surfaces, 6-5/5 pharyngeal teeth and 15 to 19 gill rakers. Chondrostoma olisiponensis is further distinguished from C. lusitanicum, a phylogenetically close species that lives in the same area, by having a higher body, a relatively longer head, and a larger eye. The origins of anal and pelvic fins are displaced anteriorly, while the origin of pectoral fins is displaced posteriorly. Pelvic and pectoral fins and last anal-fin ray are longer in the new species. Unlike the other species in the genus, C. olisiponensis shows external sexual dimorphism, with males having longer pelvic fins whose extremities pass the anus and often overlap with the anal fin. This description raises concerns on the recently proposed splitting of Chondrostoma s.l. since the morphological traits deemed characteristic of some genera are unsuitable for their diagnosis. The species should be considered Critically Endangered (CR) according to IUCN criteria B1ab(ii,iii,iv)c(iv)+2ab(ii,iii,iv)c(iv).

Use of endoscopy for gender and ovarian stage determinations in Russian sturgeon ( Acipenser gueldenstaedtii) grown in aquaculture

The Russian sturgeon ( Acipenser gueldenstaedtii) is native to the Caspian Sea, the Black Sea and the Azov Sea. It used to breed in the main incoming rivers, until dam construction in the mid 20th century blocked upriver spawning migration. Aquaculture of Russian sturgeon has only recently begun, prompted by their declining populations in natural habitats and the rise in meat and caviar prices. However, information on their gonadal development and puberty under culture conditions is incomplete. Because sturgeons have no external sexual dimorphism and there are no external markers for sexing, internal examination of the gonads must be employed for gender identification as well as to monitor their development. The present study describes endoscopic and histological observations of the gonads of young Russian sturgeons aimed at identifying gender and monitoring ovarian developmental stage in females up to the age of 6 years, when they enter their first puberty cycle, as well as at 7 years of age, when they have completed vitellogenesis, under culture conditions. This information, as related to fish age and size, is of vital importance to commercial farming of Russian sturgeon for caviar production and reproduction. For gonadal observations in both sexes, we used an endoscopic system consisting of a 4 mm, 14 cm long cystoscope sheath incorporated with fiber-optic light transmission, connected to a halogen cold light source and a miniature videocamera with a control unit attached to a color monitor. This system allowed us viewing of the fish's abdominal organs, and to save pictures of selected areas of the gonads on a computer as the fish's personal record. Ovarian biopsies were taken in parallel for histology at typical stages of gonadal development. Gender could be identified with this system as early as at 3 years of age and the sex ratio under culture conditions of females, males and unidentified gender were 55, 40 and 5%, respectively. Not only did large differences occur in the developmental stages of female of the same age group, but also ovarian development was highly asynchronous at the early vitellogenic stages. In late vitellogenesis, at the “gray egg” stage (1600–2600 μm diameter), the oocytes were quite regular in size and color, and remained so until the final stages of maturity. Our study suggests that endoscopy is an efficient method for both gender identification at an early age, and for determination of gonadal development stage in sturgeon aquaculture. The ability to see the whole intact gonads of anesthetized fish can reveal important management and research information, with minimal damage or stress to the fish.

Sex ratios of juvenile loggerhead sea turtles Caretta caretta in the Mediterranean Sea

Species with environmental sex determination may have sex ratios different from 1:1, and so sex ratio is an important variable in studies on the population dynamics of these species. This is particularly important for the endangered sea turtles, in order to understand the possible effects of human impacts and conservation measures. Unfortunately, only adults show an evident external sexual dimorphism, so that sex ratio data are difficult to obtain and are limited for the juvenile class, which represents the largest part of a population. Here we present the first extensive assessment of sex ratio of juvenile loggerhead turtles (Caretta caretta) in the Mediterranean Sea. A total of 310 dead turtles from four different areas were sexed by direct examination of gonads, the most reliable sexing method. Females were 54.2% of the whole sample, and no significant differences were found between the study areas. However, this value cannot be ascribed to a single population, because specimens from different nesting sites, both within and outside the Mediterranean, share the same foraging areas and each population may potentially contribute with a different sex ratio. Although we found an unbiased sex ratio, when other information from the region about distribution, mixed stocks, and sex ratios are considered, actually present results are compatible with a hypothetical scenario in which a majority of females are produced in the Mediterranean nesting beaches.

Development of indices for nonsacrificial sexing of imposex-affected Hexaplex (Trunculariopsis) Trunculus (Gastropoda: Muricidae)

The muricid Hexaplex (Trunculariopsis) trunculus lacks external sexual dimorphism and is highly affected by imposex, which further complicates its sexual identification. In this context, the aim of this study was to develop sexual indices based on the dimensions of male and imposex-affected female penis, which could constitute a useful, simple and nonsacrificial tool for sexing live specimens of T. trunculus. The adoption of sexual indices consisting of penis dimensions of both sexes relative to individual size revealed a high accuracy in the sexual identification of sacrificed specimens (.95% correct sexing). Additionally, multivariate discriminant analysis allowed correct sexing of 98.8% of the original 1053 sacrificed individuals, with accurate sexual identification being higher for males (99.5%) than for imposexaffected females (97.7%). An anaesthetization experiment was performed to investigate the effects produced by the anaesthetic (MgCl2) on penis measurements, to test this nonsacrificial approach and to validate the previously developed sexual indices. The anaesthetic provoked an expected enlargement in penis dimensions but, despite this side effect, the sexual indices developed for sacrificed specimens were still highly successful in sexing anaesthetized T. trunculus (generally more than 95% correct sexual identification). The practical application and some limitations of developing and employing this kind of index for the sexual identification of T. trunculus and other imposex-affected gastropod species are discussed.

The reproductive biology of Amathys lutzi, an ampharetid polychaete from hydrothermal vents on the Mid‐Atlantic Ridge

Abstract. The reproductive biology of polychaetes includes a diverse array of characteristics that sometimes have been related to features of the habitat and others times appear to be phylogenetically constrained. The reproductive biology of polychaetes from deep‐sea hydrothermal vents is of particular interest, given the continuing supply of food when vents are active and the ephemeral nature of the vent environment. As part of a survey of reproductive attributes of vent polychaetes, we undertook a descriptive study of the anatomy of the ampharetid polychaete, Amathys lutzi, which lives in mucus‐lined tubes attached to mussel shells or rocks at hydrothermal vent sites along the Mid‐Atlantic Ridge. Reproductive features of ampharetids from the Logatchev vent site were examined with serial sections under light microscopy and with transmission electron microscopy. Members of A. lutzi are gonochoric and lack external sexual dimorphism. Gonads are associated with 3 pairs of mixonephridia found laterally in the anterior region of the polychaete. Oocytes undergo extraovarian oogenesis and are released into the coelom in the previtellogenic phase. Maximum oocyte diameter is∼190 μm, suggesting lecithotrophic development. Within individual females, oocyte size‐frequencies suggest the presence of cohorts of maturing oocytes, consistent with periodic release of gametes. There is no evidence for sperm storage in females. Early stages of developing sperm are also found in the coelom; mature sperm fit the general description of ect‐aquasperm. These reproductive characteristics of individuals of A. lutzi are similar to those of the Pacific vent ampharetid, Amphisamytha galapagensis.

A Clade of Non-Sexually Dimorphic Ponyfishes (Teleostei: Perciformes: Leiognathidae): Phylogeny, Taxonomy, and Description of a New Species

A phylogeny was generated for Leiognathidae, commonly known as ponyfishes, using nucleotide characters from two mitochondrial genes. Results indicate that Leiognathidae comprises two major clades, one consisting of species that exhibit internally sexually dimorphic light-organ systems (LOS), and the Leiognathus equulus species complex, whose members exhibit neither internal nor external sexual dimorphism of the LOS. Species with internally sexually dimorphic LOS generally also exhibit associated male-specific external modifications in the form of transparent patches on the margin of the opercle, the midlateral flank, or behind the pectoral fin axil. The L. equulus species complex is the sister group to all other leiognathids, and a new species, L. robustus, recovered within this clade is described herein. Results demonstrate that Leiognathus is paraphyletic, whereas Gazza and Secutor are each monophyletic and are nested within the sexually dimorphic clade. The morphology of the LOS of non-sexually dimorphic leiognathids is compared to the more common sexually dimorphic state, and differences in these systems are discussed and illustrated. In the context of a family-level phylogeny, we can trace the evolution of the leiognathid LOS from a “simple” non-sexually dimorphic circumesophageal light organ to a complex and species-specific luminescence system involving not only major structural modifications of the light organ itself but also numerous associated tissues.

Gonadal Development and Sexual Dimorphism of Gobiomorus dormitor from the Estuarine System of Tecolutla, Veracruz, Mexico

The bigmouth sleeper, Gobiomorus dormitor, is a benthic, euryhaline species, and is very abundant in river mouths, coastal lagoons, and sites away from marine influence from south Florida to Dutch Guyana. There are few studies of its life history, ecology, and abundance, particularly within Mexican waters. Nine trips to Tecolutla estuary, Veracruz, Mexico, were taken between October 1995 and May 1998 to estimate the gonadal development and sexual dimorphism of G. dormitor. A total of 94 individuals ranging from 15–260 mm SL and 0.05–181 g were captured. Seventy-two specimens were adults (60 females, 12 males) and 22 were juveniles that did not show external sexual dimorphism. Both juvenile and adult stages of G. dormitor were captured year-round in seagrass beds and adjacent shallow, muddy or sandy areas. This study has shown that G. dormitor are resident and undergo sexual maturation in the Tecolutla estuary. Histological evidence suggests both males and females undergo gonadal recrudescence in the estuary and have an extended reproductive season from May through November. However, it is unclear if the species actually spawns in the estuary, since females in the final stages of oocyte maturation were not captured. Additional research on the reproductive biology and ecology of this under-studied species is necessary to determine its role in tropical estuaries in the southern Gulf of Mexico. Information learned from areas in the center of its distribution may aid in conserving the species at the periphery of its range in Florida, where it is considered threatened.