Juvenile bisexuality in the red sea bream,Pagrus major

The histology of the gonad of the red sea bream,Pagrus major, was examined in order to study the early gonadal development, sexual maturation and sex ratio in a natural population. A total of 1,117 fish between the ages of 4 months and 8 years were examined. Gonads of 4-month-old fish were either sexually undifferentiated with a central cavity, or ovarian in form. Gonads of 12- and 18-month-old fish were ovaries or bisexual gonads, while those of 2-year-old fish were ovaries, bisexual gonads or testes. Fish aged between 3 and 8 years had ovaries or testes, except for a few bisexual gonads found in 3- and 4-year-old fish. The chronological appearance of females, hermaphrodites and males in that order, and histological evidence, suggested that the testis originates from the ovary via a bisexual gonad in the juvenile stage. The sex ratio of females to males at the age of 2 years and over was about 1:1, suggesting that hermaphroditic red sea bream appear in about 50% of the juvenile population. The sexual pattern in this species, therefore, is concluded to be gonochorism with a bisexual juvenile stage.     

A histological description of intersexuality in the roach

This paper is an illustrative guide to intersex in the roach Rutilus rutilus , based on 150 intersex individuals. Most intersex roach had female germ cells, or oocytes, within a predominantly male gonad (testis), and/or malformed/intersex reproductive ducts. The number, pattern and developmental stage of oocytes within testicular tissue in intersex fish varied greatly. In most intersex fish, a few primary oocytes, or numerous primary and secondary oocytes, were scattered randomly throughout the testicular tissue (multifocal intersex). In other, more severely feminized individuals, large areas of ovarian tissue were separated clearly from testicular tissue (focal intersex). Almost all intersex individuals had a female-like reproductive duct (ovarian cavity). In mild cases of intersex (in which the majority of the germ cells were male) the ovarian cavity was present together with the male sperm duct/vas deferens, whilst in certain severe cases, the sperm duct was absent or vestigial.     

THE OCCURRENCE OF HISTOCHEMICAL ACTIVITY OF 3β-HYDROXYSTEROID DEHYDROGENASE IN THE DEVELOPING TESTES OF POECILIA RETICULATA

In the mature testes of the guppy, Poecilia reticulata , some groups of cells, distributed sparsely in the interspace between the peripheral germ cell layer and the hilar duct system, show evident histochemical response for Δ⁵-3β-hydroxysteroid dehydrogenase (3β-HSD). In the testis of newly delivered guppies, somatic cells are present in the testicular hilus as a compact mass without revealing any structural differentiation. In the testis of juvenile fish of the 8mm stage about 7 days after birth, interstitial cells resembling histologically those of adult testes become differentiated from the somatic cell mass and, though only in some specimens, coincidentally begin to display weak but obvious histochemical response for 3β-HSD. Thereafter the occurrence of enzyme activity becomes increasingly regular in the developing testes, and attains the adult pattern of distribution in testes of all specimens after the 11 13mm stage or 17 ∽ 20 days of age.
The appearance and enhancement of 3β-HSD activity in the testis is concurrent with the differentiation and development of the testicular duct system. Treatments of newly delivered fish with methyltestosterone (30 ∽ 50 μg/g diet) distinctly stimulate the development of the duct system, which suggests a possible role of androgen secretion occurring in the early phase of the testicular development in the control of testicular organogenesis in the guppy.     

The distribution of an invasive fish species is highly affected by the presence of native fish species: evidence based on species distribution modelling

Topmouth gudgeon (Pseudorasbora parva) is one of the most invasive aquatic fish species in Europe and causes adverse effects to ecosystem structure and functioning. Knowledge and understanding of the species’ interactions with the environment and with native fish are important to stop and prevent the further spread of the species. Creating species distribution models is a useful technique to determine which factors influence the occurrence and abundance of a species. We applied three different modelling techniques: general additive models, random forests and fuzzy habitat suitability modelling (FHSM) to assess the habitat suitability of topmouth gudgeon. The former two techniques indicated that the abundance of native fish (i.e. biotic variables) was more important than environmental variables when determining the abundance of topmouth gudgeon in Flanders (Belgium). Bitterling (Rhodeus amarus), stone loach (Barbatula barbatula), three-spined stickleback (Gasterosteus aculeatus) and predator abundance were selected as the most important biotic variables and implemented in the FHSM to investigate species interactions. Depending on the preferred food source and spawning behaviour, either coexistence or interspecific competition can occur with bitterling, stone loach and three-spined stickleback. In contrast, the presence of predators clearly had a top down effect on topmouth gudgeon abundance. These findings could be applied as a biological control measure and implemented in conservation strategies in order to reduce the abundance of earlier established populations of topmouth gudgeon.     

The use of spontaneous behavior,swimming performances and metabolic rate to evaluate toxicity of PFOS on topmouth gudgeon Pseudorasbora parva

Perfluorooctane sulfonate (PFOS) is a ubiquitous environmental contaminant that has been found to pose various risks to fish health and the safety of aquatic ecosystem. Swimming performance is an integrated index of fitness in fish. However, little research has sought on the effects of PFOS on swimming performances of fish. Experiments were carried out to clarify the impacts of acute exposure to PFOS on behavior, swimming ability and metabolic rate in topmouth gudgeon (Pseudorasbora parva), to understand the underlying ecotoxicological effects of waterborne PFOS exposure on fish physiology and behavior. Fish were exposed to PFOS (0, 0.5, 2, 8 or 32 mg/L) for 96 h. Afterwards, the routine metabolic rate (RMR), spontaneous swimming behavior (SSB), fast-start swimming performance (FSP) and critical swimming speed (U_crit) of the topmouth gudgeon were examined. The results show reduced behavioral performance and increased physiological stress with increasing PFOS concentration. Both RMR, SSB and U_crit were significantly affected by PFOS exposure (p < 0.05). The lowest observed effect concentration (LOEC) is 2 mg/L for SSB. PFOS treatment resulted in increased RMR (p = 0.001) and decreased U_crit (p = 0.005), whereas FSP was not influenced by PFOS (p > 0.05). The results indicate that the anaerobic swimming capacity was conserved, but the metabolic level, SSB and aerobic swimming performance in topmouth gudgeon were susceptible to PFOS contamination, and hence might be useful as considerable potential biomarkers of pollution.     

Feeding habits and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake,central China

The diet and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91–539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.     

Reproductive parameters of topmouth gudgeon (Pseudorasbora parva) from a heated Lake Licheńskie (Poland)

Temperature regime is known to have considerable influence on the life-histories of fish. Topmouth gudgeon is a very successful invader with high biological flexibility and phenotypic plasticity. The flexibility of topmouth gudgeon in a normal thermal regime has been well described, however there has been no information published about how it would cope with extreme conditions, e.g. permanently heated water. Several studies have demonstrated that phenotypic plasticity provides an important advantage to invasive species. To explain their invasion success, the theory of alternative ontogenies and invasive potential has been proposed. The aim of the present study was to examine if the reproductive parameters of a population living in permanently heated water differ from those living in habitats with a normal temperature regime, as well as to test a hypothesis derived from the theory of alternative ontogenies and invasive potential. Over a period of 8 years (2004–2011), a high variation in the reproductive parameters of topmouth gudgeon from Lake Licheńskie was found. With a small exception, all the observed results met the expectations predicted by the hypothesis tested. This indicates that topmouth gudgeon retains high phenotypic plasticity in life-history traits even in a habitat with extreme conditions, which is important for the species’ invasion success.     

Escapees of potentially invasive fishes from an ornamental aquaculture facility: the case of topmouth gudgeon Pseudorasbora parva

Accidental escapees from aquacultural facilities are an ongoing problem facing scientists, conservationists, policy makers and naturalists throughout the world. The topmouth gudgeon Pseudorasbora parva , a small cyprinid native to Southeast Asia, was introduced to Romanian waters in 1960 via the aquaculture trade and has since spread throughout Europe. It first appeared in England in an ornamental fish farm near Romsey in Hampshire. The aim of the present study was to quantify the dispersal of this potentially highly invasive species from an ornamental fish farm into the wild. In order to measure the dispersal of escapees, intensive electrofishing surveys were carried out between June and September 2003 in the catchment downstream of the fish farm. The distribution of topmouth gudgeon in the catchment was found to be limited and patchy. The presence of small individuals suggests that the species has successfully established itself in the wild, but this remains to be confirmed. The results were examined in light of invasion theory principles of biological resistance and ecological fitness.     

Reproductive demographics,intersex, and altered hormone levels in shortnose sturgeon,Acipenser brevirostrum,from Delaware River,USA

Non‐lethal sampling techniques were used to document the reproductive structure of the shortnose sturgeon (Acipenser brevirostrum) population at a fish aggregation site (near Bordentown, New Jersey) in the Delaware River. A total of 68 fish were captured using gill nets (100 × 1.8 m, 12.7 or 15.2 cm mesh) and examined laparoscopically in May–June, and 61 additional fish captured and examined in November during 2006–2011. Six stages of reproductive development were identified in females and five stages were identified in males, encompassing differentiation through maturity in both sexes. Fish captured in the spring were predominantly immature with a higher proportion of females (1 : 1.2 M : F sex ratio), while mature males predominated in the autumn (5.7 : 1 M : F), indicating that the Bordentown area serves as an overwintering/pre‐spawn aggregation site. Three distinct forms of intersex were noted in gonads of 11.6% of fish examined: ovo‐testis, consisting of scattered spermatic cysts in predominantly immature ovary (3.9%); testis‐ova, consisting of ovarian lamellae projecting from a predominantly immature testes (4.7%); and zonal distribution, consisting of multiple, nearly‐homogenous pockets of either testicular or ovarian tissues along the gonad (3%). The hormone profile in fish with ovo‐testis was similar to that of immature males, while the hormone profile in fish with testis‐ova was similar to that of immature females. The relatively high prevalence of intersex raises concerns regarding potential reproductive effects and long‐term impacts on shortnose sturgeon in the Delaware River.     

Gonadal morphology of threadfin breams,Nemipterus bathybius andN. virgatus: Evidence of rudimentary hermaphroditism

Gonads of young and adultNemipterus bathybius andN. virgatus were examined histologically. In youngN. bathybius males, the testis is composed of a dorsal and a ventral zone separated by thin connective tissue. A duct runs through the center of the dorsal zone, and has an opening on the ventromedian surface of the body, separate from the male genital pore. Along with the start of spermatogenesis in the ventral zone, germ cells distributed in the dorsal zone also begin spermatogenesis and eventually develop into spermatozoa. Consequently, in mature testes the sperm sinuses are formed to enclose the dorsal duct, leaving a small number of germ cells, including oviform cells, retained in the lamellar projections of the duct. Testes ofNvirgatus also have essentially the same histological characteristics. No trace of testicular tissue is present in the ovaries, except in four cases of intersexual gonads found in both nemipterid species. It is concluded that the dorsal duct and its lamellar projections are remnants of the ovarian cavityoviduct system and ovigerous lamellae of the ovarian portion of the gonad, and that these two nemipterid species are rudimentary hermaphrodites in which males have bisexual gonads of the delimited type in their juvenile stages.     

Genetic variation of the mtDNA <Emphasis Type="Italic">cyt b</Emphasis> locus in topmouth gudgeon introduced into water bodies in the northern part of the Black Sea region

The up-to-date phylogeographical distribution of the topmouth gudgeon Pseudorasbora parva Temminck et Schlegel 1846 in water bodies of the Northern Black Sea region is considered. Genetic variation of mtDNA cyt b gene is analyzed. It is established that topmouth gudgeon penetrated and spread in the basins of the Dnieper and Don rivers and in water bodies of Crimea from the secondary center of its dispersion— water bodies of Central Europe. It is demonstrated that haplotypes of topmouth gudgeon in the Danube delta are the most homologous to the haplotypes in the native range of the species in China. A considerable decrease in the level of genetic variation in the populations in the Black Sea region is reported.     

Top-down control of a meiobenthic community by two juvenile freshwater fish species

Top-down control of prey assemblages by fish predation has been clearly demonstrated for zooplankton and macroinvertebrates. However, in the benthic communities of freshwater ecosystems, the impact of fish predation on meiofaunal assemblages is nearly unknown. In this study, the predation effects of juvenile carp (Cyprinus carpio) and gudgeon (Gobio gobio) on meiofaunal abundance, biomass, community structure, and the diversity of nematodes were examined using microcosms that were sampled repeatedly over 64 days. Significant differences in abundance and biomass were found between the two fish treatments (carp and gudgeon) and their respective controls for nematodes, oligochaetes, and crustaceans (copepods, harpacticoids, ostracods, and cladocerans), but not for rotifers. These changes were consistent with top-down control of the freshwater meiofaunal assemblages in the microcosms over time. By contrast, small-bodied meiofauna was more abundant, suggesting indirect facilitation. Neither the species richness nor the diversity of the nematode community was affected by fish predation. The results indicate that predation by juvenile freshwater fish depresses the overall abundance and biomass of meiofaunal assemblages, except for rotifers, and alters the size structure of the meiofaunal community. Therefore, the meiofaunal assemblages of freshwater ecosystems may be influenced by bottom-feeding juvenile fish, e.g., carp and gudgeon, through top-down control of meiofaunal populations.     

Estrogen synthesis in relation to gonadal development of Japanese scallop, Patinopecten yessoensis: gonadal profile and immunolocalization of P450 aromatase and estrogen

Aromatase activities and estrogen contents in the gonad of Japanese scallop, Patinopecten yessoensis, were determined during gonadal development and estrogenic cells in the testis were identified immunohistochemically. Ovaries and testes developed rapidly during January and February to reach the mature stage in March and the spawning stage in April. Increases in aromatase activities of the ovary and testis preceded the onset of the ovarian and testicular development. Aromatase activities reached the highest level at the growing stage in February and the mature stage in March, and showed a striking decrease at the spawning stage in April. Contents of ovarian and testicular estradiol-17beta changed similarly to the profile of aromatase activities in the ovary and testis, although estrone showed no change. Immunoreactivities against P450 aromatase and estradiol-17beta were detected in the cells along the inside of the acinar wall of the testis, whereas in the previous reports, the cells are distributed along the outside of the acinar wall in the ovary. This study thus suggests that estrogen is synthesized in the estrogenic cells of the ovary and testis through aromatization by P450 aromatase and that testicular estrogen may play a physiological role in spermatogenesis.     

Contribution of the scrotum,testes, and testicular artery to scrotal/testicular thermoregulation in bulls at two ambient temperatures

The objective of this study was to determine the contribution of the scrotum, testes, and the testicular artery to scrotal/testicular thermoregulation in bulls at two ambient temperatures. Crossbred beef bulls, 1.5 years of age, were placed in controlled environment chambers at ambient temperatures of 15°C (n = 5) or 25°C (n = 6). The distal lateral aspects and entire ventral part of the scrotum was incised under caudal epidural anaesthesia (xylazine, 0.07 mg kg⁻¹). Both testes were withdrawn from the scrotum and then replaced and maintained by clamping the scrotal incisions with towel clamps. One testis was randomly chosen to be the exposed testis and was withdrawn prior to temperature measurements. Surface and internal temperatures were measured with infrared thermography and needle thermocouples, respectively. Temperature gradients (°C; difference in temperature from top to bottom at 15 and at 25°C) were: scrotal surface (with testis), 1.5 and 1.3; scrotal surface (without testis), 2.1 and 1.6; surface of exposed testis, −0.6 and 0.0; sub-tunic of exposed testis, −2.2 and −0.6; intratesticular (covered testis), 0.0 and 0.4; and intratesticular (exposed testis), −1.3 and 0.4. The scrotum markedly affects testicular temperature but the testes have limited influence on scrotal surface temperature. The bovine scrotum and testes have opposing temperature gradients that complement one another, resulting in a relatively uniform intratesticular temperature. These temperature gradients are attributed in part to the testicular artery, which goes from the top of the testis to the bottom, divides into several branches and ramifies dorsally and laterally before entering the testicular parenchyma. Intra-arterial temperatures (measured with needle thermocouples) were lower (P < 0.05) where the artery entered the testis than at both the bottom and top of the testis for both the covered (31.7, 33.4 and 34.3°C) and exposed testis (29.6, 32.0 and 32.5°C) at an ambient temperature of 15°C. Temperature differences were similar, but less pronounced, at 25°C (covered testis, 34.8, 36.3 and 36.5°C; exposed testis, 32.4, 33.5, 33.9°C). Results supported the hypothesis that blood within the testicular artery has a similar temperature at the top of the testis (just ventral to the testicular vascular cone) compared with the bottom, but subsequently cools before entering the testicular parenchyma.     

Ontogenetic testicular development and spermatogenesis in rays: the Cownose Ray,Rhinoptera bonasus,as a model

An understanding of testicular anatomy, development, and seasonality has implications for studies of morphology, behavior, physiology, and bioenergetics of males. Ontogenetic testicular development and spermatogenesis is essentially unknown for chondrichthyans. We examined embryo, juvenile, and adult male Cownose Rays (Rhinoptera bonasus) during development and throughout the annual reproductive cycle. Spermatogonia and Sertoli cells originated from germ cells and somatic cells, respectively, in the embryonic testicular germinal epithelium. In embryos and small juveniles, discrete regions of spermatocyst production appeared within a series of papillae that projected from the dorsal surface of each testis. Because these papillary germinal zones appeared to proliferate through ontogeny, we hypothesize that (1) the germinal zones of juvenile and adult testes are derived from embryonic testicular papillae that form from the germinal epithelium and (2) the papillae become the dorso-central portion of the distinct testicular lobes that form at maturation due to increased spermatocyst production. Our observations indicate that testicular development and the process of spermatogenesis began during embryonic development and increased in scale through ontogeny until maturation, when distinct testicular lobes formed and began enlarging or shrinking based on the annual reproductive cycle. Gonadosomatic indices peaked corresponding to seasonal increased sperm production between January and April, just prior to the April–June mating period. In all life stages, spermatocysts had efferent ducts associated with them from their formation through all stages of development. Year-round presence in the Charlotte Harbor estuarine system, Florida made R. bonasus a good model for beginning to understand ontogenetic gonad development and spermatogenesis in chondrichthyans, especially viviparous rays.     

Gonadal development and diandric protogyny in two populations of Dascyllus reticulatus from Madang, Papua New Guinea

Two Dascyllus reticulatus populations from Madang, Papua New Guinea exhibited diandric protogyny. In both populations, gonads began as undifferentiated, and then developed oocytes in the primary growth stage and an ovarian lumen. From this ovarian state or from more developed ovaries containing oocytes beyond the primary‐growth stage, some gonads developed into testes. The first sign of testicular development was degeneration of oocytes, degeneration of oocytes in the primary growth stage in ovarian gonads and degeneration of oocytes of all growth stages present including the primary growth stage in ovaries, which was then followed by development of spermatogenic tissue. In both populations, most of the fish that had gonads with degenerating oocytes were smaller than the smallest mature females, indicating that development towards testes was mostly initiated in immature gonads containing only pre‐vitellogenic oocytes. On some occasions, however, females as large as other mature females also had gonads with degenerating oocytes, suggesting that development towards testes may have occurred in mature ovaries as well. This latter notion is further strengthened by the discovery of a fish having a gonad that contained both degenerating vitellogenic oocytes and developing spermatogenic tissue. Taken together, these results suggest that D. reticulatus can exhibit diandric protogyny, because testes in D. reticulatus developed from juvenile gonads as well as from mature ovaries.     

Piscivorous fishes diet dominated by the Asian cyprinid invader,topmouth gudgeon (<Emphasis Type="Italic">Pseudorasbora parva</Emphasis>)

Predation on the non-native cyprinid, Pseudorasbora parva, was reported during an annual study in a small connecting canal about 40 km south of Brno, Czech Republic. Two cyprinid fish species (Pseudorasbora parva, Rutilus rutilus) were identified in the diet of 23 piscivores belonging to three native fishes (Perca fluviatilis, Sander lucioperca, Esox lucius). The relative abundance of prey fishes changed seasonally and was dominated by the topmouth gudgeon in spring. Thereafter roach incidence continuously increased. In contrast, topmouth gudgeon was found to be a more sized-available prey and was the most dominant prey species in the diet of all piscivorous fishes during the whole season. Strong piscivory towards this alien might be beneficial for its eradication or control to support ecological integrity in natural and modified seminatural habitats.     

Annual changes in testicular development and occurrence of parasperm in the male reproductive organs of fourspine sculpin, Cottus kazika

Annual changes in testicular development and occurrence of parasperm were investigated using 2-year-old male fourspine sculpins Cottus kazika, based on the histological observation of testes. The male reproductive organ of fourspine sculpins comprised a pair of testes and a sperm duct that functioned as a sperm-storage organ. Male maturity was divided into the following periods: spermatogonial proliferation period (September), early spermatogenic period (October), mid-spermatogenic period (November), late spermatogenic period (December and January), functional maturation period (February and March), and recovery period (April to August). Spermatogenesis rapidly progressed from October to January and continued until the functional maturation period. Parasperm formation, which is known in some cottidae species, was observed in fourspine sculpins. Testicular regression of cultured fourspine sculpins progressed slowly during the recovery period when residual parasperm and empty spaces occupied the testis. The parasperm were immotile and oval and slightly concave on one side; additionally, they stained strongly with hematoxylin and PAS. Seminal lobules of the testis were filled with parasperm during the spawning period; in contrast, the sperm duct was filled with eusperm. These findings were observed in both cultured and wild fish. In this study, the functions of parasperm with regard to reproduction in fourspine sculpins are discussed.     

Can sunbleak Leucaspius delineatus or topmouth gudgeon Pseudorasbora parva disperse through saline waters?

In order to determine the potential for the invasive fishes sunbleak Leucaspius delineatus and topmouth gudgeon Pseudorasbora parva to disperse through saline waters their behaviour and physiology were investigated during exposure to salinities of 10·0 and 12·5. Increased salinity caused an increase in whole body cortisol in both species, but sunbleak and topmouth gudgeon showed very different metabolic and behavioural responses to the salinity stress. Sunbleak displayed increased swimming activity in brackish water, which may be important for dispersal through saline waters in the wild, although there were increased metabolic costs associated with this behaviour. Conversely, topmouth gudgeon showed a reduction in both swimming activity and metabolic rate in brackish waters. A pronounced depression in food intake (70–80%) was shown by both species during the salinity exposures. Both sunbleak and topmouth gudgeon, however, showed a full recovery of food intake within 24 h following return to fresh water. Despite the fact that exposure to saline waters is stressful, and affects both physiology and behaviour, rapid recovery of appetite after return to fresh water suggests that short-term use of brackish waters is a feasible dispersal route for sunbleak and topmouth gudgeon in the wild.