Molecular evidence suggesting interspecific hybridization in Zoanthus spp. (Anthozoa: Hexacorallia)

Interspecific hybridization has been proposed as a possible explanation for the incredible diversity seen in reef-dwelling corals, but until now little proof of such hybridization in other reef-dwelling anthozoans has been reported. Without further observation of hybridization, the question of such a phenomenon being widespread in Anthozoa remains. Here we have examined the mitochondrial cytochrome oxidase I gene (COI) and the nuclear internal transcribed spacer of ribosomal DNA (ITS-rDNA) from three species of the mass-spawning, encrusting anemone genus Zoanthus (Z. sansibaricus, Z. kuroshio, Z. gigantus) to investigate possible hybridization. The three species coexist at two of three sampling locations in southern Japan. Zoanthus spp. ITS-rDNA region spacers (ITS-1 and ITS-2) were shown to have very high rates of divergence. At locations where all three species co-existed, several of our sampled Z. sansibaricus individuals (with identical "sansi" COI sequences) possessed two very divergent (i.e., species-level difference) ITS-rDNA alleles, the expected "sansi" allele and the divergent "B" allele. Additionally, two Z. sansibaricus individuals possessed only "B" alleles despite having "sansi" COI sequences. These results indicate that Z. sansibaricus has possibly experienced interspecific hybridization at least once with a Zoanthus partner possessing the "B" allele, and that these resulting hybrids may also sexually reproduce, demonstrating potential hybridization occurring in the order Zoantharia (Hexacorallia).     

Some aspects of the reproductive biology of perch Perca fluviatilis L. A histological description of the reproductive cycle

Histological changes in the perch ovary during development are described and related to changes in gonad weight and to a macroscopic scale of maturity stages after Kesteven (1960). A single organ formed by the fusion of two primordial ovaries, a central internal oviduct, and an extremely thick chorion surrounding oocytes are characteristic features of the perch ovary. Resting oocytes can be differentiated from developing oocytes which are larger and possess a granulosa layer which permits formation of the chorion and yolk acquisition. In the maturing ovary, oocyte diameter increases rapidly and the chorion, which possesses four layers, the tunica propria, two middle zones forming a fine network, and the zona radiata, also expands. The spent ovary is disorganized with follicles and tunica wall contracted, and a number of residual oocytes may be apparent. There was no evidence of pre-ovulatory degeneration although autolysis of a small number of residual oocytes was observed. The gonadosomatic index was highest for males in September and at a maximum in females immediately prior to spawning. After spawning the index fell rapidly with lowest values recorded in June and July. Variations in the gonadosomatic index are related to developmental stages in females.     

Reconsidering Zoanthus spp. diversity: molecular evidence of conspecifity within four previously presumed species

We have conducted the first phylogenetic study to our knowledge of Zoanthus in the northern hemisphere by sequencing and analysing the mitochondrial cytochrome oxidase subunit 1 (COI) gene. Various unidentified Zoanthus specimens and samples of what have been assumed to be four discrete species (Z. pacificus, Z. sansibaricus, Z. gnophodes, Z. erythrochloros) were collected from four field sites in Kagoshima Prefecture, Japan. Based on our obtained COI gene sequences, all but one of our collected Zoanthus samples appear to be conspecific, with nearly 100.00% base pair matching. Genetic results are further backed up by collected polyp diameter, tentacle count, and mesentary count data. These results indicate a need to reconsider and re-analyze current Zoanthus classification and identification. Possible reasons for the large morphological variation in the same genotype in Zoanthus are also discussed.     

Cycle of gonadal development in Eunicella singularis (Cnidaria: Octocorallia): trends in sexual reproduction in gorgonians

Abstract. Eunicella singularis is a gorgonian species whose members are abundant in hard-bottom sublittoral communities of the Mediterranean Sea. The reproductive biology in this species has been examined to better understand the ability in this species to recover from recent mass mortality events. Eunicella singularis is a stable, gonochoric, iteroparous species that reproduces annually and exhibits a seasonal pattern of gametogenesis characterized by a single annual maturation of the gametes. The sex ratio did not significantly differ from 1:1. Oogenesis lasted 13–17 months, beginning between February and June, and ending with the release of 0.7 planula larvae per polyp between late May and July of the following year. The diameter of mature oocytes ranged 450–860 μm. Spermatogenesis was much shorter than oogenesis and occurred over 5–6 months. Gonadal production of both sexes increased in spring and culminated with the spawning of male colonies in late May–June. Fertilization of oocytes and development of the planula larvae occurred within the polyps of female colonies. Planula release was observed in June and July. The patterns emerging from this and previous studies on sexual reproduction of Mediterranean gorgonians suggest that investment in gonad development appears to be related to resource availability.     

Relationship between Marteilioides chungmuensis infection and reproduction in the Pacific oyster, Crassostrea gigas

Marteilioides chungmuensis, a protozoan paramyxean parasite, infects the oocytes of the Pacific oyster, Crassostrea gigas. The effects of infection on the reproductive cycle of C. gigas were investigated over two consecutive years at Okayama Prefecture, Japan. In male oysters, gonadal development began during February/March, maturity was achieved in June and spawning activity extended from July to September. In November and December, male oysters were not seen, probably because their gonads regressed to connective tissue and they transformed into undifferentiated oysters. By contrast, female oysters, in which parasite spore formation occurred, were still carrying oocytes until the following March and the spawning process of female oysters took 5 months longer than that of males in epizootic areas. The prevalence of M. chungmuensis infection increased from July to September, when most female oysters had their spawning period, and declined from October to the following April when oysters were at the spent stage. The prevalence of infection increased again in May of the following year and high prevalence was observed in the following July. When prevalence was compared between oysters of different age classes, higher prevalence was detected in older than in younger oysters. Histological examination showed that infected oysters produced oocytes continuously and spawned repeatedly from October to March, during which period healthy oysters were reproductively inactive. Parasites can infect the oocytes of infected oysters throughout the longer spawning period. These observations suggest that M. chungmuensis extends the reproductive period of infected oysters for its own reproductive benefit.     

Ovary of the golden crab,Chaceon fenneri: I. Post-spawning and oosorption

Oosorption has been considered an important strategy in many invertebrate species which occurs in response to behavioral, ecological, or physiological factors. In crustaceans, the early light microscopic studies of the ovary attributed a role in oosorption to follicle cells, hemocytes, or phagocytes. In this study, ovaries were collected from female golden crabs following spawning and processed for examination by electron microscopy. Following spawning, several unspawned oocytes which had become dissociated from their follicle cells were found in the ovaries. They appeared to be lodged within the lumen. Such oocytes were observed undergoing various stages of autolysis. At no time were hemocytes or recognizable phagocytes found in the lumen of the ovaries or in contact with the degenerating oocytes. Follicle cells which had surrounded the oocytes prior to the time of spawning exhibited disrupted membranes. Resorption of unspawned eggs appears to occur by autolysis of the individual oocytes. Several of the females who had recently spawned had numerous sperm in their ovaries. Such sperm may have been pressed into the lumen at the time of spawning or during the fixation process.     

Gross and histological observations of ovarian development and related condition changes in American plaice

The largest increase in gonadosomatic index of American plaice Hippoglossoides platessoides occurred between January and February. Hepatosomatic index was lowest in the spawning season, suggesting cessation of feeding activity during spawning, but rose immediately in July when condition factor recovered from its low spawning level. Increases in white muscle water content during the spawning season suggests protein depletion. Conservation of some white muscle fibres is suspected, but no regular pattern in area conserved was found. Gonad development was advanced in December and in April some gonads were showing evidence of spawning. Ovaries from spawning females showed hydration patterns and histological detail consistent with batch or serial spawning strategy. Evidence of recent spawning activity, including the presence of postovulatory follicles, was found in ovaries that also contained oocytes undergoing exogenous vitellogenesis. Oocyte size frequency distributions show a gap in size between cortical alveoli and vitellogenic oocytes prior to spawning which does not exist during the spawning season. This may represent the ability of plaice to push oocytes through vitellogenesis from a previtellogenic condition during the spawning period. The increased white muscle moisture during June and July may reflect the use of muscle protein to bring oocytes through vitellogenesis for the current spawning season.     

Life history of a simultaneously hermaphroditic fish,Diplectrum formosum

Sand perch Diplectrum formosum were collected in the Atlantic Ocean waters off the south‐eastern U.S. for life history analyses between April 2001 and July 2004 and ranged in size from 63 to 236 mm standard length (L_S) and 0–8 years of age. Diplectrum formosum are simultaneous hermaphrodites that reach 50% sexual maturity at 12·2 months and 122·8 mm L_S for testicular tissue and 13·6 months and 129·3 mm L_S for ovarian tissue. The gonad contains ovarian and testicular tissue separated by a thin basement membrane, with no means of internal self‐fertilization. Spawning females were found between March and January with a peak of spawning activity in May and a realized spawning periodicity of 2 days, equivalent to a maximum of 168 spawning events per year. Fish with testicular tissue in spawning condition were obtained throughout the year in every month sampled with a maximum frequency between June and September. There were also trends indicating that testicular tissue was more likely to be in spawning condition in the presence of hydrated oocytes within the accessory structure. This may indicate the use of the accessory structure as a storage site for hydrated oocytes until a mate can be located.     

High levels of morphological variation despite close genetic relatedness between Zoanthus aff. vietnamensis and Zoanthus kuroshio (Anthozoa: Hexacorallia)

Recent investigations into the encrusting anemone genus Zoanthus using molecular and morphological techniques have begun to bring order to this taxonomically neglected group. Previous studies have confirmed the existence of three distinct species present in southern Japan: Z. sansibaricus, Z. kuroshio, and Z. gigantus. Results from such studies show species of Zoanthus to be highly morphologically plastic, often incorporating morphotypes with varying oral disk color and oral disk diameter. Literature lists the species Z. aff. vietnamensis as occurring in southern Japan and throughout the western Pacific Ocean, but due to the morphological plasticity of Zoanthus species, a re-examination of Z. aff. vietnamensis using molecular techniques was needed. Here, using mitochondrial 16S rDNA and the nuclear internal transcribed spacer of ribosomal DNA (ITS-rDNA) sequences, as well as morphological data, we have examined several nominal Z. aff. vietnamensis samples collected from Kagoshima Bay and Yakushima Island, Japan. Based on polyp length and diameter, oral disk diameter, mesentery and tentacle numbers, and colony form, Z. aff. vietnamensis is easily distinguishable from Z. sansibaricus, Z. kuroshio, and Z. gigantus. However, despite these clear morphological differences, our mitochondrial and nuclear sequence-based phylogenies indicate that Z. aff. vietnamensis and Z. kuroshio are very closely related (perhaps conspecific), highlighting the morphological plasticity of this genus and the difficulty of species identification based on morphological data alone.     

Comparative study of sexual cycles, oogenesis and spawning of two Soleidae, Solea lascaris (Risso, 1810) and Solea impar (Bennet, 1831), on the western coast of Brittany

Two sand sole species, Solea lascaris and Solea impar , are common on the western coast of Brittany, France. Their reproduction (oogenesis and spawning) has been studied by following the gonadosomatic index, histological changes in ovary development, and oocyte diameter distribution. Both species have a prolonged spawning season, from spring to late summer. Each mature female breeds twice during the spawning season: in May and July for 5. lascaris , and in early June and July for 5. impar. Throughout the spawning season, several oocyte batches undergo vitellogenesis and there is a continuous recruitment of immature or primary oocytes into vitellogenesis. The two species are thus serial synchronous spawners. This, together with oocyte atresia late in the season (especially noticeable in S. impar ) makes fecundity estimation difficult.     

金沙江中游圆口铜鱼早期资源现状

2010年6月至7月在金沙江中游攀枝花格里坪金沙滩(26°35°28.96″N,101°31°52.01″E)设置同定采样断面,开展了金沙江中游圆口铜鱼早期资源现状的调查.结果表明,金沙江中游有金安桥、朵美、皮拉海、灰拉古、观音岩5个圆口铜鱼产卵场,产卵总量为3078.2万粒.圆口铜鱼的产卵行为和产卵量受江水的温度、流量、涨落水持续时间等多个因素的影响.调查期间圆口铜鱼的产卵初始时间为6月7日,盛期在6月下旬至7月上旬.近几年来,圆口铜鱼的产卵规模呈现出逐年下降的趋势,产卵场的位置也有所改变.通过了解金沙江中游江段圆口铜鱼早期资源分布状况,为金沙江中游圆口铜鱼资源保护提供了基础资料.     

Seasonal effects of melatonin on ovary and plasma gonadotropin and vitellogenin levels in intact and pinealectomized catfish, Clarias batrachus (Linn)

Effects of daily administration of melatonin for 15 days were evaluated with respect to ovarian activities and plasma gonadotropin (GtH II) and vitellogenin (Vg) levels in intact (INT) and pinealectomized (Px) female catfish, C. batrachus, during preparatory (April), prespawning (May and June), spawning (July) and post-spawning (September) periods. Px (saline control groups) caused a stimulatory effect during preparatory (with respect to Vg synthesis and incorporation) and prespawning (with respect to Vg synthesis) periods whereas no effect was observed during spawning and post-spawning periods with respect to the reproductive parameters studied. During April, melatonin-treatment significantly decreased plasma GtH II levels and percentage of vitellogenic oocytes without any significant changes in plasma Vg levels and gonadosomatic index (GSI). During early prespawning period, in May, 50microg melatonin brought about a significant reduction in plasma GtH II levels in INT group, whereas 100microg caused a decrease in all parameters; on the other hand, in Px groups both dose levels proved to be inhibitory. In June (late prespawning period) melatonin-treatment could not bring about any change in GSI and plasma Vg levels compared to the control groups regardless of Px but plasma GtH II and mean number of yolky oocytes were significantly reduced in melatonin-treated INT group. During spawning period (July) melatonin inhibited the GSI, mean number of yolky oocytes and plasma GtH II levels without affecting plasma Vg levels. In September (post-spawning period), melatonin did inhibit both GSI and plasma GtH II levels. The results, thus, indicate that melatonin showed variable effects (inhibitory and/or no effect) to GSI, mean number of yolky oocytes and plasma Vg levels but a consistent inhibiton of plasma GtH II levels indicating that melatonin may control the reproduction by blocking the GtH II release from the pituitary via affecting the hypothalamo-hypophysial axis.     

Semi-lunar spawning cycle and mating tactics in the marine goby <Emphasis Type="Italic">Asterropteryx semipunctata</Emphasis>

The reproductive behaviors of the marine goby Asterropteryx semipunctata were studied at Sakurajima, Kagoshima, Japan. Spawning occurred from late June to early October with a peak at 3–4 days after the full and new moon. This semi-lunar cycle might be advantageous to reducing nest-egg mortality but may not to larvae dispersion. Large males maintained spawning nests, and females spawned a whole clutch at a nest but with multiple males during a season. Females were less likely to be choosy due probably to a predation risk and/or nesting male shortage. Smaller males adopted sneaking tactics, and some of them became nesting males.     

Morphology of ovarian changes during the reproductive cycle of the fish, Mystus tengara (Ham.).

A study has been made of the morphological and histological changes of the cat fish (Mystus tengara) ovary during its reproductive cycle in natural and confined waters. This fish is oviparous and breeds once a year during the rainy season (July throught September). Factors responsible for bringing about spawning in fishes are discussed and the onset of spawning in Mystus is attributed to monsoon rains. In the ovarian cycle 7 phases have been recognised, whic are based on the gross morphological changes in the ovary, the percentage and duration of different developmental stages of oocytes, the average diameter and the gonosmatic index. They are: 1) immature virgin (November-February); 2) preparatory virgin (March-April); 3) maturing virgin (April-May); 4) pre-spawning virgin (June); 5) spawning (July-August); 6) depletion (September), and 7) recoupment (October-November). Oocyte growth has been divided into 9 stages. The ova diameter and gonosomatic index are maximum in July and minimum in November and December.     

Reproductive cycles in oregon populations of the echlnoid, Strongylocentrotvs purpuratus (Stimpson). I. Annual gonad growth and ovarian gametogenic cycles

Four annual reproductive cycles were followed in the echinoid, Strongylocentrotus purpuratus (Stimpson), at three places on the central Oregon coast near 44°45′N lat., where intermittent upwelling depresses coastal sea temperatures from June through September. Monthly measurements were made of the gonad index of samples of 30 urchins and the relative frequency of five stages in oogenesis were determined from sectioned ovaries from these samples.Individuals in these populations are synchronous in their annual cycle of gonad growth, oogenesis, and spawning, the latter taking place between late December and March. The population usually undergoes one major, complete spawning within a period of 30 days. When large reserves of stored nutrients are present, ova continue to mature over a longer period and may be present in quantity from December into April. Gonad weight does not change significantly from March through June. From July through November the gonad undergoes its annual growth at a mean instantaneous relative growth rate of ≈ 1 % per day. Gonad growth is not significantly correlated with sea temperature. Variable temperatures resulting from upwelling do not result in erratic fluctuations in the reproductive cycle, probably because of the annual change in feeding rate, the seasonal shift in energy utilization, and the constancy of the amount of food assimilated during gonad growth. Gonad size and annual growth rates may differ significantly between years and locations, indicating that both are influenced by local environmental factors, probably food availability and degree of wave action.The frequency of oogonial clusters is least in mid-winter, increases after spawning, reaches an annual maximum in June and declines in the fall. Primary oocyte growth is very slow until October, when it increases abruptly, and some oocytes become ova as early as late October. When stored nutrients are low, many oocytes do not complete growth by January, and are not spawned until May. Prolongation of the spawning period delays the increase in frequency of oogonial clusters in the following new cycle. The timing of the annual increase in oogonial cluster frequency and of the onset of rapid oocyte growth did not otherwise vary between places and years. In these populations, entrainment or synchronization of the reproductive cycle to seasonal environmental events probably occurs at the beginning of one or all of these critical annual events: oogonial proliferation, annual gonad growth and rapid oocyte growth.     

Reproductive activity in the checkered snapper, Lutjanus decussatus, off Ishigaki Island, Okinawa

The checkered snapper, Lutjanus decussatus, is an important species for fisheries in the Okinawan region. This study estimated the reproduction of this lutjanid species in the waters around Ishigaki Island. The main spawning season was estimated to be between June and October, since oocytes at the maturation stage and/or postovulatory follicles were found during the study period. In the main spawning season, high gonadosomatic index values were found around the time of the last quarter moon for each month from June to September. It is suggested that L. decussatus is a lunar-synchronized spawner off Ishigaki Island.     

Analysis of the cycle of reproduction of Sardina pilchardus (Walbaum, 1792) off the Moroccan Atlantic coast

This work focuses on aspects of reproductive biology of Sardina pilchardus from the Atlantic coast of Morocco. The mean values of batch fecundity estimated for the species is 23150(+/-1301) oocytes for a mean size of 19.5(+/-0.49) cm, the mean relative fecundity being 346(+/-7.34) oocytes per gram of female without ovary. Batch fecundity increases with total length and body weight without ovary. Sizes at first sexual maturity (L50) are reached for males and females at 15.8(+/-0.29) cm and 15.8(+/-0.35) cm, respectively. The spawning period for the population extends between October and July and the spawning peak occurs from October to February. However, the small sardines (14.5-17 cm) in their first reproduction spawn between November and June, whereas larger fish (17.5-25 cm) spawn between October and July. The factor of condition (K) increased in summer during the sexual resting phase. It is weak in winter during the period of reproduction. Regarding, the sex ratio, there was no significant difference in the number of males and females.     

Oogenesis in Vimba vimba (L. 1758) from Drawieński National Park (NW Poland)

The objective of the studies was to analyse the process of oogenesis in vimba from a non-migratory population living in the waters of Drawieński National Park in north-west Poland. The character of spawning of this species is an obstacle in determining the right moment to catch spawners or developing artificial spawning biotechniques. Previtellogenesis of vimba begins about six months after hatching and lasts three years. The trophoplasmatic growth of oocytes (October-March/April) begins when carbohydrate vesicles appear near the nuclei oocytes of sexually mature females (aged 4+). Just before spawning, granulated, lipoprotein-like substances are cumulated. The resorption of pre-ovulation corpora lutea (non-ejected oocytes) and post-ovulation corpora lutea (ruptured theca folds and follicles) begins in the ovary of vimba in the middle of June. These were observed in histological cross sections for about two to three months. Describing the process of oogenesis can provide a foundation for developing practical applications in aquaculture aimed at preserving the biodiversity of the park's waters and this critically endangered species of the Polish ichthyofauna.     

Feeding migration of roach, Rutilus rutilus (L.), in Lake Arungen, Norway

In the period April–July 1980 we studied the feeding migration and food of roach in a small tributary of the eutrophic Lake Årungen, south-eastern Norway. Tagging experiments revealed a tendency in roach to utilize a specific tributary both for feeding and for spawning. The mean size of roach ascending the tributary in late June and July was significantly larger than the mean size of roach spawning 1–2 months earlier, probably due to higher water discharge in July than in May and June. The experiment indicates two separately motivated migrations involving homing. The roach fed more profitably in the tributary than in the lake, both in terms of food availability and predator avoidance.     

Reproductive biology ofAwaous guamensis, an amphidromous Hawaiian goby

Synopsis Spawning season, size at first reproduction, oocyte maturation, and fecundity ofAwaous guamensis, an amphidromous Hawaiian goby, were studied from June 1989 through May 1991 in the Wainiha River, Kau'ai, Hawai'i. Female fish larger than 73 mm standard length (SL) had mature gonads from August through December in 1989 and 1990. Gonadosomatic index (GSI) values for mature females ranged from 0.2 to 14.5 during the spawning season. Male fish larger than 64 mm SL had elevated GSI values from June 1989 through December 1989 and from August 1990 through December 1990. Mature sperm were found in two male fish collected in January and February. GSI values for mature males ranged from less than 0.01 to 4.0 in the spawning season. Size-frequency distributions of measurements of vitellogenic oocyte diameters and microscopic observations of oocytes indicated this species has group-synchronous oocyte development. Ovarian maturation stages examined over a 29-month period suggest that members of the stock spawned at different times within the spawning season, although mass spawning events have been documented for this species. Estimates of clutch sizes from nests measured in situ were comparable to estimates of potential fecundity from in vitro examination of ovaries, and indicated that female fish deposited an entire clutch during a spawning event. No evidence for multiple spawning by an individual fish in a single season was found. However, microscopic observations of brown bodies in some ovaries suggested that individual fish probably spawn more than once in a lifetime.