Structural characteristics of gonadal development and hermaphroditic phenomenon in freshwater pearl mussel,Sinohyriopisis schlegelii (Hyriopisis schlegelii)

The period of gonads development was first studied from one to five years in the freshwater pearl mussel Hyriopisis schlegelii. It lasted for 36 months and was divided into three main stages: initiation of gonad formation, a stable growth phase, and a reproductive cell development phase. Each reproductive cycle consisted of five stages: proliferative stage (from late January to late February), growth stage (from late February to late March), maturation stage, spawning stage (from early April to late October) and recovery stage (from early November to late January). Interestingly, a hermaphroditic phenomenon was observed in this mussel for the first time, which appears during the development stage from 26 to 32 months. Male and female follicular tissues coexisted in hermaphrodite individuals with the male follicular tissue accounting for more than 90% of the whole gonad tissue. No hermaphroditic phenomenon was observed in matured gonad. We thus speculate that self-fertilization does not exist in H. schlegelii.     

Histology of the reproductive tissue of the clam Ruditapes decussatus from the gulf of Gabès (Tunisia)

Summary

The gametogenic cycle of the clam Ruditapes decussatus was investigated during one year. Samples were collected each month in two different sites located at the gulf of Gabès area. Gametogenic activity was characterized on the basis of histological analysis of the gonads. A classification and a scoring system were then proposed. According to our study, Ruditapes decussatus gametogenesis can be divided in four major steps: (1) a sexual rest (December- February), (2) starting of gametogenesis (February-March), (3) development (March-May), (4) ripe (from April onwards). This study revealed that the gonad of the clam Ruditapes decussatus was surrounded by muscular tissue which could represent the principal storage tissue. Two kinds of hermaphroditism appeared since maturity of gonads: simultaneous one showing gonadal tubules of both males and females in regionally distinct and separate zones and a “superposed” one showing a gonad consisting essentially of mature male gametes and few residual oocytes.     

Stranding events provide indirect insights into the seasonality and persistence of jellyfish medusae (Cnidaria: Scyphozoa)

It is becoming increasingly evident that jellyfish (Cnidaria: Scyphozoa) play an important role within marine ecosystems, yet our knowledge of their seasonality and reproductive strategies is far from complete. Here, we explore a number of life history hypotheses for three common, yet poorly understood scyphozoan jellyfish (Rhizostoma octopus; Chrysaora hysoscella; Cyanea capillata) found throughout the Irish and Celtic Seas. Specifically, we tested whether (1) the bell diameter/wet weight of stranded medusae increased over time in a manner that suggested a single synchronised reproductive cohort; or (2) whether the range of sizes/weights remained broad throughout the stranding period suggesting the protracted release of ephyrae over many months. Stranding data were collected at five sites between 2003 and 2006 (n = 431 surveys; n = 2401 jellyfish). The relationship between bell diameter and wet weight was determined for each species (using fresh specimens collected at sea) so that estimates of wet weight could also be made for stranded individuals. For each species, the broad size and weight ranges of stranded jellyfish implied that the release of ephyrae may be protracted (albeit to different extents) in each species, with individuals of all sizes present in the water column during the summer months. For R. octopus, there was a general increase in both mean bell diameter and wet weight from January through to June which was driven by an increase in the variance and overall range of both variables during the summer. Lastly, we provide further evidence that rhizostome jellyfish may over-wintering as pelagic medusa which we hypothesise may enable them to capitalise on prey available earlier in the year. Handling editor: K. Martens     

Growth and age determination of the tropical Australian cubozoan Chiropsalmus sp.

Chiropsalmus sp. medusae collected in this study ranged from 3 to 71 mm diagonal bell width and displayed growth best described by the following equation size (mm) = 74.9 × exp (−exp(0.041 (time since metamorphosis (day) −35.6674))). Growth rates of up to 7 mm week⁻¹ increase in diagonal bell width are theoretically possible, with animals able to reach sexual maturity in approximately 70 days. Correlation of the number of rings on the statoliths with the predicted age of the individual from the field produced a relationship that indicates the growth rings are laid down daily and as such could be used to infer age of the medusae. Over the 1998–1999 season, there were four influxes of juvenile cohorts, each occurring approximately 14 days after a major rainfall event.     

Reproductive cycle and reproductive output of the sea urchin Loxechinus albus (Echinodermata: Echinoidea) from Beagle Channel, Tierra del Fuego, Argentina

Reproductive cycle, frequency and duration of spawning, energetic content of gonads, and reproductive output of the common green sea urchin Loxechinus albus were analyzed in the Beagle Channel (Tierra del Fuego) between May 2004 and May 2005. Gonad indices (GI, percentages of gonad mass in total body mass) were significantly higher in March, April, July, and August than in November and May, thus showing a negative correlation with the photoperiod. Highest GI values of mature individuals were observed in August, and spawning occurred from September to December. In females, the mass-specific energy content of gonads (ECG) was highest in spawned gonads and lowest in mature ones, while in males ECG values were higher in immature stage and lower in premature and mature stages. High ECG values can be explained by the abundance of nutritive phagocytes. Both ECG and total gonad energy content (TECG) were higher in females than in males. Mean reproductive output was 7.28% for females and 6.15% for males (expressed as the difference between mean GI of mature and spawned gonads) and 25.02 kJ for females and 19.26 kJ for males (expressed as the difference between mean TECG of mature and spawned gonads).     

Seasonal changes in energy allocation to somatic and reproductive body components of the common cold temperature sea urchin <Emphasis Type="Italic">Loxechinus albus</Emphasis> in a Sub-Antarctic environment

Monthly variations in the somatic indexes and energetic content of organs were investigated in Loxechinus albus from the Beagle Channel. Samples were collected monthly from May 2004 to May 2005. Lantern and test indexes did not vary significantly. A major peak of gonad index (GI) was observed in winter (sexual maturation period), with a strong declination in November suggesting a spawning period in spring. In coincidence a shortening of feeding activities was expressed by the lower values of gut index (Gut I), suggesting that the gut is a storage organ. The values of gonad energetic content (GEC) and total gonad energetic content (TGEC) showed minimum values in winter (ripe stage) and the maximum in spring (spawned stage). The TGEC reached higher monthly average values (50–200 kJ) than total gut energetic content (TGuEC) (20–40 kJ). These differences indicate that the gonads constitute the most important store organs in L. albus. Moreover, organic stores are built up in the gonads after spawning, and then utilized during gamete production.     

Chemische Zusammensetzung und Biomasseparameter der OhrenqualleAurelia aurita

During summer 1982 and 1983, measurements on the chemical composition and biomass parameters ofAurelia aurita from Kiel Fjord, Western Baltic, were made. The relationships between size vs. wet weight and wet weight vs. carbon content were determined. Dry weight accounted for less than 2% of wet weight in both years. Carbon, nitrogen and phosphorus content of whole medusae were 51–52, 14 and 1.4 mg/g dry weight (dw) respectively. The C:N ratio (by weight) was about 3.7 and the C:N:P-ratio (by atoms) was determined to be 94:22:1. Proteins and carbohydrates made up 59 and 29 mg/g dw. Lipids were estimated to be 19 mg/g dw. Using these data, it was possible to calculate the caloric content of the medusae to be about 0.55 cal/mg dw. In summer 1982, the organic content of different tissues (gonad, oral arm, umbrella) in unfertilized and fertilized females was studied. In unfertilized females, the gonads exhibited the highest values, the umbrella had the lowest values and the values of oral arm tissue were intermediate. However, in fertilized females the oral arm tissue was enriched, whereas the gonads were impoverished; both types of tissues exhibited very similar values. This pattern can be explained by the transfer of fertilized eggs from the gonads into the brood pouches of the oral arms.     

Life history patterns of the common carp,Cyprinus carpio,in the estuary of the Guadalquivir river in south-west Spain

We examined 1567 carp caught in rice field drainage canals in the estuary of the Guadalquivir river (37° N, 6° 25 W). The stock was comprised of a small number of age groups, among which 0+ and 1+ were dominant. Growth was divided in four periods: rapid (June–July); slow (August–November), no growth (December–March), and resumed growth in April when an annulus was formed. A classification based on 12 wild carp populations revealed that growth depends on latitude, and that growth of the studied stock was mediocre, probably due to high salinity. A decrease in somatic condition coincided with an increase in gonadosomatic index (GSI). Specimens of the same stock, age and/or length showed considerable difference in development of the gonads. Gonadal activity began in September and by late Autumn some gonads had reached up to 20% of body weight. The situation remained static during Winter till April, when most reproduction occurred. Later, GSI values decreased to reach a minimum in September.Maximum average GSI values in females were twice those in males. Both sexes achieved maturity during the third growing season (2+ age-group) at a minimum fork length (F.L.) of 110 mm. Fecundity, before reproduction, was expressed by Fec = 241.701 F.L. (mm) – 26776.2. The sex ratio did not differ significantly from 1 : 1.     

REPRODUCTIVE PERIODICITY OF THE SEA URCHIN,TRIPNEUSTES GRATILLA (L.) IN TAIWAN COMPARED WITH OTHER REGIONS

An annual reproductive periodicity of Tripneustes gratilla in northern Taiwan is revealed by both the gonad development stages and the gonad index. The gonads of T. gratilla recovered from spawning in February—March, propagated gametocytes in April—June, came to prematurity in July—August, and matured in September—November. Spawning occurred in October—December. The breeding pattern of T. gratilla over a broad geographical area appears to be related to seasonal changes of sea temperatures.     

Long-Term Changes in the Gonad Condition of the Sea Urchin Strongylocentrotus intermediusfrom Alekseev Bight (Amurskii Bay) under Polluted Conditions

The gonad condition of the sea urchin Strongylocentrotus intermediuscollected in August 1997 at two stations in Peter the Great Bay was examined. One of the stations was located in a polluted area (Alekseev Bight, Popov Island) and the other, in a relatively clean area (the Verkhovskii Islands). The results were compared with analogous data for 1984, 1985, and 1989. In 1997, the gonad condition of sea urchins inhabiting the two areas differed significantly. The mean value of the gonad index (GI) for sea urchins from Alekseev Bight was less than half and the maturity index was about twice that of sea urchins from the Verkhovskii Islands. The GI of sea urchins from Alekseev Bight decreased by a factor of 1.5 between 1984 and 1997. Pronounced histopathological changes were found in sea urchin gonads at this station: granular and hydropic dystrophy of oocytes, resorption and a sharp decrease in the number of gametes (in about 20% of the sea urchins, hardly any gametes were found in the gonads), changes in the morphology of accessory cells (hypertrophy, atrophy, and necrosis), and accumulation of lipofuscin in the cytoplasm of accessory cells and oocytes, in the hemal sinuses and mesentery. The suppressed gonad condition of the sea urchin S. intermediusin Alekseev Bight may be a consequence of the unfavorable environmental situation that formed in the bight in the 1980s–1990s. The main negative factor is anthropogenic pollution of Amurskii Bay.     

Synchronized release of medusae from three species of hydrozoan fire corals

 The release of medusae from three hydrozoan fire corals, Millepora dichotoma, M. murrayi and M. platyphylla, was investigated at three sites in southern Taiwan from February 1994 to July 1995. All three species were gonochoristic, and developed and released several batches of medusae between April and May. The duration of open ampulla appearing on the surface of coralla was short, about three months, and could be used to infer the reproductive season of the fire corals between April and May. No obvious lunar cycles of medusa release were found in these species. Medusa release started before dark at approximately 17:00 h and continued for several hours. Males began releasing medusae earlier than females. Synchronization of medusa release between colonies, i.e., the probability of occurring on the same nights, was significantly higher within a species than between different species. Hybridization in nature among the three species is, therefore, unlikely due to segregation in the spawning dates. Moreover, the synchronization within each species was often significantly higher within versus between sites. The free-swimming medusae released gametes within approximately one hour, and the spent medusae lived for a few more hours. Medusae may facilitate fertilization rates as a result of an apparently negatively geotactic swimming response that results in medusa aggregation at the surface. No differences in the sizes of medusae, eggs and sperm were detected among the three species; however, some characteristic differences of medusa nematocysts were found. Accepted: 25 September 1997     

Polyfluorochrome marking slows growth only during the marking month in the green sea urchin Strongylocentrotus droebachiensis

Abstract. Used singly, the fluorochrome tags tetracycline and calcein have yielded important insights into sea urchin biology, especially regarding growth. We present a new method of tagging using sequential fluorochrome markers, as well as a more precise method of quantifying growth. Such polyfluorochromes enable repeated markings that allow measurement of multiple growth points and unique identification of individuals or groups. We marked sea urchins, Strongylocentrotus droebachiensis , with four fluorochromes: alizarin complexone, calcein, calcein blue, and tetracycline. All fluorochromes marked both by injection and immersion. We examined the clarity of the mark produced with low, metabolically scaled doses, and higher doses similar to those that have been previously used. We tested the effect of fluorochromes on survival, growth, jaw size, and gonad size by marking a size range (3.9–44.3 mm in diameter) of urchins with either one or all four fluorochromes. We quantified growth using a nominal diameter, that is a fitted constant, times the cube root of weight, which increased the precision of measurements by a factor of six relative to measured diameter. Growth rate was a decreasing function of diameter except for a growth lag in the smallest urchins. Growth rate data for all sizes were fitted using: gamma distributions; Tanaka functions; and, for larger sizes, straight lines (von Bertalanffy model). All treatments produced clear marks, with higher doses producing more reliably clear marks. Tetracycline marking did not affect growth; other treatments produced only transient slowing of growth in the marking month. Growth rate, survival, gonad production, and jaw weight did not differ between control and treatments during the following 6 months. Thus, polyfluorochromes produce reliable marks that do not significantly affect growth or gonad production.     

Age,growth and reproduction of the Iranian goby, <Emphasis Type="Italic">Ponticola iranicus</Emphasis> (Perciformes: Gobiidae) from the southern Caspian Sea basin

To estimate reproductive biology of Ponticola iranicus Vasil’eva et al., 2015, in Sefidroud River in the southern Caspian Sea basin age, sex ratio, fecundity, oocytes diameter, gonadosomatic, modified gonadosomatic and dobriyal indices were measured. Regression analyses were used to find relations between fecundity and fish size (length and weight), gonad weight, and age. Mature females and males were longer than 46 and 49 mm in total length, +1 in age. The Von Bertalanffy growth models were L _∞ = 23.00 cm (TL), K = 0.21, t ₀ =–0.25 for all specimens. Sex ratio was 1: 1.32 in favor of males. The average egg diameter was 0.96 mm. The spawning period extended from late February to late April. The averages of absolute and relative fecundity were calculated as 536.9 and 81.3, respectively. The absolute fecundity was significantly related to the body length and weight, as well as gonad weight.     

Transitions in morphology, nematocyst distribution, fluid motions, and prey capture during development of the scyphomedusa Cyanea capillata

Like that of most scyphozoans, the ontogeny of Cyanea capillata medusae involves substantive alterations in feeding structures and mechanics. We used video and optical microscopy approaches to quantify these ontogenetic changes in morphology, flow, and feeding of C. capillata medusae. We found that alterations in gross morphology and nematocyst distributions coincided with a shift from prey capture on the manubrium or lappets of ephyrae (bell diameter 0.2-0.4 cm) to capture primarily on the tentacles in adult medusae (diameter >1.0 cm). These changes occurred within a hydrodynamic framework that itself changed due to medusan growth. Viscous forces were important in flows around small ephyrae (maximum Re <10(1)), whereas viscosity was less influential in the inertially dominated flows around adult medusae (Re > 10(2)). The relative timing of these events indicates that ontogenetic processes are closely synchronized with alterations in the hydrodynamic environment within which C. capillata medusae develop.     

Observations on the life history of the belted sandfish,Serranus subligarius (Serranidae)

Synopsis The biology of Serranus subligarius, a typical inhabitant of low limestone reef outcroppings and artificial reefs from North Carolina to Florida and in the northern Gulf of Mexico, was studied on inshore jetties in the northeastern Gulf of Mexico from February 1974 to April 1975. The length-weight relationship was expressed by the equation W = 0.000006L^3.431. Growth was greatest in the first year (43.5 mm SL) and declined in the remaining three years of life (17.3, 10.5, and 7.1, respectively). In individuals larger than 40 mm SL, gammaridean and caprellid amphipods were the most numerous food items but crabs, shrimp, and fishes were the most important food items by weight. In individuals less than 40 mm SL, copepods were the most numerous food item, but gammaridean amphipods and shrimp were the most important items by weight. Two incidents of cannibalism were recorded. The ovotestis of the belted sandfish is composed of two lobes which are broadly united posteriorly, with the testicular tissue restricted to a broad band encircling the posterior region of the gonad. Age-group 1 fish are functional synchronous hermaphrodites. Testicular tissue matures in the fall or winter of a fish's first year (all specimens examined histologically, including those from the nonspawning season, contained flagellated spermatozoa) while ovarian tissue matures in the following spring. Spawning season in 1974 extended from late April or early May to September. Crossfertilization is the usual reproductive mode, although individuals are capable of selffertilization.     

Reproductive cycle and releasing time for increase of resource of adult sea cucumber Apostichopus japonicus released to seed breeding grounds

The reproductive cycle and releasing time for effective increase of resource of adult sea cucumber (Apostichopus japonicus) have been studied in the west coast of Korea. Adult sea cucumbers collected in Seocheon-gun April 2013 for first release and in the uncontaminated Taean-gun area in the west coast of Korea. Divers monthly collected the specimens in the released area from December 2013 to November 2014 in order to investigate the reproductive cycle of A. japonicas in Taean-gun. Random specimens were dissected to examine the gonadal developmental stages and discharge rates of the guts and gonads. The reproductive cycle of A. japonicus in both sexes are classified into the following six successive stages in the Taean-gun: (1) Stage I (recovery stage from December to February), (2) Stage II (early growing stage from February to March), (3) Stage III (late growing stage from March to April), (4) Stage IV (mature stage from April to July), (5) Stage V (partly spawned stage in July), and (6) Stage VI (spent stage from August to November). The estivation period of this species is from July to October in the Taean-gun region while surface water temperature is approximately 20–25.4°C. Thus, the optimum period to easily harvest them is from October to November in the uncontaminated Taean-gun area. It is also the best releasing time because the recovery stage starts from December to February in the Taean-gun region.     

Identification of key nutrients for gonadal development by comparative analysis of proximate composition and fatty/amino acid profile in tissues and eggs of Chinese sturgeon (Acipenser sinensis Gray, 1835)

The present study was conducted to characterize the proximate composition and fatty/amino acid profile in muscle, liver and gonads obtained from farmed male and female Chinese sturgeon (Acipenser sinensis) with gonad development at stage II, and to discern the key nutrients for gonads by comparing the nutrients between tissues and between fish at different gonad stages. Chinese sturgeon were reared in an outdoor circular cement pool at temperatures ranging from 8°C to 26°C, and fed with 70% artificial diets and 30% frozen forage fish at a feeding rate of 0.2%–1.5% body weight according to the water temperature. Three male and three female A. sinensis were sampled for analyses. Results showed that the lipid content in gonads was significantly higher than in other tissues in both males and females (p < .05). The protein content in male and female gonads was significantly lower than that in the muscle (p < .05). Total content of mono‐unsaturated fatty acids (MUFA) in females was significantly higher than in males (p < .05), while the total content of n‐6 PUFA in females was significantly lower than in males (p < .05). Palmitic acid (C16:0) and oleic acid (C18:1n9) were the major saturated fatty acid (SFA) and MUFA, respectively, in both females and males. The contents of C18:2n6, C20:4n6 (ARA), C18:3n3 and C22:6n3 (DHA) in male gonads were significantly higher than in females (p < .05). The contents of ARA, EPA and DHA in gonads were lower, possibly playing a pivotal role in gonad development. Comparing the nutrients of ovaries in broodstocks at stages III and IV and the eggs at stage IV, the present study suggests that the lipid and fatty acid profile in fish is vital to the gonad development and that proper improvement of lipid nutrition in the broodstock diet to provide sufficient energy and essential fatty acids would be beneficial for the gonad development of Acipenser sinensis.     

Cytomorphology of female and male gonads in Antarctic toothfish <Emphasis Type="Italic">Dissosctichus mawsoni</Emphasis> (Nototheniidae) from the Ross Sea in the summer period

Results of histological analysis of gonads of female and male Antarctic toothfish Dissostichus mawsoni caught in the Ross Sea of the Pacific sector in the period of Antarctic summer (December–February) 2004–2005 are presented. Morphological indices and index of gonad maturity are described and ecological criteria of assessment of maturity stages of ovaries, cytological indices of oocytes, and the type of toothfish oogenesis are determined. It was established that in the period of fishing Antarctic toothfish, females and males with gonads at maturity stage III dominate. Ovaries contain two groups of oocytes of the period of trophoplasmatic growth and large oocytes of the nearest spawning season that comprise the smallest proportion of total sex cells. In the testes of two male toothfish, the primary fusion of renal and generative tissues was revealed. It is suggested that the termination of gonad maturity of toothfish takes place from March to April, and spawning takes place from June to August.     

Reproductive biology of a Gobiid fish Oxyurichthys tentacularis (Valenciennes, 1837) inhabiting Ashtamudi Lake,S. India

Reproductive traits of Oxyurichthys tentacularis, a most demanded fish in Ashtamudi Lake, S. India were studied from samples collected using gill net, cast net and dip net during 2013–2015. Sexes were separated by observing the urogenital papilla in males and the gonads. Five maturity stages were identified by examining the gonads. Though advanced maturity stages were encountered throughout the year, higher preponderance of ripe gonads was discernible during August to November and February to April. Gonadosomatic indices indicated same trend in both sexes. The length at first maturity was 86.67 mm in males and 80.17 mm in females. The absolute fecundity ranged from 5,112 (102 mm TL) to 52,431(175 mm TL). Fecundity established linear relationships with total length, body weight and ovary weight. Ova diameter studies revealed that spawning takes place in batches at regular intervals and the species is a multiple spawner. The ratio of males to females was found to be 1:0.7 (χ² = 10.8; p < 0.05). The pooled average for the whole period showed a perceptible dominance of male population in all of the months except in January (χ² = 2.3; p > 0.05) could be observed.     

Observations on the age, growth, reproduction and food of the roach Rutilus rutilus (L.) in two rivers in southern England

Scales and opercular bones from 632 roach from the River Stour were used for age and back-calculated growth determinations. The scales had clearer inner annuli but operculars clearer outer annuli in fish more than nine years old. The annuli were laid in late May or early June at the beginning of the growth period. Growth was minimal between November and April. Roach from both rivers grow faster than those in most other European waters. Female roach grow faster than males; River Frome roach faster than those from the Stour. Spawning occurred in May and elaboration of gonads between September and May. Immature roach have an annual cycle in condition with a maximum in June and a minimum in early Spring. The condition of mature females is affected by the gonad cycle. The fecundity of Stour roach is represented by the formula: log egg number=4.43 log length (mm)—1.69. Approximately half of the Stour males attained sexual maturity at age III and most of the rest by age IV. Half of the females were mature at age IV and the remainder by age V. Both brood success and growth rate varied from year to year but independently of one another. Most Stour roach ate aquatic insect larvae and molluscs but algae were more frequent in the diet of larger fish.