Ovarian development of a river catfish Hemibagrus nemurus (Valenciennes, 1840) in captivity

Hemibagrus nemurus is a riverine catfish with high economic and nutritive values. Investigations on ovarian development of this fish were carried out to determine the mode of ovarian development and describe the oocyte developmental stages. Histological studies were done on ovaries using light microscopy and scanning electron microscopy. Fish were sampled monthly for a period of six months (August 2009 to January 2010). The mean oocyte diameter (OD) ranged from 871 ± 161.41 μm to 1,167 ± 26.77 μm and the highest OD was in November. Oocyte size-frequency distribution showed a polymodal distribution. The mean gonadosomatic index (GSI) ranged from 1.14 ± 0.87% to 7.06 ± 1.40% and highest GSI was in November. The ovaries exhibited three phases of oocyte growth, which were primary growth, secondary growth and maturation phases. Based on histological criteria, the oocyte developmental stages were divided into seven stages as chromatin nucleolar, early perinucleolar, late perinucleolar, cortical alveolar, vitellogenesis, mature oocyte and germinal vesicle migration stages. All the seven stages of oocyte development were observed in the ovaries. Oogonia were always present throughout the developmental stages. The ovaries had more than two stages of oocyte development. This is the first report on the mode of ovarian development of H. nemurus. These findings indicated that H. nemurus has asynchronous mode of ovarian development and is capable of spawning several times in a year under favourable conditions.     

Annual Variations of Gonadotropin Content and Ovarian Development of Feral Female Catfish, Silurus asotus, in Central China

The Japanese catfish Silurus asotus is widely distributed throughout the freshwaters reservoirs, lakes and rivers of China, Korea and Japan, and is a commercially valuable aquaculture fish in some regions of China and Japan. We studied seasonal variations of gonadotropin (GtH) content of the plasma and pituitary as well as ovarian development. Plasma GtH titres increase in April in the Pearl River and in May in the Liao River in central China. Annual cycles of plasma GtH levels in both rivers are the same, with a gradual decrease after ovulation with the lowest values observed in September (in the Liao River) or October (in the Pearl River). Plasma GtH levels increase gradually in the early stages of ovarian development, with the highest values observed during the late stages of development, and with the lowest GtH titres observed during ovarian regression in both rivers. GtH content of the pituitary remained very high through the spawning period, with the highest titres observed in March in the Liao River, and in July in the Pearl River. As with plasma GtH, the lowest concentrations of pituitary GtH were observed during stages when the ovary was regressed. We analyzed the relationships between plasma and pituitary GtH and reproductive conditions, such as gonadosomatic index (GSI), hepatosomatic index (HSI), oocyte diameter (OD) and oocyte weight (OW). The results indicate that annual changes of GtH content of the plasma and pituitary paralleled GSI, OD and OW, but were negatively correlated with HSI in feral female catfish.     

Changes in ovarian development and plasma levels of sex steroid hormones in the wild female Japanese sardine (Sardinops melanostictus) during the spawning period

In order to clarify the spawning pattern of Japaneses sardine ( Sardinops melanostictus ) during the spawning period, changes in ovarian histology, frequency distributions of oocyte diameter and plasma levels of oestradiol-17β (E₂) and 17 a ,20β-dihydroxy-4-pregnen-3-one (17 a ,20β-diOH-P) were examined in female fish captured in the region off Kyushu and Shikoku in Japan. With the development of the ovary, the gonadosomatic index (GSI) increased gradually and the size of oocytes became larger. When the GSI exceeded 13, the translucent hydrated eggs began to dominate and ovulation subsequently occurred. After ovulation, GSI decreased to less than 3. Post-ovulatory follicles were found only in the lower GSI ranges and atretic oocytes were always observed in the ovary. Plasma E₂ levels increased along with ovarian development but decreased after completion of yolk accumulation. On the other hand, 17 a ,20β-diOH-P showed the highest level just before and after ovulation. Ovarian histology and hormonal profiles suggest that the sardine spawns repeatedly during the spawning period. Based on the concentration of 17a,20β-diOH-P, the female Japanese sardine was estimated to ovulate before the middle of the night.     

拟目乌贼卵子发生与卵巢发育

为了丰富拟目乌贼(Sepia lycidas)生物学资料, 为人工育苗与养殖提供理论依据, 采用解剖学和组织学的方法, 对水泥池养殖条件下拟目乌贼卵子发生和卵巢发育进行了研究。结果表明: 经过6个月水泥池养殖, 平均体重为256.34 g, 最大体重达到457.08 g, 个别发育成熟, 绝大部分未达性成熟。卵子发生不同步, 根据细胞形态、细胞大小、滤泡细胞形态和卵黄形成情况可分为卵原细胞阶段(卵原细胞期)、原生质生长阶段(无滤泡期、单层滤泡期和双层滤泡期)、间质生长阶段(滤泡内折早期、滤泡内折中期和滤泡内折晚期)和营养质生长阶段(卵黄发生早期、卵黄发生晚期和成熟期), 共4个阶段10个时期。卵巢发育根据外观形态、性腺指数变化和切面上各期细胞所占的比例, 可分为形成前期、形成期、小生长期、大生长期、成熟前期和成熟期6个时期。拟目乌贼繁殖周期为一年。       

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.     

Spawning season, ovarian development and fecundity of female Trichomycterus corduvense (Osteichthyes, Siluriformes)

We studied female reproductive biology of Trichomycterus corduvense. The study was carried out in the Anizacate River (Córdoba, Argentina). Samples were collected throughout one year on a monthly basis. Seven oocyte phases were identified. Five ovarian stages were described based on the macroscopic analysis of the oocyte phases. The spawning season for the species ranges from October to February; it was determined based on variations in GSI and the existence of mature females. The dynamics of oocyte development of T. corduvense, indicated the asynchronism of maturation. The correlation coefficient between fecundity and the individual weight was very low. Therefore, we suggest that this coefficient cannot be used to predict T. corduvense fecundity.     

The multiple spawning pattern of weakfish in the Chesapeake Bay and Middle Atlantic Bight

Weakfish Cynoscion regalis were collected from commercial fisheries in the Chesapeake Bay and the Middle Atlantic Bight (n=4380) during 1989–1992 and their reproductive biology assessed using the gonadosomatic index, macroscopic gonad stages, oocyte diameter distributions, microscopic whole oocyte analysis and histology. Sex ratios were approximately 3:1, females to males, in 1990–1992. Most fish (90%) attained sexual maturity by age 1 and at a small size. Estimated mean length at first maturity was: 164mm total length (TL) for males, and 170 mm TL for females. Weakfish spawn within the Chesapeake Bay, as far north as the Virginia/ Maryland border. Although spawning occurred during May–August and gonad development and initiation of spawning was synchronous, cessation of spawning was asynchronous. There was no indication that older fish exhibited a more extended spawning season than younger fish. Weakfish are multiple spawners with indeterminate fecundity. Oocyte development is asynchronous with oocytes of all stages being present in developed ovaries. Because of the complex and dynamic weakfish ovarian cycle, typical methods of assessing reproduction, such as the GSI and macroscopic gonad stages, are inadequate for this species if not used in conjunction with more detailed methods such as histology.     

Ovarian development and histological observations of threatened dwarf snakehead fish,Channa gachua (Hamilton, 1822)

Channa gachua were monthly sampled throughout a year and the histological analysis of their ovaries was done to determine the changes occurring in ovarian development. Based on histological examination of the ovaries, the oogenic process of C. gachua undergoes distinct cyclic and seasonal morphological changes. Five different developmental stages were identified under three major categories: pre-spawning (immature, maturing, mature), spawning (ripe-running) and post-spawning (spent). The peak spawning period of C. gachua was noticed during December - February. The gonadosomatic index (GSI) and ova diameter ranged from 0.79 to 3.61% and 543–1123 μm respectively. The highest mean GSI (3.61 ± 0.16) and oocyte diameter (1123 ± 55 μm) were observed in December indicating that during this month the gonadal development reached maturity.     

Spawning behaviour of barred spiny eel,Macrognathus pancalus,in the River Gomti,India

The present study investigated the spawning behaviour of the spiny eel, Macrognathus pancalus, and its relationship with the environment (photoperiod and temperature). The results show that M. pancalus breeds during February to September with peak spawning during February/March and July/August, indicating two main breeding periods. Initiation of breeding occurs during increasing day lengths in early spring (February/March), and regression during decreasing day lengths in autumn (September/October). The breeding status confirmed by gonadosomatic index (GSI) and ovarian histology showed six stages of ovarian maturation (viz. stage I: chromatin nucleaolar; II: perinucleolar; III: cortical alveolar; IV: vitellogenesis; V: ripe; and VI: partially spent), with predominance of one or more stages at a particular time of the year. Males also followed a similar seasonal pattern in gonadal maturation as reflected by their GSI. Results show that M. pancalus is a seasonal breeder with bimodal spawning activity. The breeding pattern suggests an influence of prevailing day length conditions at this latitude.     

Annual Cyclical Changes in the Histological Features and Surface Ultrastructure in Ovaries of the Freshwater Featherback Notopterus notopterus (Pallas, 1769)

The feather back, Notopterus notopterus is an important food fish. Its ovary is an extremely dynamic organ and the oocytes present an asynchronous development. Variations in ovary weight, GSI, diameter of oocytes were studied in different months of the year in this fish. Different developmental stages of female germ cells were identified on the basis of histological and ultrastructural characteristics in the ovary of N. notopterus (Pallas). In the present investigation the oocyte development of N. notopterus was divided into five stages (oogonia, perinucleolar oocyte, cortical alveolus, yolk granules stage and mature oocyte). The cytophysiological features like vitellogenesis, chorion formation and atresia of some follicles were also studied in the present investigation. The seasonal changes in the ovary have been described according to the variations in gonadosomatic index and the cytological changes of the female germ line cells.     

Role of the tidal cycle in the gonadal development and spawning of the tropical wrasse Halichoeres trimaculatus

Many wrasses on coral reefs exhibit daily spawning that peaks around daytime high tides. In this study, we examined tidal-related ovarian development in the threespot wrasse, Halichoeres trimaculatus, a species common on coral reefs in the Indo-Pacific Ocean. When the fish were collected in the morning at different tidal phases, the gonadosomatic index (GSI) and ovarian histology changed; concomitant with increases in GSI towards high tide, a clutch of the most advanced oocytes developed from vitellogenic to maturation stages. Ovulated eggs and post-ovulated follicles (POF) existed in most ovaries around high tide, but only POF remained around ebb tide, suggesting that spawning occurred during or after high tide. We noticed that tidal-related spawning was considerable in the morning and that most ovaries collected on the afternoon high tide exhibited post-spawning features. This suggests that certain labrid species possess plasticity with regard to their spawning time and utilize potent environmental cues to ensure their reproductive success. When pieces of ovary were incubated with precursor steroids, high conversion of testosterone to 17beta-estradiol occurred during high and ebb tides, while that of 17alpha-hydroxyprogesterone to 17alpha,20beta-dihydroxy-4-pregnen-3-one and 17alpha,20beta,21-trihydroxy-4-pregnen-3-one was observed during low and flood tides. Incubation of pieces of ovary with human chorionic gonadotropin resulted in similar fluctuations in the steroid hormones with tidal phase. Production of these steroid hormones correlated with oocyte development in the ovaries and was probably regulated by gonadotropin. These results demonstrate that the daily cycle is fundamental for oocyte development, and that the tidal cycle is superimposed on this process.     

Effect of 17β-Estradiol on Growth of Oocytes in Cultured Ovarian Fragments of the Starfish, Asterina Pectinifera

The development of growing oocytes of the starfish, Asterina pectinifera , was divided into five stages according to their histological features. Specimens collected monthly from Rishiri Island throughout a year were used. The effect of 17 β-estradiol on oocyte growth was investigated. When ovarian fragments taken from April females were cultured in artificial seawater containing Medium 199 and streptomycin sulfate for 3 days, oocytes within such fragments did not show any changes in diameter. However, when similar ovarian fragments were cultured in the presence of 10⁻⁵M 17 β-estradiol, the oocyte diameters increased significantly. It is concluded that 17 β-estradiol enhances the growth of starfish oocytes in cultured ovarian pieces.     

Reproductive cycle of gilt sardine,Sardinella aurita,Valenciennes 1847, in the eastern middle Adriatic Sea

The annual reproduction cycle of gilt sardine, Sardinella aurita, based on gonad maturity stages, gonad weight and gonadosomatic index was the subject of this study. A total of 2033 gilt sardines (983 males, 1021 females and 29 undetermined) were analysed. Fish were collected monthly from commercial purse seiners between November 2007 and January 2009 in the eastern middle Adriatic Sea (mesh size 8 mm/bar length/; sampling: five boats per month). Based on the monthly evolution of gonad maturation stages, gonad weights and gonadosomatic index, the peak spawning season was determined to be from June to August. Variations in sea surface temperature (SST) coincided with monthly variations of the gonadosomatic index. Highest monthly average values for both analysed parameters were recorded in July (GSI = 3.38; T = 26.5°C). Fifty per cent (L₅₀) of males and females reached sexual maturity at TL 15.8 cm and at 16.6 cm, respectively. Absolute fecundity ranged from 8458 to 48 032 (mean 34 565 ± 10 310), whereas relative fecundity was from 171 to 722 (mean 385 ± 104.35). Mean value of the oocyte size was 0.53 ± 0.10 mm.     

Ovarian cycling of tilefish, Lopholatilus chamaeleonticeps Goode and Bean, from the South Atlantic Bight, U.S.A.

Reproductive cycling and oocyte development were examined for female tilefish, Lopholatilus chamaeleonticeps Goode and Bean, captured in the South Atlantic Bight, U.S.A. A total of 752 female tilefish was collected during 15 sampling periods from May 1982 to December 1983. Reproductive cycling was quantified using four techniques: gross visual estimation of ovarian stages, histological examination of ovaries, follicle diameter measurements, and an ovarian index. The relative accuracies of these techniques also were evaluated. All four methods indicated that L. chamaeleonticeps was capable of spawning from March to June. Most spawning occurred between April and June. Ovarian development was positively correlated with the change in daylength. Follicular development was asynchronous, which is characteristic of multiple spawners. Folliculogenesis was similar to that in most oviparous teleosts.     

Ultrastructure of oogenesis in the bluefin tuna, Thunnus thynnus

Ovarian ultrastructure of the Atlantic bluefin tuna (Thunnus thynnus) was investigated during the reproductive season with the aim of improving our understanding of the reproductive biology in this species. The bluefin, like the other tunas, has an asynchronous mode of ovarian development; therefore, all developmental stages of the oocyte can be found in mature ovaries. The process of oocyte development can be divided into five distinct stages (formation of oocytes from oogonia, primary growth, lipid stage, vitellogenesis, and maturation). Although histological and ultrastructural features of most these stages are similar among all studied teleosts, the transitional period between primary growth and vitellogenesis exhibits interspecific morphological differences that depend on the egg physiology. Although the most remarkable feature of this stage in many teleosts is the occurrence of cortical alveoli, in the bluefin tuna, as is common in marine fishes, the predominant cytoplasmic inclusions are lipid droplets. Nests of early meiotic oocytes derive from the germinal epithelium that borders the ovarian lumen. Each oocyte in the nest becomes surrounded by extensions of prefollicle cells derived from somatic epithelial cells and these form the follicle that is located in the stromal tissue. The primary growth stage is characterized by intense RNA synthesis and the differentiation of the vitelline envelope. Secondary growth commences with the accumulation of lipid droplets in the oocyte cytoplasm (lipid stage), which is then followed by massive uptake and processing of proteins into yolk platelets (vitellogenic stage). During the maturation stage the lipid inclusions coalesce into a single oil droplet, and hydrolysis of the yolk platelets leads to the formation of a homogeneous mass of fluid yolk in mature eggs.     

Maturation-related variations in prostaglandin and fatty acid content of ovary in the kuruma prawn (Marsupenaeus japonicus)

Total lipid, fatty acids and prostaglandins (PGF(2 alpha) and PGE(2)) in the ovary of kuruma prawns (Marsupenaeus japonicus) were measured during ovarian development. The level of ovarian total lipid increased with an increase in the gonad-somatic index (GSI). No significant difference was found in fatty acid composition among different stages of ovarian development. However, the content of arachidonic acid (precursor of PG(2)), but not eicosapentanoic acid (precursor of PG(3)), was significantly lower at stages I and II than at stage V (P<0.01). When ovarian PGF(2 alpha) and PGE(2) levels were plotted against GSI, no correlation was found in either PG. However, in terms of ovarian developmental stages, the level of ovarian PGs was high (approx. 20 pg/mg) at stage I, followed by marked decreases at stages IV and V (PGF(2 alpha), P<0.01) and stage IV (PGE(2), P<0.01). These results suggest that ovarian PGs and arachidonic acid are deeply involved in ovarian maturation in kuruma prawns.     

Ovarian development in the Amazonian red discus, Symphysodon discus Heckel (Osteichthyes: Cichlidae).

The Neotropical red discus fish, Symphysodon discus, originates from the Amazonian basin and has a discoid body. Although this species is popularly used in aquaria and is exported as an ornamental fish, it has not been intensively studied. The purpose of this work was to study the morphological and histological aspects of the ovarian development in the red discus. Forty females of S. discus of varying body sizes and different stages of gonadal development were used in this study. The ovaries were weighed and examined macroscopically in order to observe the maturation stages. Histological staining of hematoxilin-eosin was used for microscopic observations of the ovaries. Macroscopic observations showed immature, maturing, mature and partially spent stages of ovarian development. Microscopic examination of the ovaries revealed five stages and five phases of ovarian development. The ovaries of the mature females showed all the different phases of oocyte development, indicating the multiple spawning habit of this species.