Ovarian dynamics and fecundity regulation in blueback herring,Alosa aestivalis,from the Connecticut River,US

We analyzed ovarian dynamics of anadromous blueback herring, Alosa aestivalis, in Connecticut River with the principal aim of exploring oocyte recruitment and how it shapes the fecundity pattern. We examined the oocyte release strategy and analyzed spawning cyclicity by linking oocyte growth to the degeneration of postovulatory follicles. Females were accordingly classified as pre-spawners, early and late active spawners, and oocyte recruitment intensity was compared among the different spawning phases. Oocyte recruitment occurred continuously and in parallel with spawning activity, a pattern which is diagnostic of indeterminate fecundity. However, both fecundity and oocyte recruitment intensity progressively decreased (tapered) throughout spawning, until the ovary was depleted of vitellogenic oocytes. There was no massive atresia of vitellogenic oocytes at the end of the spawning season, which is atypical of indeterminate spawners. We propose that tapering in oocyte recruitment and fecundity is an adaptation to the high energetic expenditure of the upstream spawning migration.     

Reproductive strategy of the European perch,Perca fluviatilis Linnaeus, 1758 (Osteichthyes: Percidae) in the Anzali wetland,southwest Caspian Sea

Temporal variation in reproductive traits of geographically distributed fish is supposed to take place in response to the spatial and environmental variations. With regard to the wide distribution of the European perch in the northern hemisphere, important reproductive traits such as the initiation and duration of the spawning activity are likely to vary in different latitudinal gradients. In this study, reproductive biology of the European perch, Perca fluviatilis, is described, based on 324 specimens caught in the Anzali wetland (southwest Caspian Sea) between June 2008 and May 2009. The gonadosomatic index, oocyte frequency distribution and histological examination suggested a long vitellogenic process (October to February) and a short spawning season (January and February). The size‐frequency distribution of the oocytes showed that this perch is a species with group‐synchronous ovarian development. Ovarian development occurred only in one clutch of oocytes (700–900 μm oocyte diameter) with no indication of maturation of any subsequent clutch in the spawning season. The average of (realized) fecundity (±SD) was estimated to be 16177 ± 5846 eggs in late vitellogenic stage, which was lower than the potential fecundity (17188 ± 6917 eggs). Histological examination of the gonads revealed the existence of atretic oocytes in early vitellogenic stages (October and November). This investigation highlights the temporal variation in the initiation and duration of the reproductive activity of the European perch in this region compared to other geographical regions. The results emphasize the necessity of specific temporal management in fishing of European perch based on spatial differences in reproductive biology.     

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.     

Reproductive guilds (maturation,spawning frequency and fecundity) in the black pomfret,Parastromateus niger (Carangidae) in the Kuwaiti waters of the Arabian Gulf

Oogenesis, oocyte maturation pattern, spawning rhythm, spawning frequency, batch fecundity and oocyte diameter–frequency distribution of the black pomfret, Parastromateus niger (Bloch, 1795) in Kuwaiti waters were investigated from October 2003 to September 2005, using histological and morphological methods. The process of development is divided into four major phases: (i) primary growth phase; (ii) secondary growth phase; (iii) maturation phase; and (iv) spawning phase, followed by the regressed phase. Development of the yolky oocyte is an asynchronous process resulting, by the time of oocyte maturation, in a clear differentiation between a ready batch of oocytes (ready for spawning) and a reserve pool. Consequently, P. niger is capable of spawning multiple times throughout the reproductive season. Spawning frequency estimates, based on final oocyte maturation (FOM) method indicated that the species spawns once every 2.8 days during an 8‐month spawning season lasting from February to September, with a potential annual number of 22.4 spawns. Batch fecundity (BF) (2132–2001 648, mean 406 010 eggs), was significantly positively related to both standard length (SL) (P < 0.05) and ovary‐free body weight (OFBW) (P < 0.05), both parameters being good predictors of BF (r² = 30.8% for SL, from 22 cm onwards, and r² = 29.6% for OFBW, from 129.5 g onwards). No significant differences in monthly BF were found throughout the spawning season. Relative batch fecundity was 336 eggs/g OFBW; thus, estimate for potential annual relative batch fecundity was 7526 eggs g^?1 OFBW. The oocyte diameter–frequency distribution analysis revealed a multimodal distribution (at 100–200, 300–400 and 500–700 μm), confirming the evidence of multiple spawning.     

Reproductive patterns of blacktail comber (Serranus atricauda,Serranidae) from south-west Portugal seamounts

The knowledge of the reproductive strategy is essential for the comprehensive understanding of the population dynamics of any fish species. This study intends to define the spawning season, verify the type of fecundity regulation and estimate relative annual fecundity for Serranus atricauda inhabiting the south-west of Portugal seamounts (Gorringe, Ampère and Lion). Monthly samples, between September 2010 and December 2011, were obtained from commercial vessels. This species is synchronously hermaphroditic, and mature individuals were found all year round, with gonadosomatic index peak from February to September. No clear relation between hepatosomatic index and Fulton’s condition factor and gonadal development was found, and therefore, it is probable that reproductive success depends more on environmental conditions and food availability during the spawning season than on body energy reserves. No gap exists between pre-vitellogenic and vitellogenic oocytes and the oocyte size-frequency distribution during the main spawning season show no dominant cohort progressing through time. The number of standing stock of advanced vitellogenic oocytes showed an increase trend along the spawning season decreasing only at its end and the relative intensity of α-atresia was always low throughout this period with an increase towards the end. All these criteria corroborate the indeterminate fecundity type assigned to S. atricauda in previous studies. Mean relative annual fecundity estimated was 5,655 ± 4,321 oocytes per gram of gutted weight.     

Determination of batch fecundity in Uranoscopus scaber Linnaeus, 1758 from the Aegean Sea, Turkey

This work focuses on reproductive biology aspects of Uranoscopus scaber from the coast of the Aegean Sea. In total, 175 U. scaber specimens were collected in Izmir Bay using trawl nets from January to December 2005. The reproduction period according to gonadosomatic index (GSI) values extents from March to September, with a peak in May (6.32 ± 1.2). Oocyte diameters taken from 59 mature gonads ranged from 62 to 1860 μm. Maximum batch fecundity (BF) was 58091 (mean: 11556 ± 1445) in large oocytes in May, and 8408 (mean: 2821 ± 945) in hydrated oocytes in September. The BF increased with total length and body weight, excluding the ovaries. Total length (TL)–BF relationships and fish weight–BF relationships were BF = 0.0034TL^4.6248 (r = 0.47) and BF = 59.166W?3101 (r = 0.49), respectively, according to the oocyte size frequency method. There was a linear relationship between BF and fish size.     

Comparative oocyte morphology and fecundity of five characid species from São Francisco River basin,Brazil

The morphology of vitellogenic oocytes and the batch fecundity of five tropical forage species belonging to the family Characidae, were studied in 104 late‐maturing ovaries. Significant morphological differences between vitellogenic oocytes and ovarian follicles were found. The lowest batch fecundity values were recorded in Hemigrammus marginatus (480 ± 163) and Orthospinus franciscensis (1701 ± 562), which were the smaller species in terms of total length, body weight and oocyte diameter. The highest batch fecundity value was observed in Tetragonopterus chalceus (8384 ± 3944) having the highest GSI and oocyte diameter. Batch fecundity and gonad weight was highly correlated followed by body weight and total length. Relative fecundity was estimated per unit total length, body weight and gonad weight. The wide variation in fecundity observed between the specimens and the species analysed is possibly related to the multiple spawning reproductive strategy of these fishes. Since T. chalceus have higher values of batch and relative fecundity, it is concluded that this species has a higher reproductive potential than the other forage species studied.     

Reproductive biology of hardhead catfish Ariopsis felis: evidence for overwintering oocytes

Hardhead catfish Ariopsis felis are a common marine catfish in the coastal waters of the Gulf of Mexico (GOM). The low economic value of this species has depressed interest and research, and although the species is known for its extremely low fecundity and large oocytes, little else is known about this catfish species. A total of 1230 samples across all months of the year from 2016 to 2018 resulted in 681 females, and analysis of gonado-somatic index (I_G) revealed 1% to be a clear cut-off indicating maturity. Females are considered capable of spawning from April to June when I_G averaged 4–8%. Both atresia and post-ovulatory follicles were present in July, suggesting that spawning ends in July in the northern GOM. The 1% I_G cut-off was used to designate maturity, and from that an L₅₀ of 253 mm was estimated. Batch fecundity from 41 females estimated a mean batch size of 36 oocytes. Perhaps the most interesting finding was the presence of secondary growth stage oocytes (e.g., cortical alveoli) from July through November, well outside the spawning capable period. Furthermore, 78% of females had some early vitellogenic oocytes present during the non-spawning season, and the distribution of these relatively large (2–5 mm) oocytes did not change over time. The results here are not only important as reproductive biology information for a common and abundant species, but also present interesting and unusual patterns of non-spawning season oocyte development that is not commonly seen in Western Hemisphere subtropical fish species.     

Timecourse of oocyte development in saithe Pollachius virens

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre‐spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October–early November, at a leading cohort size (C_L) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre‐spawning, but atretic re‐absorption of remnant oocytes containing yolk granules was found in all females immediately post‐spawning. As expected, concentrations of sex steroids, oestradiol‐17β (females), testosterone (both sexes) and 11‐ketotestosterone (both sexes), increased pre‐spawning before dropping post‐spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post‐ovulatory follicles were visible in histological sections from female gonads 9–11 months post‐spawning, but then disappeared. Spawning commenced around a C_L of c. 750 µm (700–800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, L_T = 60 cm). Spawning lasted from 13 February to 29 March.     

The influence of feeding regime on sexual maturation, fecundity and atresia in first-time spawning turbot

Exposure of adolescent turbot Scophthalmus maximus to low rations during vitellogenesis, covering the 4 months immediately prior to spawning, led to a drop of 70% in mean ovary weight, and was associated with poor growth of the vitellogenic oocytes or, in a third of cases, the absence of vitellogenic oocytes. Exposure to low rations during the recruitment of vitellogenic oocytes, 4–8 months prior to spawning, produced a more variable response. A few of these females produced well-developed vitellogenic oocytes, but in most, vitellogenic oocytes were absent or only poorly developed and in some cases there was a high incidence of atresia. Exposure to intermediate rations throughout oocyte recritment and vitellogenesis also depressed oocyte development. In maturing females the number of non-atretic vitellogenic oocytes (relative potential fecundity) averaged 998 per g of somatic body weight of fish at the start of the spawning season in mid-June. Maturation of the males was not significantly influenced by the dietary regime. The small size of the testes and the low levels of milt production, even in fish fed high rations immediately prior to spawning, showed that reproductive investment in males was much lower than in females.     

Spawning frequency, fecundity, egg weight and spawning type of silver pomfret, Pampus argenteus (Euphrasen) (Stromateidae), in Kuwait waters

Silver pomfret, Pampus argenteus, were collected by fishing with drift gillnets on one spawning ground in Kuwait waters during 1998–2000. Fish size frequency, sex ratio, maturation cycle, spawning frequency, fecundity and egg weight were assessed. The length–weight relationship differed between sexes whereby females were significantly bigger than males. Spawning started in mid‐May and continued until early October. During this time the water temperature ranged from 26.0 to 32.8°C, salinity was ? 39.0‰ and water depth ranged between 5 and 12 m. Large females spawned earlier than young spawners and the overall percentage of males during the spawning period was 70.3%. Spawning occurred after 13.00 h, with peak spawning between 15.00 and 18.00 hours during outgoing tide. Mean daily spawning frequency amounted to 63.2%. Spawning activity was found to be associated with the lunar cycle and spawnings were concentrated during the first and third quarters of the moon period, indicating a semilunar reproduction cycle. It was concluded that a female would spawn at least six times during the season. No change was observed in relative fecundity during the peak spawning season (June–August). Average relative batch fecundity was 176.3 eggs g^?1 somatic weight (SW), corresponding to a relative total fecundity of 1058 eggs g^?1 SW, which is 1.5 times higher than estimates obtained from counting the standing stock of oocytes. Bigger fish produced heavier eggs and the egg weight decreased as the spawning season progressed. Based on gonadal cycles, oocyte size frequency distribution and total fecundity, we concluded that silver pomfret is a multiple batch spawner with indeterminate fecundity.     

Aspects of the reproductive biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

The annual cycles of gametogenesis, spawning and fertilization biology were investigated in the South African polychaete Arenicola loveni loveni (Kinberg, 1866). Sexes are strictly separate (gonochoric) with a 1:1 ratio and gametogenesis takes place in the coelomic cavity. Reproduction is iteroparous and occurs during a synchronized annual epidemic spawning event during the summer months of February or March, which lasts no longer than 2 weeks at around the time of highest annual seawater temperatures. A slight inter-annual variation in spawning time was observed between 2003 and 2004. Annual fecundity was estimated as 311,200 (± 82,040 standard deviations) oocytes per female per year. Oocytes are arrested at prophase I of the first meiotic division and require a maturation step prior to spawning and subsequent fertilization. Mean spawned oocyte diameter was 141.16 μm ± 0.43 SE. Sperm develop as morulae in the coelomic cavity and also require a maturation step prior to spawning. Spawning can be achieved by injection of prostomial homogenate in both males and females and by injection with 8,11,14- e cosatrienoic acid for males and can be delayed by temperature manipulation. Oocyte maturation and sperm maturation can be induced in vitro by incubating in prostomial homogenate.     

Aspects of the fecundity of the feral catfish,Clarias macrocephalus (Gunther), population obtained from the rice fields used for rice-fish farming,in Malaysia

The catfish, Clarias macrocephalus, harvested from the irrigated rice fields of Malaysia, exhibited spawning activities that are influenced by water level management. The multiple spawning potential of the fish is negated by declining water level and the fish spawned only once per growing season. Although oocyte development started in conjunction with water level increase, subsequent oocyte development did not take place due to low water level. Absolute and relative fecundity also decreased with declining water level, however, mean relative fecundity is relatively constant (17.6–53.7 oocytes g^–1 body weight) and not related to body size. Absolute fecundity ranged between 785 to 14066 oocytes female^–1, whereas relative fecundity is between 7.1 to 83.5 oocytes g^–1 body weight, respectively.     

Ripening of the oocyte of the river lamprey (Lampetra fluviatilis L.) after river entry

River lampreys (Lampetra fluviatilis L.) enter rivers for spawning with their gonads in the final stages of maturation, however the oocytes continue to develop until the spawn. This study was undertaken to depict detailed changes in the oocytes in the period approaching the spawn, using metric analysis and to look for atresia to determine if the time period influences the final fecundity. The study was performed on 37 females caught between October and May in the Rega River, north‐western Poland. Mid‐part sections of fixed ovaries were stained with Heidenhain haematoxylin and PAS. Ten cell structures of the oocytes were measured under light microscope with the aid of a computer image analysis programme. In the autumn, when the first lampreys entered the river, the nuclei of the oocytes were in the polar position. With the approaching mating season many oocyte structures changed significantly. Statistically significant (P < 0.001, Mann–Whitney U‐test) was the increase in oocyte size (up to 1.06 × 0.78 mm in morphometric measurement), enlargement of the yolk platelets (f.a. 8.0 × 5.1 μm), elevation of theca over the chorion followed by the accumulation of glycoconjugates (f. a. 29.2 μm), growth of the zona granulosa at the vegetative pole (f. a. 24.2 μm), and increase in the thickness of the chorion at the animal pole (f. a. 11.1 μm). Other statistically significant changes (P < 0.05 and P < 0.01, Mann–Whitney U‐test) included a decrease in the width of the cortical cytoplasm band (f. a. 20.5 μm), decrease in the ratio of the distance between the nucleus and cell membrane and the long axis of the oocyte (f. a. 7.6 μm), and increase in the thickness of the chorion at the vegetative pole (f. a. 6.0 μm). No statistically significant changes in the area of the nucleus and diameter of the cortical alveoles were noted. Beginning with the lamprey entering the river until the spawn, the oocytes undergo significant growth and maturation. In this period the fecundity of the lamprey decreased only slightly, as atresia was observed sporadically in the ovaries.     

Reproductive biology of Galaxias maculatus (Jenyns 1842) in the Río Ovando,a high‐latitude environment in southernmost Patagonia,Argentina

This study establishes the reproductive cycle, batch fecundity and oocyte diameter of a diadromic population of the puyen, Galaxias maculatus, in the Río Ovando, Tierra del Fuego, (54°S), at the southernmost limit of its distribution. Given the short ‘favourable season’ in relation to other populations of the species (in terms of temperature, photoperiod and food availability), the study also explores the trade‐offs between feeding and oocyte production and between phases of growth and reproduction. The reproductive cycle was analyzed by the monthly evolution of the proportion of gonadal maturity stages (determined from microscopic examination of the gonads). Oocytes were measured using a micrometric ocular scale and classified by diameter and morphological characteristics; absolute fecundity was established as the total number of hydrated oocytes per ovary. The studied population exhibits a repetitive spawning strategy, given the coexistence of post‐ovullatory follicles and hydrated oocytes in histological sections and the presence in ripe ovaries of an intermediate cohort of yolked oocytes ready for hydration. Individual fecundity is lower (1422 ± 422 oocytes/ovary) than in other puyen populations, but the egg production increases through individual repetitive spawnings during the protracted spawning period (from October to February). Females attain larger sizes than those of other South American populations (the largest female reaching 115 mm total length), maximizing its potential fecundity. The present paper contributes to the knowledge of the variability of reproductive traits of G. maculatus in relation to diadromic populations, given that the bulk of information in South America refers to landlocked populations.     

Time course of oocyte development in winter flounder Pseudopleuronectes americanus and spawning seasonality for the Gulf of Maine,Georges Bank and southern New England stocks

Winter flounder Pseudopleuronectes americanus were collected at monthly intervals from December 2009 to May 2011, to describe the pattern and seasonality of oocyte development, including: (1) the group‐synchronous transition from primary to secondary oocytes that initiates immediately after spawning, (2) the slow (months) development of vitellogenic oocytes followed by the rapid (weeks) maturation of oocytes, (3) the synchronous nature of mature oocytes ovulating, but the discrete releases of benthic eggs in batches, (4) the protracted (months) degradation of postovulatory follicles and (5) the occurrence of follicular atresia. Although fish were collected across only c. 2° latitudinal range, the spawning season was c. 1 month later in the Gulf of Maine (GOM) than on Georges Bank and in southern New England. This is probably due to lower temperatures in the GOM. These stock‐specific data regarding the time course of oogenesis are of practical value. This information is discussed in relation to measuring and interpreting elements of reproductive potential such as maturation, skipped spawning and fecundity, the response of reproductive traits by this widely distributed species to changing climate and the response by this common, marine‐estuarine species to urbanization, particularly environmental pollutants and dredging.     

Sexual cycle and seasonal changes in the ovary of the red mullet, Mullus surmuletus, from the southern coast of Brittany

The reproductive cycle of the red mullet is described on a macroscopic scale in terms of the GSI, HSI and K , and on a microscopic scale in terms of histological changes in the ovary and changes in the oocyte size frequency distribution. On the southern coast of Brittany the red mullet breeds in May and June. During oogenesis, the previtellogenic period lasts 6 months and the secondary phase of vitellogenesis no more than 3 months. When spawning commences the process of vitellogenesis ceases and up to 20% of the vitellogenic oocytes become atretic. Prior to spawning a single batch of oocytes can be seen to be entering secondary vitellogenesis. During the immediate prespawning and spawning periods the existing vitellogenic oocytes mature but there is no recruitment from the stock of previteilogenic oocytes. This results in a gap or hiatus in the oocyte size frequency distribution between previtellogenic and vitellogenic oocytes within which there are very few resting or maturing oocytes. The red mullet appears to be a determinate spawner, in which egg loss through atresia considerably reduces the potential fecundity.     

Goosefish Lophius americanus fecundity and spawning frequency,with implications for population reproductive potential

To improve knowledge of goosefish Lophius americanus' reproductive biology, females were collected during 2009–2012 from the Mid‐Atlantic Bight shelf region of the U.S. east coast. Batch fecundity increased with total length (L_T), from 229 100 to 2 243 300 mature oocytes per female (L_T range: 55·5–112 cm; n = 54). This estimate of fecundity at L_T is lower than one derived from a sample collected during 1982–1985. Examination of whole oocyte diameters in different months indicated that L. americanus is a serial spawner, releasing more than one egg veil per spawning season, as suspected or observed for other Lophius species. Seasonality of spawning was evident from whole oocytes and gonad histology, and from larval fish surveys spanning the U.S. north‐east shelf, and confirmed a protracted (c. 6 months) spawning period. Peak spawning activity progressed northward from spring to autumn. The population‐level implications of these results were explored by estimating population reproductive potential (P_RP), which considered the value of both current and future per capita reproduction using decade‐specific age structure and fecundity at length. P_RP is now more than 50% lower compared with the historical period (1982–1985), a result of the lower proportions of large females and reduced fecundity across all sizes. Mechanisms that could explain this loss of stock productivity are fishing‐induced size–age truncation or regime shifts in egg production caused by changes in energy density of common forage species.     

Reproductive strategies of a temperate Australian sciaenid (teraglin,Atractoscion atelodus)

Worldwide there have been declines in stocks of exploited sciaenids. Despite a long history of exploitation, there has been no study of the life history characteristics of the fishery-important sciaenid, teraglin, Atractoscion atelodus. This study describes the reproductive characteristics of A. atelodus within the major area of its distribution and fishery, New South Wales (NSW) Australia. Characteristics studied included the size and age at maturity, fecundity, spawning mode and season, and these are compared to congeneric species. Atractoscion atelodus displays year-round batch spawning behaviour with asynchronous oocyte development and indeterminate fecundity. This is unusual for sciaenids, which typically display spring-summer spawning and only over a few months. The length and age at which 50% of the population matures for both males and females is 36 cm fork length (FL) and 1 year, a smaller size compared to other closely related sciaenids. While the species displays resilient reproductive characteristics such as protracted year-round spawning, constant supply of vitellogenic oocytes and relatively small/young age at maturity, there are also characteristics that make it susceptible to over-exploitation. These include highly female skewed sex ratios, as well as their schooling and voracious feeding behaviour leading to the potential for high catch rates.     

The effect of oocytic atresia on fecundity estimates of the rabbit fishSiganus sutor (Pisces: Siganidae) of Kenyan marine inshore waters

In the strongly group-synchronized oocyte development ofSiganus sutor (Valenciennes, 1835) the group of oocytes to be released in the following spawning, is identified. The smallest size of oocyte belonging to this group was identified by the presence of cytoplasmic vacuoles in oocytes in histological sections. These vacuolated oocytes corresponded to oocytes of 150 µm diameter obtained by treatment with Gilson's fixative. The mean number of such oocytes in stage 4 (late developing) ovaries was found to be 638 000. The proportion of these oocytes removed by atresia before spawning was determined on histological sections to be 5%. The corrected estimate of mean fecundity was thus 606 000 oocytes per spawning.