Batch fecundity and spawning frequency of invasive Hemiculter leucisculus (Basilewsky, 1855) in Erhai Lake,China

Hemiculter leucisculus are multiple spawners with indeterminate fecundity, although previous fecundity estimates have assumed a determinate spawning pattern. Batch fecundity and spawning frequency of H. leucisculus were studied in Erhai Lake, China, in which the fish, as an exotic species, has become a successful colonizer. Spawning frequency was 16.05 %, as determined from the percent of females with postovulatory follicles 12 to 36 h old during the peak reproductive period (from May 27 to August 8). The average interval between spawning was 6.2 days and there were more than 16 total spawning batches during the peak reproductive period. The average batch fecundity (mean ± SD) was 11,934?±?5,921 hydrated oocytes in 40 females (standard length or SL: 9.1–14.4 cm), while relative batch fecundity was 560?±?137 eggs g^?1 wet weight. The total potential annual fecundity was approximately 190,944 oocytes over the whole spawning season and was much higher than the estimated standing stock (31,585 oocytes) of yolked oocytes (36 females, SL: 9.5–16.2 cm) at the beginning of the spawning season in April 2010. This high annual fecundity is likely to have contributed to successful invasion of Erhai Lake by H. leucisculus.     

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Down‐regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d . total length of the sampled fish was 32·7 ± 3·1 cm and mean ± s.d . age was 6·2 ± 1·5 years. Measurements of atresia were performed using the ‘profile method’ with the intensity of atresia adjusted according to the ‘dissector method’ (10·6% adjustment; coefficient of determination was 0·675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down‐regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.     

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.     

RNA synthesis in the ovary and oocytes of the starfish

Qualitative studies on the in vitro uptake and incorporation of tritiated uridine into RNA of the somatic and germinal elements of the starfish ovary were carried out prior to and during hormone-induced oocyte maturation and spawning.Autoradiography of nonhormone-treated ovaries indicated that the outer ovarian wall contained the highest concentration of label, with lesser amounts in the follicle cells and least in the oocytes. Oocytes and follicle cells localized at the periphery of the ovary were labeled first, and both cells became progressively labeled throughout the ovary with time; the label first appeared localized in the nucleolus of the oocyte.Sucrose gradient analysis of the separated cellular components of prelabeled hormone-treated ovaries indicated that RNA synthesis occurred in all segments of the ovary and that the spawned oocyte fraction was the least active. Synthesis of ribosomal RNA was detectable after a lag period of approximately 4 hr. Oocytes incubated in ³H-uridine during and subsequent to 1-methyladenine-induced spawning and maturation synthesized 15–19 S and low molecular weight RNA but not ribosomal RNA. Synthesis of the 15–19 S RNA was inhibited with ethidium bromide and to a limited extent by actinomycin D. Isolated mitochondrial fractions contained most of the labeled 15–19 S RNA. These data suggest the mitochondrial origin of most, if not all, of this intermediate-weight RNA. On the basis of these studies, it appears that starfish oocytes and follicle cells are metabolically active at the transitional period from growth to maturational stages in oocytes. Synthesis of RNA furthermore apparently continues in the cytoplasm subsequent to germinal vesicle breakdown and spawning.     

Pattern of sea bass oocyte development after ovarian stimulation by LHRHa

The cyclic pattern of oocyte development in the sea bass, Dicentrarchus labrax L., was studied after induction of spawning by two injections, 24 h apart, of a luteinizing hormone releasing-hormone analog (LHRHa) administered at the end of vitellogenesis. The first difference in the developmental stage of the ovary and in the size-frequency distribution of oocytes between the LHRHa treated group and the control group, was detected 32 h after the first injection, the LHRHa group showing a higher proportion of the 900 μm diameter oocyte class (maturing oocytes) ( P <0.01). At 48 h LHRHa-treated females showed an increase in the 1000 and 1100 μm classes (maturing oocyte and ovulated eggs) ( P <0.01) and at 72 h these females exhibited a bimodal pattern, reaching the highest proportions in the 1100 (27.4%) and the 600 (14.7%) μm classes (ovulated eggs and advanced vitellogenic oocytes, respectively). Bimodal distributions were present in 80% of the LHRHa-treated females. Once oocyte final maturation was triggered by LHRHa the time needed for ovulation was about 48 h and the interval between consecutive ovulations and spawnings seemed to be 48–72 h.     

In vitro Inhibition of Oocyte and Follicular Maturation and Spawning in Starfish (Asterias forbesi) by 2-4-Dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of ³H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

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.     

The ovarian maturation cycle of the Norway lobster Nephrops norvegicus (Linnaeus, 1758) (Crustacea,Decapoda) from the western Mediterranean Sea

Summary

The Norway lobster Nephrops norvegicus lives in the continental margins of the western Mediterranean Sea at depths between 100 and 600 m. It constitutes an important fisheries resource and presents a seasonal reproductive pattern. Female Norway lobsters were obtained each month from a vessel fishing off Barcelona. One hundred females caught in June 2002 were kept in the laboratory. After spawning, ovarian samples were taken every 30 days with the objective of monitoring the first steps in ovarian maturation. The gonado-somatic index (GSI) remained low over the 6 months during which the females carried their eggs, plus for a further 2–3 months. However, this study suggests that ovarian maturation is a continuous process with two different phases, taking at least 6–8 months during which the female carries its eggs. There is an increase in oocyte numbers; the germinal zone produces oogonia; and the oocytes that develop migrate to the periphery, pushing the post-ovulatory follicles to the wall of the ovary and reinforcing it for subsequent spawning. Besides this increase in the number of oocytes, vitellogenesis begins 2–3 months after the eggs hatch. Oocytes then grow and the ovaries gain weight and change from a cream color to a blackish-green. When the GSI reached 10, spawning occurred and, from then on, the ovary is mainly composed of post-ovulatory follicles.     

Site of production of meiosis-inducing substance in ovary of starfish

The site of production of meiosis-inducing substance (MIS), produced in the ovary under the influence of gonad-stimulating substance (GSS) taken from radial nerves, was studied with the starfish, Asterina pectinifera. The rate of oocyte maturation observed in isolated oocytes with follicles kept in sea water containing GSS (100 μg/ml) was generally low when a small number of eggs per unit quantity of sea water was used. However, with increased number of oocytes per milliliter of GSS-sea water, the maturation rate increased up to 100% (10⁴ eggs/ml). The supernatant of such an incubation mixture of oocytes and GSS contained an appreciable amount of MIS. When a large number of oocytes (10⁴/ml) was used, the rate of oocyte maturation increased with the rise in concentration of GSS. Isolated follicles were found to produce MIS when incubated in sea water containing GSS, suggesting that the site of production of MIS is the follicle cells. The physiological role of the follicle cells surrounding the full grown oocytes seems to be to produce MIS just before spawning under the influence of GSS.     

In vitro inhibition of oocyte and follicular maturation and spawning in starfish (Asterias forbesi) by 2-4-dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of 3H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.     

Cyto-histological examination of post-vitellogenesis and final oocyte maturation in captive-reared striped bass

The ovarian development of captive-reared, striped bass Morone saxatilis was examined during a 10-week period encompassing the spawning season. Vitellogenic oocytes in March had a mean diameter of 838 ± 18 μm and did not grow significantly thereafter. Except from one non-hormone-treated fish, all females failed to undergo final oocyte maturation (FOM) and their ovaries became atretic with the onset of high spring temperatures. A clearing fixative was found useful in identifying early stages of atresia, evident by the absence of the germinal vesicle (GV). Final oocyte maturation of fish treated with gonadotropin-releasing hormone agonist (GnRHa) consisted of two phases. Early FOM lasted from 1 to 3 weeks, and was associated with lipid-droplet coalescence, and displacement of the GV and yolk globules to the peripheral cytoplasm. Late FOM lasted <24h, and consisted of yolk-globule coalescence and GV breakdown (GVBD). Ovulated eggs had completely coalesced lipid and yolk masses, with cortical alveoli lined against the cell wall. Both phases of FOM were associated with significant increases in oocyte diameter. Striped bass oocytes showed important morphological differences compared to oocytes of other members of the Moronidae family, in terms of percentage lipid content, chorion thickness and degree of hydration after ovulation.     

Gonadal maturation,fecundity, spawning,and timing of reproduction in the mud snail,Cerithidea cingulata,a pest in milkfish ponds in the Philippines

Summary

Gonadal maturation, spawning, fecundity and timing of reproduction of the snail Cerithidea cingulata in a brackish water pond in Molo, Iloilo, Philippines, are described. Snails 4–41 mm in shell length were sampled monthly from May 1997 to May 1998; 25% were <25 mm, 67% were 20–30 mm, and 8% were >30 mm. The sexes are separate and could first be distinguished at 15 mm. Males are aphallic, have narrower shells than females of the same length, and have bright yellow-orange testes overlying the digestive gland deep inside the shell. Females have more robust shells, an ovipositor at the right side of the foot, and yellow-green ovaries overlying the digestive gland. The sex ratio was one male to two females in the pond population studied. Gonadal maturation was monitored by means of gonadosomatic index (GSI, gonad weight as a percent of visceral weight); maturation stages were based on the gonad appearance (immature, developing, mature) and histology (immature, developing, mature, redeveloping). GSI increased with snail size, and reached 16% in a 33-mm female. The smallest mature males and females were 18–19 mm, and most snails >20 mm were mature, spawning, or redeveloping. Histological sections showed all stages of gametogenesis in mature male snails. The oocyte size-frequency distributions in mature females showed mostly mature oocytes and secondary oocytes, but also oogonia and primary oocytes. GSI and the frequency of snails at different maturation stages varied over the year. Both GSI and the frequency of mature snails were highest during the summer months, April to August. Nevertheless, mature snails occurred throughout the whole year, as did mating and egg-laying. Fecundity (= number of oocytes >70 pμ) increased with size in mature females 2041 mm; an average 25-mm female produced about 1,500 oocytes and larger females produced a maximum of about 2,500 oocytes. Eggs strings laid on the pond bottom were 45–75 mm long; an average 64-mm string contained 2,000 eggs 210+20 pm in diameter. The density of eggs strings was highest (80–120/m²) during March-September. Eggs hatched after 6–7 d into planktonic veligers, which in turn settle on the pond bottom 11–12 d later as juveniles. Juveniles 2–6-mm long were most abundant in the pond during August-October.     

The equine oocyte: Factors affecting meiotic and developmental competence

There is currently much interest in assisted reproduction techniques in the horse, however, many aspects of oocyte maturation, fertilization, and embryo development in the horse differ from those in other species. Because of the close attachment of the equine oocyte to the follicle wall, scraping of the follicle is the most effective method for oocyte recovery. A notable feature of equine oocytes is that those with expanded cumuli (Ex oocytes), which originate from atretic follicles, have higher meiotic competence (ability to mature to metaphase II in vitro) than do oocytes with compact cumuli (Cp oocytes). Cp oocytes originate in viable follicles but are largely juvenile. Recovery and culture of equine oocytes immediately after slaughter yields a higher maturation rate than that obtained from oocytes after ovary storage; this is related to damage to chromatin in Cp oocytes during storage. In contrast, developmental competence (rate of blastocyst development in vitro) is higher in oocytes recovered from the ovary after a delay. The optimum duration of maturation varies based on cumulus morphology and time of recovery from the ovary, but there is no difference in developmental competence between Ex and Cp oocytes. Because standard in vitro fertilization is not repeatable in the horse, oocyte transfer (surgical transfer of oocytes to the oviducts of inseminated mares) has been developed to allow fertilization of isolated oocytes. Fertilization in vitro may be achieved using intracytoplasmic sperm injection; culture of injected oocytes in a medium with high glucose can yield over 30% blastocyst development. Mol. Reprod. Dev. 77: 651–661, 2010. © 2010 Wiley‐Liss, Inc.     

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.     

Pigmented Follicle Cells and the Maturation of Oocytes in the Sand Dollar, Dendraster excentricus

Early in the spawning season female D. excentricus can be induced to spawn oocytes in the late stages of oogenesis. Observations with light microscopy indicate that pigment cells migrate in the jelly coat away from the surface of oocytes coincident with the final growth of the oocyte and its maturation. The pigment cells undergo a series of changes in shape and the oocyte elaborates arrays of long microvilli as the cells elevate from the surface of the oocyte. Transmission electron microscopy (TEM) observations of oocytes fixed within the ovary indicate that features of the sequence observed in the spawned oocytes normally take place within the ovary, prior to spawning. Extracts of the pigment cells induce a low level of germinal vesicle breakdown in asteroid oocytes. It is proposed that these cells are homologous to the follicle cells of other echinoderms and are involved in stimulating the maturation of oocytes.     

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.     

Oocyte size and structure in relation to blood plasma steroid hormones in individually monitored, spawning Atlantic cod

A series of seasonal blood and ovarian tissue samples were taken from five female Atlantic cod Gadus morhua at different times between various batches of eggs and subsequently examined for oocyte size, plasma steroid hormones and ultrastructure of the cortex oocyte cytoplasm and follicle layer. This detailed protocol demonstrated that the spawning cod ovary is vitellogenically very active. Individual oocytes were able to develop at different rates, and at least two cohorts of oocytes with a different developmental status were present simultaneously. The concentration of estradiol-17β varied between batches and decreased over the season. The levels of 17,20β-P and 11-deoxycortisol were generally low. Oocytes of an advanced developing cohort showed numerous coated vesicles and closely apposed oocytic and follicular microvilli located in the chorionic pores. The number of oocytic microvilli was estimated at about 1–8 million cell⁻¹, which increased the oocyte surface area by a factor of 12. Furthermore, the oocytic microvilli were found to stretch during final maturation. This stage-specific mobility of microvilli is discussed in relation to further incorporation of yolk and the relevant actin-based cytoskeleton observed for other classes of animals.     

Reproductive ecology of the glacier lanternfish Benthosema glaciale

Myctophids play a key role in the transfer of energy in pelagic food webs, linking zooplankton to higher trophic levels. Data are presented, for the first time for the glacier lanternfish (Benthosema glaciale), on maturity ogives, size-at-maturity and reproductive strategy in terms of ovarian organization and fecundity type in two contrasting environments: North Atlantic and Mediterranean. We analysed 292 females collected in Flemish Cap during early summer 2009 and 2011 and off the Balearic Islands during late autumn 2009 and early summer 2010. The spawning season differed between areas. Size at 50% maturity in Flemish Cap was 47.6 and 49.1 mm in 2009 and 2011, respectively, but significantly smaller, 24.5 mm, in the Balearic sea. B. glaciale is a batch spawner with asynchronous ovarian development and indeterminate fecundity. Batch fecundity showed significant relationships with length and weight, although average relative batch fecundity was low (1031 ± 396 oocytes/gram). We compared two staining techniques: Hematoxylin–eosin and PAS–hematoxylin–metanil yellow with the latter being more useful to detect mature females and spawning indicators in regressing and regenerating females. Our results contribute to a better understanding of the reproductive potential and ecological role of this species, the most abundant myctophid in the northern Atlantic.     

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.