Oocyte Size Distribution Research Articles

Sex ratios, size at sexual maturity, and spawning seasonality of dolphinfish ( Coryphaena hippurus) captured in the Gulf of Tehuantepec, Mexico

Aspects of the reproductive biology of dolphinfish ( Coryphaena hippurus) in the Gulf of Tehuantepec, Mexico, were analysed. A total of 7371 fish were obtained from catches of artisanal fisheries during the period of December 2004–2007. The reproductive activity was assessed using gonad histology, oocyte development, maximum whole oocyte size, maturity, and gonadosomatic index. The sex ratio (males:females) was 1:1, except in April–May (1:1.5, P < 0.05) and November (1:0.5, P < 0.05). The sex ratio at different size classes showed a significant bias towards females at smaller sizes (<75 cm FL), whereas the males were predominant in the larger size classes (>100 cm FL). The estimated size-at-50%-maturity for females was 48.38 ± 0.84 cm, whereas for males it was 50.57 ± 2.16 cm. The batch fecundity for female fish between 49 and 129 cm FL was 45,022–1,930,245 hydrated oocytes per female. The average interval between spawns was 2.0 days. The size distribution of oocytes, with at least two groups of oocytes in the ovaries, suggests that C. hippurus is a multiple spawner with an extended spawning season in the study area. The results suggest a pre-spawning migration and evidence of two main spawning events occurring in May–July and November–January as well as intense utilisation of the coastal zone of the Gulf of Tehuantepec as an area for reproduction, with aggregation behaviour during spawning.

Reproductive patterns of the abyssal asteroid Styracaster elongatus from the N.E. Atlantic Ocean

We analysed the reproductive biology of the asteroid species Styracaster elongatus based on time-series samples from a 5000-m-deep site on the Porcupine Abyssal Plain (N.E. Atlantic). The ratio of males to females, the gonadosomatic index (GI), and pyloric caecum index (PCI) were determined and the results were corroborated by histological examination of the gonads. Fecundity and oocyte-size distribution were determined by histological and image analyses. Styracaster elongatus is a gonochoric asteroid and the ratio of males to females was not significantly different throughout the year. Oogenesis was asynchronous. The previtellogenic oocytes grew to a size of ∼230 μm before undergoing vitellogenesis. Maximum oocyte size was ∼620 μm. The ovary volume was mainly occupied by small previtellogenic oocytes (100–150 μm) at any one time. Mean GI was 6.38±3.30 for females and 9.04±4.1 for males. Mean PCI was 7.44±1.66 for females and 7.66±1.46 for males. Mean fecundity was 16,373±5988 oocites per female. There were no seasonal variations in GI and fecundity. There was evidence of a pyiloric caecum seasonal development for females and males. For S. elongatus there is no direct relationship among seasonal primary production at the surface and production of vitellogenic oocytes. Nevertheless, this species takes advantage of the pulse of phytodetritus to the seabed by increasing the storage of nutrients in the pyloric caecum in order to maintain a constant production of eggs and sperm.

Life-history traits of non-native black bullheadAmeiurus melaswith comments on its invasive potential

Summary Life-history traits of non-native black bullhead Ameiurus melas from an oxbow of the River Vah (near the city of Komarno), located in the middle Danube reaches (Slovakia) were investigated during 2006 and 2007, including samples from the pre-spawning (March-May), spawning (May-June), post- spawning (late June-August) and resting (September) periods. In total, 600 specimens were examined. The sex ratio oscillated close to 1 : 1. Females were found to mature at 98.6-120 mm SL (118-145.1 mm TL, compared to 171-254 mm TL in the native North American populations). Spawning took place in May and June, although the spawning period in 2007 was more protracted. Based on the analyses of annual gonadal cycle and oocyte size distribution, the black bullhead is considered a multiple spawner with asynchronous oocyte development and indeterminate fecundity. Absolute fecundity ranged from 1238 to 4755 (mean 2610), and relative fecundity from 36.2 to 154.3 (mean 56.1) oocytes g )1 . The high flexibility in the life history of the black bullhead as demonstrated by its non-native populations, as well as its extreme tolerance and capability to live in systems with poor water quality, suggests that this species has a high potential to invade new areas and establish viable populations.

Asynchronous and synchronous spawning by smalleye shiner Notropis buccula from the Brazos River, Texas

Abstract – We used a combination of methods to study the reproductive ecology of the imperiled smalleye shiner Notropis buccula Cross in the Brazos River, Texas between April 2003 and March 2005. Patterns in oocyte development, gonadosomatic index and oocyte size distribution indicate that reproduction occurs over a 6‐month period between April and September and that the population spawns asynchronously with individual fish spawning small batches of ova throughout the reproductive season except during periods of elevated streamflow when spawning becomes more intense and is synchronised within the population. This combination of asynchronous spawning and episodic synchronous spawning in the same species challenges the current paradigm of an exclusive association between spawning and periods of elevated streamflow for pelagic, broadcast‐spawning cyprinids in North American Great Plains Rivers. The combination of asynchronous and synchronous spawning that we observed for the smalleye shiner is likely widespread among pelagic, broadcast‐spawning cyprinids and limitations of the methods commonly used to assess reproductive ecology likely contributed to an incomplete understanding of the relationship between spawning and streamflow. An accurate understanding of this relationship is necessary to design and implement appropriate conservation and management strategies for the smalleye shiner and other imperiled broadcast‐spawning cyprinid fishes.

Dinâmica populacional de &lt;em&gt;Characidium lauroi&lt;/em&gt; e &lt;em&gt;C. alipioi&lt;/em&gt; (Teleostei, Crenuchidae) na microbacia do Ribeirão Grande, serra da Mantiqueira Oriental, Estado de São Paulo

In low-order streams, the high and variable water flow rates offer both advantages and disadvantages to the life cycle of fishes. Even closely related species living in similar habitats can show differences in life history patterns. Based on oocyte-size distributions, C. lauroi was classified into the fractional spawning type, and C. alipioi into the total spawning type. The absolute fecundity of C. lauroi ranged from 1,313 to 2,925 oocytes; in C. alipioi the absolute fecundity ranged from 2,213 to 25,550 oocytes. The nonparametric Spearman correlation test showed statistical significance between the gonadosomatic index and fecundity for both species. The growth parameters, natural mortality rate and survival rate for females of C. lauroi were: K = 0.68 yr -1 , L oo = 8.7 cm, t max = 4.4 years, M = 1.62 yr -1 , S = 19.79%, and for males: K = 0.78 yr -1 , L oo = 6.9 cm, t max = 3.8 years, M = 1.89 yr -1 , S = 15.11%. The growth parameters, natural mortality rate and survival rate for females of C. alipioi were: K = 0.90 yr -1 , L oo = 12.2 cm, t max = 3.3 years, M = 1.81 yr -1 , S = 16.37%, and for males: K = 0.76 yr -1 , L oo = 10.1 cm, t max = 3.9 years, M = 1.71 yr -1 , S = 18.10%.

Spatial and temporal dynamics of reproduction and settlement in the Pompeii worm Alvinella pompejana (Polychaeta: Alvinellidae)

The tubicolous polychaete Alvinella pompejana (Desbruyeres & Laubier) inhabits deep- sea hydrothermal vents. To assess its reproductive and recruitment strategies in response to such extreme conditions, populations of A. pompejana were sampled at various spatial scales: among hydrothermal vents within the 13°N/East Pacific Rise vent field and among vent sectors along the southern East Pacific Rise. Additional samples were collected at 1 vent 31 d apart to determine short- term temporal variations. Such a sampling strategy allowed us to conduct an integrated study of both the spatial variation of the reproductive dynamics (i.e. fecundity, oocyte distribution) and the popula- tion structure of this polychaete. Despite a 1:1 sex ratio for each population, a male-biased sex ratio was found at sexual maturity, which could maximise reproductive success in this spermathecae- bearing species. Oocyte size distributions in mature females distinguished 5 maturity stages related to the presence of 1 to 5 distinct oocyte size groups. Coelomic fecundity, which is among the highest known in polychaetes (max. 978 000 oocytes), depends on the maturity stage, but not on the size of the female. The analysis of oocyte distributions strongly highlighted that reproduction is semi- continuous. Mature oocytes are however discretely recruited in the gonoducts from a massive stock of coelomic oogonia and spawned in pulses that may be synchronised between reproductive females. Size-frequency distributions of organisms displayed polymodal structure, suggesting discontinuous recruitment that may be locally affected by the vent dynamics or variations in larval supply. The dis- crepancy between semi-continuous reproduction and a polymodal size-frequency distribution may be explained by: (1) a limited amount of recruits within populations, (2) rapid growth during the early benthic phase, and/or (3) an accumulation of individuals of different ages in the adult cohort. Nearly continuous production of gametes and storage of mature oocytes and/or sperm seem to be a general trend selected in hydrothermal-vent polychaete species.

Multi-year observations on the gametogenic ecology of the Antarctic seastar Odontaster validus

This study reports the first multi-year observations on the reproductive patterns for an Antarctic predator/scavenger, Odontaster validus (Koehler 1912). Seastars were collected monthly from a shallow site (15–20 m depth) near the British Antarctic Survey (BAS) Rothera Research Station (Adelaide Island, 67°34′S 68°08′W) from July 1997 to January 2001. Reproductive condition, oocyte size frequencies and spermatogenesis were examined in at least ten seastars each month using histological and image analysis techniques. Gonad indices (GI) and pyloric caeca indices (PI) were also examined in the same samples. Female and male GIs varied seasonally, in parallel with a reduction in the proportion of large oocytes and mature sperm in the gonad in August to mid-October following winter spawning. Despite there being remarkable consistency in the timing of spawning from year to year, differences in the reproductive condition of individuals were apparent. Patterns in the digestive tissues also varied with season, peaking in December and reaching a minimum in February in two of the three study years. This weaker annual pattern may partly reflect the varied diet of this predator/scavenger species, which is not directly dependant on the timing and magnitude of the annual phytoplankton bloom. Pooled oocyte size distributions and residual analysis suggested that oogenesis progressed over 18–24 months, with the largest of the two size classes (maximum diameter = 183 μm) being spawned annually. This pattern of oocyte growth and spawning was previously reported in the early 1960s for an O. validus population from McMurdo Sound, which lies south of Rothera by 10° latitude. The extremely catholic diet of this predator/scavenger suggests the reproductive patterns of the seastar will be less susceptible to changes in food supply compared to polar suspension feeders or deposit feeders.

Reproductive biology of the deep-sea asteroid Henricia abyssicola from the NE Atlantic Ocean

The reproductive biology of the North Atlantic asteroid Henricia abyssicola is determined in time series samples taken from 1250 to 1900 m depth in the Porcupine Seabight (NE Atlantic). The male-female ratio, gonadosomatic index (GI), pyloric caecum index (PCI), fecundity and oocyte size distribution were determined and the results were corroborated by histological examination of the gonads. This species is a gonochoric asteroid and the male-female ratio did not differ significantly from the equality. Oogenesis was asynchronous. The previtellogenic oocytes grow to a size of ~230 µm before undergoing vitellogenesis. Maximum oocyte size was ~970 µm. The ovary volume was mainly occupied by large vitellogenic oocytes (400–500 µm) at any time. There were no seasonal variations in GI, PCI and fecundity. There were, however, variations in the production of vitellogenic oocytes of H. abyssicola superimposed on the continuous reproduction. We suggest that H. abyssicola makes use of the energy source provided by the deposition of phytodetritus by storing it in the developing oocytes and that it might have the benefit of a facultative planktotrophic larva.

Signs of multiple spawning in Graneledone pacifica (Cephalopoda: Octopodidae)

The examination of five females of the deep-benthic octopus Graneledone pacifica—a large-egged species: mature ovarian egg length &gt;20 mm—showed that their developing oocyte size-distribution was normal in two specimens at an early maturation stage (largest oocyte length=3 mm), bimodal in two specimens at a more advanced stage (largest oocyte length=6 and 8 mm, respectively), three-modal in the farthest advanced stage specimen (largest oocyte length=14 mm). According to the literature, the simultaneous occurrence of oocyte cohorts at different oogenic stages, including a distinct cohort of oocytes at an advanced maturing stage in one specimen, suggests that G. pacifica is a multiple spawner.

Population biology and life strategies of Chlorophthalmus agassizii Bonaparte, 1840 (Pisces: Osteichthyes) in the Mediterranean Sea

The population biology and life strategies of Chlorophthalmus agassizii were studied in the Ionian Sea (eastern–central Mediterranean) using the data collected during the experimental trawl surveys carried out from 1995 to 2000. Depth-related trends of both density and size were found. With depth the former decreased while the latter increased. A typical bigger–deeper phenomenon was detected: young-of-the-year individuals occur on the shelf during autumn–winter months and move towards bathyal bottoms as they grow. The sampled population was made up of several size–age groups. The maximum age of 8 years was identified by means of otolith readings. The Von Bertalanffy growth parameters were estimated from the age–length key (L ∞=189.04±5.401 mm; k=0.24±0.021; t o=−1.20±0.132; φ′=3.94) and modal progression analysis (L ∞=218.33±18.397 mm; k=0.164±0.028; t o=−1.694±0.171; φ′=3.89). Reproduction of this monoecious fish was observed during summer–early autumn. Considering the female portion of the gonad, the size at attainment of 50% maturity was 115 mm TL. The corresponding age is within the third year of life. The simultaneous occurrence of oocytes in different development stages was shown in the ovary. Both the asynchronous ovary and oocyte size distribution indicate that C. agassizii spawns more than once during a reproductive season (batch spawner). Functional fecundity (on average 3,018 hydrated oocytes) was between 37 and 69% of the absolute fecundity and increased significantly with the individual size. Since adult specimens are mostly distributed on the slope, eggs and larvae develop in epipelagic waters and migrate in-shore where juvenile forms recruit on the shelf. Juveniles migrate ontogenetically towards deeper bottoms and after 2–3 years start to reproduce annually within a life span greater than 10 years.

Effects of different long-day photoperiods on somatic growth and gonadal development in Nile tilapia ( Oreochromis niloticus L.)

Long-day photoperiods are considered as an effective managerial tool in manipulating somatic growth and reproduction in a number of fish species. Effects of three different artificial long-day photoperiods on somatic growth and gonadal development of Nile tilapia ( Oreochromis niloticus L.) were investigated in this study. Swim-up fry with a mean initial weight of 0.06 g were exposed to 24L:0D, 20L:4D and 18L:6D artificial photoperiods and ambient light regime (control) for 24 weeks at 27.0 ± 1 °C. The effect of photoperiodic manipulation was only detectable and statistically meaningful during fingerling stage. Long-day photoperiods resulted in significantly higher mean final weights and specific growth rates (SGR) than natural light regime. The highest mean final weight (24.94 ± 0.45 g) and SGR (3.46 ± 0.03% day − 1 ) were obtained under 24L:0D photoperiod. Mean female gonadosomatic index (GSI) and mean oocyte size were significantly lower in fish maintained under continuous light regime (24L:0D) than those of 20L:4D, 18L:6D treatments and control. The highest gonadosomatic indices were recorded in control female and males. Mean oocyte diameter in fish exposed to continuous light was measured as 1.05 ± 0.06 mm with the bulk of the oocytes (60.0%) in pre-vitellogenic stage (≤ 1.20 mm). On the contrary, oocyte size and size distribution of oocytes in 20L:4D, 18L:6D photoperiod groups and control were indicating a more advanced oocyte development stage, i.e. vitellogenic (1.2–1.8 mm) and post-vitellogenic stages (> 2.1–2.4 mm). Basically, results obtained support the idea that continuous artificial lighting may be influential on enhancing somatic growth and delaying gonadal development in Nile tilapia during fingerling stage.

Long-term changes in reproductive patterns of the holothurian Oneirophanta mutabilis from the Porcupine Abyssal Plain

Time-series studies (1989–2002) in the NE Atlantic have shown large-scale changes in the composition and structure of the benthic community on the Porcupine Abyssal Plain. Radical changes in the abundance of some species in 1996 led to a significant shift in the way in which organic matter was reprocessed at the seabed. This article examines the reproductive processes of the holothurian Oneirophanta mutabilis collected during the time series. The reproductive biology of O. mutabilis is reviewed. No males were evident in any of the samples. The sex ratio (females: ‘no gender’) was biased significantly towards no-gender individuals. The maximum egg size was 650 μm and there was no evidence of synchrony in reproduction. Significant changes in the oocyte-size distribution and the fecundity of O. mutabilis were noted through time, coinciding with the time of greatest faunal change in the benthic community. There was an increase in the proportion of previtellogenic oocytes and a decrease in the proportion of mature vitellogenic oocytes in 1997 and 1998, in parallel with a significant decrease in fecundity of the post-1996 samples. Samples from 2002 showed a reversal in the reproductive trends, with an increase in the proportion of mature vitellogenic oocytes and fecundity. The results are discussed in relation to large changes in abundance of the epibenthos on the Porcupine Abyssal Plain. It is suggested that the superabundance of certain megafaunal species on the abyssal seafloor affected the availability of trophic resources for O. mutabilis, leading to the changes in its reproductive effort.

Maturation and diel reproductive periodicity of round scad (Carangidae: Decapterus punctatus )

The diel reproductive periodicity of Carangidae is poorly known but appears to be highly variable between species. Some species spawn during the day, others are believed to spawn at night, and it is demonstrated here that round scad, Decapterus punctatus, spawn at dusk. We collected D. punctatus in the eastern Gulf of Mexico during three April cruises (1995, 1996, and 1997). Based on histological criteria, size at 50% maturity was 113 mm fork length (FL) for males and 128 mm FL for females. The gonad-somatic index (GSI) of mature males was significantly different between hours and appeared to show diel periodicity. Diel periodicity was also observed in changes in female GSIs, whole oocyte diameters, and ovarian histology. The average GSI of mature females fluctuated two-fold between day and night, and the size distribution of whole oocytes in some fish was bimodal (at 0.3–0.4 and 0.7–0.8 mm diameter) at dusk rather than unimodal during most of the diel cycle. Histological preparations revealed that these rapid changes in ovarian GSIs and oocyte size distributions were the result of final oocyte maturation. Germinal vesicle migration was observed from 0900 to 1400 hours eastern standard time (EST), germinal vesicle breakdown was evident as early as 1100 hours EST, and ovulation occurred as early as 1800 hours EST. Spawning frequency (approximately every 5 days) was similar whether calculated from the proportion of females with hydrated oocytes during the afternoon or from the proportion of females with postovulatory follicles during the morning. Batch fecundity correlated with fish size and ranged from 5,500 to 34,700 hydrated eggs per individual. These findings do not support published hypotheses that young-of-the-year D. punctatus reproduce before their first winter or that D. punctatus reproductive output is bimodal within a year.

Size distribution and meiotic competence of oocytes obtained from bitch ovaries at various stages of the oestrous cycle.

The present study was conducted to examine the effects of the stage of the oestrous cycle on the meiotic competence of canine oocytes and also to investigate the relationship between the stage of the oestrous cycle and the relative size distribution of oocytes obtained from bitches at three stages of the cycle (anoestrus, follicular phase and dioestrus). Only healthy-looking cumulus-oocyte complexes were used for in vitro maturation and these were divided into three groups based on diameter (< 110, 110 to < 120 and > or = 120 microm). The mean diameter of oocytes from ovaries at anoestrus, the follicular phase and dioestrus was 103.6, 119.2 and 107.7 microm, respectively. The percentage of large oocytes (> or = 120 microm) collected at the follicular phase was higher (P<0.01) than that collected at dioestrus and the percentage of oocytes > or = 120 microm collected from ovaries at dioestrus was higher (P<0.01) than that collected at anoestrus. After culture for 72 h, significantly more oocytes reached metaphase II (MII) in the follicular phase than in the other stages (P<0.01), and more oocytes reached MII in dioestrus than in anoestrus (P<0.05). In the > or = 120 microm group, the frequency of oocytes that resumed meiosis in the follicular phase was higher (P<0.05) than in the other stages. However, in the smaller diameter (< 120 microm) groups, there were no significant differences between ovaries at different stages of the oestrous cycle with respect to the proportion of oocytes reaching each stage of meiosis. Thus, the oestrous cycle stage influences maturation frequency. Moreover, oocytes demonstrated a size-related ability to undergo meiotic maturation, irrespective of the stage of the oestrous cycle. These results suggest that the effects of the stage of the oestrous cycle may result from differences in the distribution of large oocytes.

Fecundity and spawning mode of three introduced fish species in Lake Banyoles (Catalunya, Spain) in comparison with other localities

Analysis was conducted during 1991 into the fecundity and oocyte size distribution of pumpkinseed, roach and rudd in Lake Banyoles. We found that individual fecundities of these species in Lake Banyoles were lower in comparison with other localities. In roach, there was a moderately significant negative relationship between latitude and egg number. The temporal pattern of the pumpkinseed's oocyte size distribution suggests that it is a multispawner fish that spawns several batches of eggs from mid-May to mid-August. In contrast, roach and rudd seem to be monospawners fish that release only one batch of eggs before mid-May. The monospawning behaviour of rudd in Lake Banyoles is in contrast to the evidence from other waters. Variations in fecundity and spawning mode are discussed on the basis that they are due mainly to differences in local conditions.

Effects of temperature on oocyte growth in the Mediterranean terebellid Eupolymnia nuebulosa (Annelida: Polychaeta)

Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polychaete that builds its tubes on the coastal shelf in areas with mixed soft and hard bottoms. From a long-term survey in the Bay of Banyuls, France (NW Mediterranean), we found an advancement of the timing of the spawning period coincident with a delayed breakdown of the thermocline. We postulate that persistent high temperatures can influence gamete development by stimulating oocyte growth, resulting in earlier spawning. During 1992 and 1993, we used a between-individuals experimental approach to assess the possible effect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte population (i.e. oocyte net growth); (2) identification of differences in oocyte growth-rate among females; (3) comparison of non-significantly different size-distributions of the growing oocyte fraction (net oocyte size-distributions) at the beginning of the experiments with those at the end. No effect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a significant response by the population to prolonged high temperature does not imply a lack of individual response. We propose a model of oocyte-growth dynamics based on temperature that incorporates previous observations of extended oogenesis and oocyte growth during periods of both increasing and decreasing temperature and on the scattered pattern of oocyte size-distributions at the onset of spawning.

Reproductive biology of dolphin-fish ( Coryphaena hippurus L.) off the island of Majorca (western Mediterranean)

The reproductive aspects of Coryphaena hippurus were studied in 410 specimens collected by long line (60–120 cm fork length) and surrounding net (14.4–66 cm fork length) in Majorcan waters (western Mediterranean) during the 1990 and 1991 fishing seasons. Sexual dimorphism was observed, males from 50 cm fork length developing a vertical forehead. The sex ratio was 1:1. Fish smaller than 25 cm fork length were predominantly females, while males were more abundant over 115 cm fork length. The composition of each sex during the study period was around 50% except in December, when females were clearly predominant. A high proportion of fishes caught by long line were mature and showed gonadosomatic values higher than those obtained from surrounding net catches, in which there were only immature fish. Nevertheless, hepatosomatic index and condition factor did not show any specific trend related to the spawning condition. The size at which the population attain 50% maturity was 54.5 cm fork length in females, and 61.8 cm fork length in males. In 14 pre-spawning females, the relative fecundity ranged from 71 to 197 eggs g −1, with a mean value of 120 ± 31.3 eggs g −1. The size distribution of oocytes, with at least two groups of oocytes in the ovaries, suggests that C. hippurus is a multiple spawner, with an extended spawning season in the study area.

Observations on the reproductive biology of female Hypostomus luetkeni Lacèpéde 1803

Abstract— Seasonal observations in the gonadosomatic index and development stages of female ovaries showed that Hypostomus luetkeni has an extended spawning period lasting from September to February. Histological examinations and analysis of oocyte size distributions indicated a fractional spawning. Fecundity was determined in ripe ovaries and indicated that H. luetkeni, as most other Loricariidae, spawn a small number (446‐936 eggs‐ind−1) of large eggs (5.2 mm).

Plasma steriod hormone concentrations in relation to reproductive cycle of the sweep Scorpis lineolatus (Kyphosidae) caught from the wild

Changes in gonadosomatic index (GSI), hepatosomatic index (HSI), oocyte development and plasma levels of steroid hormones were studied during the reproductive cycle of the sweep Scorpis lineolatus. GSI values for both sexes were maximal in March and April. During this period the size distribution of oocytes showed a predominance of advanced stages of vitellogenesis, whereas males were completing spermatogenesis. However, staging data suggest that spawning may not begin until April. HSI was maximal 2 months prior to the beginning of gametogenesis in both sexes. Plasma concentrations of oestradiol-17β in females increased rapidly from February, reached a peak (2.3 ng mL-1) in association with the end of vitellogenesis in March, and returned to low concentrations in May and June. Plasma concentrations of 17α,20α-dihydroxy-4-pregnen-3-one (17,20βP) also peaked in March in females, but 17,20βP was generally not detectable in males. Plasma testosterone concentration peaked along with other steroids in March in females but showed no significant change in males. Plasma ll-ketotestosterone (1 1KT) concentration was maximal in males before spawning (February), but was not elevated during the spawning period itself. Changes in oestradiol-17β and testosterone in association with vitellogenensis in females are consistent with those reported for other teleosts, whereas changes in 17,20βP, testosterone and 11-ketotestosterone in males are different from those previously reported.

Size distribution and meiotic competence of bovine primary oocytes from two locations in the ovary

Size distribution and meiotic competence of bovine primary oocytes from two locations in the ovary