Spawning pattern and type of fecundity in relation to ovarian allometry in the round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Spawning pattern (assessed by seasonal changes in ovarian developmental stages) and type of fecundity (assessed by analysis of oocyte-size frequency distributions) of the round herring Etrumeus teres were studied in relation to ovarian growth and seasonal changes in the gonadosomatic (GSI), hepatosomatic (HSI) and liposomatic (LSI) index as well as the somatic condition of spawners (CS) in a spawning ground of southern Japan. Except for summer, mature and recently spawned ovaries occurred all year round. Oogonia and primary oocytes were present in all ovaries, and cortical alveoli stage (CA) oocytes occurred in all mature, hydrated and partially spent (PS) females (PS: females containing post-ovulatory follicles). Before hydration, a clutch of larger yolked oocytes, undergoing synchronous growth (range 0.7–1.1 mm), was present in mature ovaries which was completely separated from a more heterogeneous clutch of oogonia, primary and secondary oocytes (<0.150 mm) and oocytes in the CA stage (range 0.15–0.60 mm). As vitellogenesis progressed, the yolked clutch increased in size but the CA oocytes remained arrested. The latter entered into the secondary growth phase when hydration started in the advanced batch. Ovarian growth was isometric in all developmental stages, validating the use of GSI, which showed a consistent monthly evolution among years. Spawning stopped in summer (July and August) and peaked in winter and spring. HSI correlated positively with GSI on both a monthly mean basis (r = 0.76) and individual fish basis (liver weight explained 67–83% of the variability in ovary weight when females were grouped into 1-unit GSI intervals) suggesting a significant role of liver in vitellogenesis. LSI and CS also showed marked seasonal changes peaking from summer to middle autumn. Overall results suggest that E. teres is a multiple spawner with a group-synchronous ovarian development and indeterminate annual fecundity, with the three processes linked to an isometric growth of the ovary. We propose that such a reproductive pattern is an adaptation to produce batches of large pelagic eggs through a protracted spawning season.     

Ovarian allometry and the use of the gonosomatic index: a case study in the Mediterranean sardine,<Emphasis Type="Italic"> Sardina pilchardus</Emphasis>

The gonosomatic or gonadosomatic index [GSI=(ovary weight/fish weight)×100] has been widely used in fisheries science and experimental reproductive studies as a simple, low-cost measure of reproductive condition. However, its properties have not been fully evaluated, and several pitfalls, such as size-dependence and changes in ovarian allometry, may invalidate its use. In the present study, we examined ovarian allometry and the appropriateness of GSI for assessing ovarian activity in the Mediterranean sardine Sardina pilchardus. The analysis was based on a large sample of histologically scored females collected over an annual cycle in the eastern Mediterranean (Aegean and Ionian Seas). First, we examined GSI dependence on fish size by comparing ovary weight–on–fish weight relationships in different stages of oocyte development. The effects of recent spawning (incidence of postovulatory follicles) and intensity of follicular atresia were also addressed. In a subsequent step of the analysis, we applied generalized linear models (GLMs) to analyze the relationship between GSI and histological stage, taking into account the parallel effects of additional factors related to geographical region, month of capture, fish length and energetic reserves (fat stage, hepatosomatic index—HSI). Ovarian growth was isometric in all stages of oocyte development and states of atresia, but altered to positive allometric at the stage of oocyte hydration. Oocyte growth and intensity of atresia significantly affected GSI. Fish length, geographical region, month of capture, fat stage and HSI did not substantially affect GSI, further strengthening the appropriateness of the index for the Mediterranean sardine. Finally, we provide first evidence, based mainly on available (but yet limited) published information for other fish species, that: (1) the pattern of ovarian allometry may not be altered by fecundity variations and (2) the pattern of ovarian allometry may reflect the pattern of oocyte growth (i.e. isometric vs. allometric ovarian growth could reflect group-synchronous vs. -asynchronous oocyte development). Alternatively, the pattern of ovarian allometry could reflect the presence or absence of size dependency in the relative fecundity (eggs per gram of body weight) and/or egg size. The isometric ovarian growth in the Mediterranean sardine could be attributed to the lack of such size-dependent effects.Communicated by O. Kinne, Oldendorf/Luhe     

First ovarian maturity and recovery response in common carp, Cyprinus carpio after exposure to carbofuran

The present study embodies the observations on duration (45, 75 and 105 days) dependent effects of toxicologically low concentration (16 ppm) of a carbamate pesticide, carbofuran, on first ovarian maturity with correlative recovery response by withdrawal of treatment for 30 days in virgin yearlings of common carp, Cyprinus carpio var. Communis. In control fish histological organization of ovary and changes in gonado-somatic index (GSI) revealed the initiation of oocyte differentiation and development at the commencement of experiment in December-January and peak of maturation with fully grown yolky oocytes was attained by the time of termination of experiment in the end of March. In carbofuran exposed groups ovaries exhibited retardation of development and growth evident by significantly decreased GSI and predominace of immature oocytes passing through nuclear-cytoplasmic degeneration of variable magnitude. Severity of degenerative changes was more pronounced with prolonged duration. In recovery group ovaries had experienced regeneration as clued by the presence of oocytes of differential stages including vitellogenic and fully grown oocytes. In liver histopathological changes coupled with significant decrease in hepato-somatic index (HSI) attributed hepatic inactivation in all exposure groups whereas in recovery group an increase in HSI value with marked sign of hepatic reactivation was evidenced. No significant change in values of condition (CF) and somatic condition (SCF) factors substantiated the over all normal health of fish. Lipid and water content of ovary, liver and muscle registered the significant decrease at 105th day of exposure with concomitant augmented value for recovery group. These observations suggest that the commercial formulation of carbofuran, even at this toxicologically low concentration, is equally capable of affecting the first ovarian maturity with associated physiological implications but with reversibility in toxicity by withdrawal of pesticide exposure attributing regeneration in affected organs in due course time.     

Effect of cortisol on female freshwater fish Notopterus notopterus

In the present study, effect of cortisol on the ovary of the freshwater fish Notopterus notopterus was studied during four phases of the reproductive cycle. The hormone was injected 60microg/fish for ten days. Cortisol in fish is known to increase the metabolic activity. After the hormone treatment the ovarian somatic index and the hepatosomatic index increases during non breeding phase. The young oocytes transferred into vitellogenic oocytes in all the phases after cortisol treatment. The cortisol induced increased ovarian activity may be due to increase in the metabolic activity through the involvement of hepatic cells specially during non-breeding period providing support for energy production for reproductive activity in the freshwater fish N. notopterus.     

Oogenesis and spawn-formation in the pigmy lion fish Dendrochirus brachypterus (Pteroidae)

Dendrochirus brachypterus possesses a special type of ovary in which the germinative epithelium surrounds a spongy stroma hanging in the lumen. The inner side of the ovarian wall is covered by a special type of epithelium that produces a gelatinous envelope around the gametes (spawn) during reproduction. In general, oogenesis in the lion fish resembles that of other teleosts, the characteristic difference being in the formation of ovigerous peduncles-protrusions of the spongy stroma, each of which bears a single oocyte. During oogenesis the oocytes rise above the germinal epithelium, enveloped in their follicular epithelia. The larger the oocyte the greater the length of its peduncles and the further its position from the germinal layer (Fig. 3). During this phase of development, a marked multiplication of yolk granules occurs; they increase their diameter and finally homogenize at ovulation. Under favorable thermal conditions, oogenesis continues all year round. The peduncular growth of oocytes enables the growing egg cells to move away from the egg-producing surface, thus making space available for the ovary to produce more eggs. This ability should have a survival value for these fish if we take into consideration that the most vulnerable stage in their life history is that of planktonic larvae (Fishelson, 1975).     

Ovary structure and oogenesis in Cirratulus cirratus (Polychaeta: Cirratulidae)

Oogenesis in polychaetes has, in most species, two main phases: a coelomic phase during which vitellogenesis occurs, and an ovarian phase. Details of the latter are known in very few species. Efficient reproduction requires coordination between these two phases of oocyte differentiation. The ovaries of Cirratulus cirratus (O. F. Müller) occur 2/segment throughout the fertile region of the body; 5 main stages of oocyte differentiation can be recognised on them: stem cells, oogonia, premeiotic oocytes, early oocytes and terminal oocytes. A quantitative study of the composition of the ovary throughout the reproductive cycle shows that the ovary size is approximately constant, but that the percentage of cells in the terminal oocyte stage is reduced to zero prior to spawning. This stage in oocyte differentiation is therefore a critical one, at which oogenesis may be arrested. The ovary alternates between a proliferative phase when the terminal oocytes are present, and a non-proliferative phase when they are absent. The overall rate of germ cell production for each ovary is low, less than 1 cell/ovary/day, and the, ovary tissue turnover time is greater than 2 years. A qualitative model describing the production of oocytes is presented, and the implications of the low rate of germ cell production are discussed. A low rate of germ cell proliferation, as in Cirratulus cirratus, implies that the rate of oocyte output into the coelom will be controlled by factors influencing the later stages of ovarian oocyte differentiation.     

Ovary development at the onset of gametogenesis is genetically determined and correlated with reproductive traits at maturity in shrimp <Emphasis Type="Italic">Litopenaeus (Penaeus) vannamei</Emphasis>

Besides some mammals and a few model organisms, the presence of genetic variation in ovary or gonad development at ages before that of reproduction has not been established for marine oviparous species nor has the correlation with reproductive traits at maturity. In this investigation, ovary development was evaluated for genetic variability in a full-sib family structured population of subadult shrimp. The numbers of each oocyte type that were present were counted, measured, and used to evaluate the following traits: total oocyte number, mean oocytes diameter, and ovary maturity (OM). The total ovary area was also measured for each female. Genetic variation was assessed through the estimation of the parameter ‘heritability’. The heritability (h ²) of total number of oocytes was zero, but large heritability values were seen for mean oocytes diameter (h ²=0.57±0.27) and OM (h ²=0.71±0.26). Family means correlations between traits in subadults with traits measured in their full-sibs when adults (days to first spawn, total number of spawns, total fecundity, and fecundity at first spawn) indicated the existence of some significant associations between reproductive traits at the two ages. These findings point toward an early genetic determination of reproductive capacity in this crustacean.     

Purification and immunolocalization of a vitellin-like protein from the Pacific oyster Crassostrea gigas

A female-specific protein from the hemolymph, and a related ovarian protein were identified in the Pacific oyster Crassostrea gigas using immunological procedures. The latter protein was isolated from ovarian extract by a combination of precipitation in distilled water, ammonium sulfate fractionation, hydroxylapatite chromatography and gel filtration on a Sepharose 6B column, and was identified as a macromolecular glycolipoprotein of 500 kD; sodium dodecylsulfate polyacrylamide gel electrophoresis, under reducing conditions, revealed seven heterogeneous polypeptides. Using a specific antiserum against purified protein, we also examined the immunohistochemical distribution of the protein at light- and electron-microscopic levels. Light microscopy revealed its presence in the oocytes, and electron microscopy identified it in yolk granules and the vitelline coat of the oocytes. These results indicate that the purified protein is a vitellin-like protein. Since no organ other than the ovary reacted with the antiserum, it is probable that the protein is produced inside the ovary, probably autosynthetically by oocytes.     

Reproductive biology of the lanternfish Benthosema pterotum from the Indian Ocean

Samples of Benthosema pterotum (Alcock) were obtained from the Arabian Sea (1976, 1979, 1981, 1983, 1984), off Mozambique (1978) and from the Bay of Bengal (1979). The sexual maturity stages are described. For females, the size of the largest oocytes was found to be most useful for size of the largest oocytes was found to be most useful for assessing maturity. Mature and spawning fish were found in all seasons. Samples from November 1983 differed from all others in having very few mature females. A few apparently spent fish were observed in July to August 1979 and November 1983. Some females mature at 25 mm and males at 20 mm, whereas others can still be immature at 45 and 40 mm, respectively. Of the total number of stations, four had significantly more males than females, twelve significantly more females, and forty-seven displayed no difference in the sex ratios. The vertical migration of the mature and spawning fish did not differ significantly from that of other individuals. Batch fecundity ranged from ca. 200 to 3 000 eggs fish ranging from 27 to 52 mm, relative fecundity from ca. 2 000 to 7 000 eggs g^-1 maternal dry weight. There are indications that B. pterotum spawns only once, but no firm conclusions could be drawn.     

Comparative fertilization biology of gymnolaemate bryozoans

Locations and oogenic stages of eggs at the time of sperm-egg fusion were determined for nine gymnolaemate species exhibiting different reproductive strategies with respect to site of embryonic development (e.g., water column, introvert, embryo sac, or ovicell) larval type, and zooid sexuality. Ovarian, coelomic, and recently spawned oocytes obtained from freshly collected colonies between 1988 and 1995 were stained with aceto-orcein and examined for the presence of a sperm nucleus. All nine species are shown to have a similar fertilization biology in which sperm fuse with eggs in or near ovaries and egg activation is delayed until eggs are spawned. In species such as the etenostomeAlcyonidium sp. and the cheilostomeElectra pilosa (Linnaeus, 1767), which produce marierons oocytes that are spawned into the water column and have cyphonautes larvae, sperm fuse with late growth stage ovarian oocytes after germinal vesicle breakdown (GVBD) at or near ovulation. In species that produce few oocytes, brood embryos, and release coronate larvae, sperm fuse with late growth stage ovarian primary oocytes before GVBD, as in the ctenostomeBowerbankia gracilis Leidy, 1855, or with very early growth stage ovarian primary oocytes, as in the cheilostomesCribrilina corbicula (O'Donoghue, 1923),Dendrobeania lichenoides (Robertson, 1900),Hippodiplosia insculpta (Hincks, 1882),Schizoporella serialis (Heller, 1867),T ricellaria gracilis (Smitt, 1867), andWatersipora arcuata Banta, 1969. Fertilization success was high in all nine species, with 83 to 100% of oocytes at an appropriate oogenic stage containing a sperm nucleus or early male pronucleus. Gymnolaemate bryozoans may maintain high levels of fertilization success by: (1) concentrating spawned sperm from the water column using colony feeding currents; (2) localizing sperm-egg encounters in or near the ovary, (3) using sperm when available by permitting sperm to fuse with early growth stage oocytes; and (4) selfing.     

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.     

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.     

Multiple spawning in the tropical squid Photololigo sp.: what is the cost in somatic growth?

This study assesses the potential of the tropical loliginid squid Photololigo sp. to lay multiple batches of eggs and examines changes in somatic growth during reproduction. Histological analysis of the ovary and the relative size of the oviduct to mantle weight and ovary weight were used to determine the potential for multiple spawning. Ovaries of mature females always had immature and mature oocytes present, suggesting that not all the oocytes were maturing simultaneously and that multiple batches of eggs were being produced. Furthermore, poor correlations of oviduct weight with body size and ovary weight indicated that mature oocytes were not accumulating in the oviduct for a single spawning event. Both these observations supported the hypothesis that Photololigo sp. has the potential to lay multiple batches of eggs throughout its life. Specific growth rates, length-weight relationships, relative growth of somatic and reproductive tissue and microscopic assessment of muscle tissue were compared between immature and mature females. Growth rates of immature females were almost twice as fast as those of mature females. Mature females also had no large muscle fibres present, suggesting that energy for reproduction was mobilised from the muscle tissue.     

Evidence for multiple spawning in the tropical oceanic squid Stenoteuthis oualaniensis (Teuthoidea: Ommastrephidae)

Indirect evidence suggests that Stenoteuthis oualaniensis is a multiple spawner, a reproductive strategy not reported previously for squid. After spawning once, S. oualaniensis apparently continues to feed, grow, and mature additional oocytes before spawning again. Squid were caught by jigging at night in waters around the main Hawaiian Islands during four cruises from 1981 to 1987. All females from 200 mm mantle length (ML) to at least 318 mm ML were sexually mature, indicating that considerable growth takes place after reaching sexual maturity. Size-frequency analyses of ovarian oocytes revealed continuous egg production throughout adult life. Mature ova are stored in the oviducts, but oviduct fullness is unrelated to body size, indicating repeat spawning.     

Growth and reproductive biology of the small penaeid shrimp Trachysalambria curvirostris in Tokyo Bay

We investigated the growth and reproductive biology of the penaeid shrimp Trachysalambria curvirostris in Tokyo Bay, Japan, by monthly bottom-trawl surveys from May 2002 to December 2004. We also examined oogenesis in T. curvirostris by histological observation of the ovary. Females grew faster and attained a larger body size for age than males. The growth rate was high in summer and low in winter and was likely to be associated with seasonal changes in water temperature. The carapace length (CL) at which 50% of females contained vitellogenic oocytes was estimated to be 17.0 mm. The reproductive season extended from May to October. Young-of-the-year appeared in October and could be traced across the months on CL histograms to the following September or October, indicating a 1-year life cycle. This extended reproductive season, together with our observation of asynchronous development of oocytes in the ovary, suggests that multiple spawning by individual females may occur during the reproductive season. Postovulated oocytes were not found among the samples we collected during the daytime, suggesting that final oocyte maturation and spawning occur at night. Cortical crypts in the cytoplasm of the oocyte, considered to be a general feature of oogenesis in penaeid shrimps, were not found in T. curvirostris, even in oocytes undergoing germinal vesicle breakdown. This result implies that the cortical reaction after spawning of T. curvirostris may be different from that of other penaeid shrimps.     

The reproductive biology of Hymenaster membranaceus from the Rockall Trough,North-East Atlantic Ocean,with notes on H. gennaeus

Samples of the deep-sea spinulosan asteroid Hymenaster membranaceus Wyville Thomson were collected in a timeseries of 19 bottom trawls spanning the period April 1978 to October 1981 from a 2200 m-deep station in the northern Rockall Trough. The reproductive biology of this species was studied from histological sections of the gonad, and compared with that of H. gennaeus H. L. Clark which was collected in the same hauls. At first sexual development, oogonia develop in nests surrounded by small accessory cells. Previtellogenic oocytes remain in the periphery but, at maturity, oocytes ranging up to 1 100 m fill the ovary. A variety of accessory cells pack the lumen and may be nutritive or degenerative. It appears that a small number of oocytes are spawned intermittently, but there is no evidence of overproduction and break-down of superfluous oocytes. A few large oocytes become senescent and undergo internal break-down, releasing periodic acid Schiff-positive material into the lumen. Size-frequencies of oocytes indicate that eggs may be spawned as a continuous slow release, and there is no evidence of reproductive synchrony between or within samples. On reaching maturity, males appear always to be ready to release spermatozoa. Spawning is probably stimulated by egg release during chance encounters with mature females. There is no evidence for brooding, and from the large size and yolky nature of the egg direct lecithotrophic development at or near the seabed is inferred. A limited histological study of H. gennaeus indicates that egg production is very similar, but the two species differ in the nature of the accessory cells and amorphous material filling the lumen.     

Changes in the biochemical composition of the ovaries of the seastar Asterias rubens during its annual reproductive cycle

The biochemical composition of the ovaries of the asteroid echinoderm Asterias rubens was studied, with emphasis on the changes which are manifest during the annual reproductive cycle. Ovarian dry weight displays only minor changes during ovarian development, constituting about 20% of the organ fresh weight. Levels of all constituents show some variation, but in general increase with ovarian growth. Only the free amino acid level is rather constant. Except for glycogen, the contents of other constituents (total lipids, other reducing sugars, free amino acids and proteins) show a rectilinear increase with ovarian growth. Glycogen content increases rectilinearly with time during early vitellogenesis, but remains constant during further development until ovarian maturity. By plotting constituent levels and contents against a non-linear gonad index axis rather than against sampling date, results can be correlated more easily with ovarian growth stages. The possibility of endocytosis of a vitellogenin-like yolk precursor by the ovary is discussed.     

Sex and reproductive aspects in Serranus cabrilla (Osteichthyes: Serranidae): macroscopic and histological approaches

The gonads of Serranus cabrilla (Linnaeus, 1758) from the Canary Islands were studied between September 1992 and July 1993. Macroscopic classification of the maturity stages was compared with histolog ical classification of gonad characteristics, and the effect␣of the classification method on the determination of the spawning season and size at maturity was investigated. Analysis of gonad organization and development confirmed that this species is synchronously hermaphroditic. Ovarian-tissue development is asynchronous, and testicular tissue consists of continuous spermatogonia. Six stages of oogenesis and five of spermatogenesis are described, based on differences in staining and in size and on differences in the nucleus and cytoplasm structure as viewed through a light microscope. Two types of atretic degeneration of eggs are also described. Agreement between macroscopic and histological staging was low, although both methods provided similar results in spawning-season determination and size at maturity. The spawning season of S. cabrilla is from February to July, with a peak in May. Fish size at first maturity (size at which 50% of all fish sampled are in relevant maturity stage) is 152 mm standard length (SL), and size at mass maturity (size at which 95% of all fish sampled are in relevant maturity stage) is 167 mm SL. Received: 21 May 1996 / Accepted: 9 August 1996     

Evaluating ultrasonography as a non-lethal method for the assessment of maturity in oviparous elasmobranchs

Due to the impacts of commercial fishing on elasmobranchs, future research and management necessitates reliable and accurate information on life history. For females, maturity assessment is limited to dissection, and it is not desirable to be removing large numbers in order to assess the reproductive characteristics of a population. The present study evaluated ultrasonography as a potential, non-lethal method for assessing the maturity status of two oviparous elasmobranchs, the thornback ray (Raja clavata) and small-spotted catshark (Scyliorhinus canicula). Ultrasound permitted visualisation and measurement of the ovary in R. clavata, and the shell gland, ovarian follicles and egg capsules within the oviducts for S. canicula. With the exception of the ovary in R. clavata, the dimensions of these structures on the sonograms were directly corroborated by in situ measurements, and ultrasound was verified as an accurate and reliable method of making quantitative and qualitative assessments of these internal reproductive structures.     

Dynamics of de novo vitellogenesis in fish with indeterminate fecundity: an application of oocyte packing density theory to European anchovy, <Emphasis Type="Italic">Engraulis encrasicolus</Emphasis>

De novo vitellogenesis is common among teleosts; however, its dynamics and the timing of batch recruitment are poorly understood. In this study, we combine a suite of methods and theories in fish reproductive biology (oocyte packing density, stereology, ovarian allometry, oocyte size frequencies and postovulatory follicle [POF] ageing) to reconstruct the steps and timing of batch recruitment in European anchovy. Using general linear modelling to standardize oocyte numbers, we demonstrate that the fractions of primary growth, cortical alveoli and vitellogenic oocytes in the ovary are relatively stable in females with migratory nucleus oocytes (MN) or with POFs 1 and 2 days old (POF-1 and POF-2), but they change abruptly at hydration. These results imply that batch recruitment in European anchovy occurs in pulses of very short duration (less than a day). The standing crop of vitellogenic oocytes in MN, POF-1 and POF-2 females equals the number of eggs contained in two mature batches.