Ovarian morphology and oogenesis in Aurelia aurita (Scyphozoa: Semaeostomae): ultrastructural evidence of heterosynthetic yolk formation in a primitive metazoan

In Aurelia aurita, the ovaries arise as horseshoe-shaped evaginations of the gastrodermis in the floor of four interradial gastric pouches. Germ-cell islands arise within endodermally-derived gastrodermal cells. Oocytes grow and gradually bulge into the mesoglea while maintaining physical contact throughout vitellogenesis with specialized cells called trophocytes. Ultrastructural changes suggest that these cells transport yolk precursors from the coelenteron to the oocytes in a manner similar to that reported for the trophonema cells of anthozoan ovaries. Vitellogenesis involves both the autosynthetic activity of the oocyte organelles (Golgi complex and rough endoplasmic reticulum) and the heterosynthetic incorporation of precursors through endocytotic processes involving both coated pits and vesicles and smooth-surfaced tubules. Ultrastructural data suggest that different types or classes of yolk precursors enter the oocyte through the trophocytes and via the surrounding mesoglea. To our knowledge, this is the most primitive animal in which this type of yolk synthesis has been described. The trophocyte-oocyte relationship in oocytes of A. aurita is reminiscent of the trophonema-oocyte relationship in anthozoans and supports the belief that the Anthozoa and Scyphozoa share a close phylogenetic relationship.     

Flow and feeding by swimming scyphomedusae

The mechanical basis of prey capture by scyphomedusae has been largely ignored, despite the importance of these predators in a variety of planktonic ecosystems. Interactions between swimming, fluid motions, and prey capture were examined during 1991–1992 for a species from the three scyphozoan orders having planktonic medusae: Rhizostomeae, Stomolophus meleagris Agassiz, 1862; Coronatae, Linuche unguiculata (Schwartz, 1788); and Semaeostomeae, Cyanea capillata (Linnaeus, 1758). All three species used flow created during bell pulsation to capture prey, but the type of flow used for prey capture and the capture surface morphology were different for each species. The mechanics of capture by these species of diverse morphology and taxonomic affinity suggests that the use of bell pulsation-induced flow for prey entrainment and capture is widespread among the scyphomedusae.     

Organ-like gonads, complex oocyte formation, and long-term spawning in Periphylla periphylla (Cnidaria, Scyphozoa, Coronatae)

An account is given about the development of the gametes of the holopelagic coronate scyphomedusa Periphylla periphylla (Péron and Lesueur 1809). The gonads of the species are complex and differ from those thus far described in Scyphozoa in having this characteristic composition of trophocytes, follicle cells, gamete-releasing pores, mucus cells, and resorption cells. Our results differ from those of previous coronate studies with respect to the contact of the oocytes with the gonad tissue throughout the duration of development. Among the Medusozoa, follicle cells have thus far been considered as an apomorphy for the Staurozoa, but their presence in the Scyphozoa casts some doubts on this assumption. From morphological structure and examination of the gonads and gametes, it can be deduced that P. periphylla has true organs and that gamete release is continuous. These results supplement our knowledge of the reproductive biology of this mesopelagic species.     

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.     

Reproduction and reproductive variability in the coral Pocillopora verrucosa from the Republic of Maldives

The sexuality, reproductive mode, and timing of reproduction of Pocillopora verrucosa from the Republic of Maldives, Indian Ocean, were assessed using serial histological sections. These showed that P. verrucosa is an annual simultaneous hermaphrodite, with gonads arranged in two opposing arcs of alternating testes and ovaries, six gonads in each arc. No planulae were observed in any dissection or histological analysis carried out, therefore making brooding unlikely. Broadcast spawning is inferred from the disappearance of mature gametes from samples collected between late March and April 1991. Mean oocyte size at spawning was 53.5 m and mean potential fecundity was 7300 ooctyes cm^-2yr^-1. The reproductive pattern of P. verrucosa in the Maldives is compared to that of the same species in different locations, the short breeding season in March to April occurring earlier in the Maldives than in Red Sea populations. The maximum mean oocyte diameter found in Maldivian specimens was much smaller than elsewhere. The year-to-year variation in numbers of oocytes/polyp within single colonies, and the variation between colonies within the population was significant (p<0.01). Therefore, it is possible that fecundity is not a good variable to use when monitoring stress on coral reefs unless larger numbers of estimates can be routinely made. Some colonies contained immature oocytes at spawning that were not released and continued to grow to approximately twice the size of the spawned oocytes that were presumed to be mature. These unspawned oocytes were oosorbing, and were characterised by the presence of zooxanthellae and large numbers of vacuoles in their cytoplasm. This gradual expansion and oosorption of unspawned oocytes has not been documented previously for corals.     

Reproduction in Anthelia glauca (Octocorallia: Xeniidae). II. Transmission of algal symbionts during planular brooding

The soft coral Anthelia glauca Lamarck, 1816, of the family Xeniidae, is found on the reefs of KwaZulu-Natal, South Africa. Its gastrodermal cells contain numerous endosymbiotic unicellular algae (zooxanthellae). A. glauca is a gonochoric species that simultaneously broods its planulae within the pharyngeal cavity of the polyps. Symbiotic algae appear with zygote formation within the pharynx, embedded in amorphous material. The algal cells adhere to the ciliated ectodermal surface of immature planulae and are most probably endocytosed by them. Zooxanthellae are translocated towards the basal part of the ectoderm. Gaps are subsequently opened in the mesoglea into which symbionts surrounded by ectodermally derived material, including plasma membrane, pass. The basal membrane of endodermal cells disintegrates, and the algae bulge into spaces formed in the underlying endoderm. Throughout the process, each zooxanthella resides within a vacuolar membrane in the detached ectodermal cytoplasm. The acquisition process is essentially one in which zooxanthellae are translocated from the pharyngeal cavity into the ectoderm and then through the mesoglea into the endoderm, culminating in the final symbiotic state. The direct transmission of symbiotic algae to the eggs or larvae probably provides the most efficient means whereby zooxanthellae are acquired by the host progeny. Received: 15 July 1997 / Accepted: 25 February 1998     

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.     

Invading <Emphasis Type="Italic">Aurelia aurita</Emphasis> has established scyphistoma populations in the Caspian Sea

The Caspian Sea has no endemic Scyphozoa. In 1999, a mass accumulation of Aurelia medusae was recorded, indicating that sometime earlier, jellyfish had invaded the basin, but since then no scyphozoans have been reported in the Caspian. In the fall of 2008, we found scyphistomae (scyphoid polyps) during a cruise to the eastern Middle Caspian. The scyphistomae were numerous (100–10,000 ind. m⁻²) and occupied a depth range of 30–73 m. Genetic data (18S rDNA, ITS-1 and COI) showed that the scyphistomae belonged to the species A. aurita. The current genetic data set is insufficient to determine the source region(s) of the invasive A. aurita. It remains unclear why no moon jellies have been recorded in the Caspian in the last 10 years. Because swarming scyphomedusae are often pests, the presence of scyphistomae should be considered as a warning of a possible outbreak of A. aurita medusae in the Caspian.     

Sexual reproduction in solitary corals: Overlapping oogenic and brooding cycles,and benthic planulas in Balanophyllia elegans

The temperate solitary coral Balanophyllia elegans Verrill, 1864 was collected monthly between January 1977 and August 1978 off the California coast. B. elegans reproduces only sexually, is gonochoric, and broods its embryos. Males are ripe only in late summer, but oocytes and embryos (ca. 40 per female) are found throughout the year. The presence of oocytes and embryos throughout the year may be the result of very long, overlapping oocyte growth and embryonic developmental times. Large, crawling, benthic planulas are released mainly in the winter. The skeletal design of the corallum of B. elegans accommodates the brooding of unusually large embryos; this design may be indicative of brooding large embryos in other species of corals, particularly dendrophyllids.     

Reproductive biology of the edible jellyfish Catostylus mosaicus (Rhizostomeae)

 The reproductive biology of the jellyfish Catostylus mosaicus (Quoy and Gaimard 1824) (Scyphozoa: Rhizostomeae) was investigated in New South Wales, Australia. Medusae were gonochoristic. There was a 1:1 ratio of male and female medusae and there was no evidence of sexual dimorphism. Oocytes arose from the gastrodermis and maintained contact with the gastrodermis, via trophocytes, throughout gametogenesis. Spermatogenesis occurred within follicles that arose from invagination of the gastrodermis. Detailed sampling of gonads over a period of 3.25 yr in Botany Bay, and over 2.5 yr in Lake Illawarra, indicated that gametogenesis occurred almost continuously during the year. Oocytes were smaller, or were absent from the ovaries during 3 of the 4 winters sampled at Botany Bay and during all 3 winter periods sampled at Lake Illawarra. Comparisons were made with other locations, although these were sampled less frequently. When medusae were present at a location, similar trends were observed. The size at which medusae matured varied, but during non-winter periods and at two locations, all medusae exceeding 130 mm diam were considered mature. Received: 6 January 2000 / Accepted: 3 July 2000     

The reproductive biology of echinothuriid and cidarid sea urchins from the deep sea (Rockall Trough,North-East Atlantic Ocean)

The reproductive biology of 5 species of echinothuriid (Phormosoma placenta, Calveriosoma hystrix, Araeosoma fenestrum, Sperosoma grimaldii and Hygrosoma petersii) and 2 species of cidarid (Cidaris cidaris and Poriocidaris purpurata) sea urchins from the deep sea (Rockall Trough) has been examined from samples collected during 1973–1983. In all species the gonads lie within the interambulacrum attached to aboral gonopores and when fully developed occupy most of the test not occupied by the gut or Aristotle's lantern. In all the species, initial oocyte development takes place along the germinal epithelium embedded in nutritive tissue. In all the echinothuriids and in Poriocidaris purpurata, the oocyte grows to ca. 200 to 450 m, at which stage vitellogenesis begins. Oocyte growth continues until a maximum egg size of 1 100 to 1 500 m is attained. In the echinothuriids, two types of nutritive tissue are found. In the carly stages of gametogenesis the oocyte is surrounded by well-structured periodic acid Schiff (PAS)-positive tissue. As the oocyte grows this tissue becomes vacuolated, suggesting that there is a transfer of nutriment to the developing oocyte. In Phormosoma placenta, unspawned oocytes are phagocytosed. There is no evidence of seasonality in any of the echinothuriid species or in Poriocidaris purpurata. Extrapolation with shallow-water echinothuriids suggests that larval development is lecithotrophic, omitting any planktotrophic phase. Of the species examined, only Cidaris cidaris has a reproductive strategy which produces a known larva, although the limited samples did not permit any determination of seasonality in this deep-sea population.     

Oogenesis in the marine mussel Mytilus edulis: an ultrastructural study

Ultrastructural changes occurring during the course of development in oocytes of Mytilus edulis are described for mussels collected at monthly intervals over a period of one year (September 1981 to October 1982) from a site in Cornwall, England. During early stages of oogenesis the oocyte is surrounded by a small number of follicle cells but, as development proceeds, the follicle cells are restricted to the stalk region which attaches the oocyte to the acinar wall. Contact between the follicle cells and the developing oocyte is maintained by means of desmosomelike gap junctions. Organelles and inclusion bodies present in the ooplasm during oogenesis include rough endoplasmic reticulum (RER), Golgi bodies, mitochondria, free ribosomes, Balbiani's vitelline body, annulate lamellae and yolk and cortical granules. The RER, in particular, varies considerably throughout the course of development. Evidence for uptake of exogenous macromolecules into oocytes by pinocytosis is presented; it occurs in the basal region of previtellogenic oocytes prior to the formation of the vittelline coat. Lipid-yolk granules invariably have mitochondria in close association and, during the winter months, develop in close proximity to small, apparently glycogen-rich vesicles possibly suggesting that conversion of glycogen to lipid takes place in developing oocytes. Oocyte degeneration was commonly observed and involves initial breakdown of the plasma membrane followed by rupture of the vitelline coat. The oocyte contents once released into the acinar lumen are resorbed by the epithelial cells of the gonoducts, which are prevalent throughout the mantle of ripe individuals.     

Utrastructural study of oogenesis and oocytic degeneration in Pecten maximus from the Bay of St. Brieuc

An ultrastructural study of oocytic development enabled the identification of changes occurring during oogenesis in Pecten maximus collected from the Bay of St. Brieuc, France, in 1987. Auxiliary cells, closely associated with developing oocytes were observed. Each oocyte seems to be associated with only one secretory cell, which is characterised by an abundant rough endoplasmic reticulum at the onset of vitellogenesis. Contact between this cell and a developing oocyte is maintained by a desmosome-like junction which can be observed when the vitelline coat is formed. These auxiliary cells seem to play a trophic role in vitellogenesis, and may be involved in the formation of the vitelline coat of the oocytes. Oocytic degeneration is discussed in detail; in this species, it is a continuous phenomenon of varying intensity throughout the year. The ultrastructural changes resulting in lysis of the oocyte are described, and the evolution of atretic oocytes is examined.     

Oocyte development in the kuruma prawn Penaeus japonicus

Female kuruma prawns (Penaeus japonicus Bate) with undeveloped, early developing, developing, nearly ripe and ripe ovaries, were collected from Ise Bay, Japan, in 1984. Oocyte development of the kuruma prawn was classified into ten stages according to morphological characters, namely: (1) synapsis stage, (2) chromatin nucleolus stage, (3) early perinucleolus stage, (4) late perinucleolus stage, (5) oil globule Stage I, (6) oil globule Stage II, (7) yolkless stage, (8) yolk granule stage, (9) prematuration stage, and (10) maturation stage. The synapsis stage is a multiplication stage. The chromatin nucleolus stage, early and late perinucleolus stages are previtellogenesis and primary growth stages. Oil globule Stage I is an initial stage of primary vitellogenesis and secondary growth. Follicle cells on the oil globule Stage I oocytes expand rapidly and reach maximum size during oogenesis. Yolk granule stage oocytes are in the initial stages of secondary vitellogenesis. Strongly acidophilic yolk granules accumulate within basophilic vesicles of the cytoplasm. The yolk granules are first concentrated in the inner part of the cytoplasm, then gradually spread to the periphery. Cortical crypts, which are separated from the oocyte cytoplasm by the cytoplasmic membrane, are situated outside of oocyte cytoplasm. Germinal vesicle breakdown (GVBD) is initiated in the late phase of prematuration and continues until the late phase of maturation immediately prior to spawning. At the beginning of the maturation stage, the oocytes are ovulated, after which the nuclei further shrink and migrate out-wards. After ovulation, meiotic division of the ovarian oocyte progressed up to the metaphase of primary maturation division. Finally, the meiotic metaphase is visible just beneath the cytoplasmic membrane in the mature oocyte. Though ovulation is synchronous within the same ovary, GVBD is not completely synchronous. Ovulated mature oocytes have many club-shaped cortical crypts in the peripheral part of the cytoplasm and contain extensive accumulations of yolk granules dispersed throughout the cytoplasm. The apical end of the club-shaped cortical crypts and cytoplasmic membrane are coated by the vitellin envelope in the mature oocyte.     

Transmission of symbiotic dinoflagellates through the sexual cycle of the host scyphozoan Linuche unguiculata

Intracellular symbiotic dinoflagellates are associated with the tropical scyphozoan Linuche unguiculata (Swartz, 1788) throughout all stages of the host's life cycle. During sexual reproduction, eggs are released in mucus strands that contain symbiotic dinoflagellates. Fertilization and development take place externally in the water column. Epifluorescence and transmission electron microscopy showed that unfertilized eggs did not contain intracellular algae, but that infection of the developing embryo was generally successful by the 128-cell stage (10 h after fertilization at 23° C). However, experiments with artificially provided Cellufluor-labeled algae demonstrated that older embryos and planulae could be infected by algae through at least 24 h post-fertilization, indicating that the L. unguiculata symbiosis represents a semi-closed system. This novel mode of symbiont acquisition results in most sexually-produced offspring becoming infected with maternally-transmitted algae during early development, but allows for acquisition of non-maternally-provided algae later in development. Most of the algal symbionts during the early stages of embryonic and larval development are located within ectodermal cells. This is in contrast to the other life-cycle stages of L. unguiculata (i.e., scyphistoma, medusa, ephyra), where symbionts are found within the gastrodermis of the host.     

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.     

Relationships between the movements,growth, age structures,and reproductive biology of the teleosts Sillago burrus and S. vittata in temperate marine waters

Sillago burrus and S. vittata both use sheltered, nearshore shallow waters ( 1.5 m) as nursery areas. However, the juveniles of the former species remain there for only a few months, before migrating into deeper waters (5 to 15 m) as they increase in size, whereas some juvenile S. vittata do not undergo a similar migration until considerably later. S. burrus rarely exceeded 2 yr of age and was never found beyond 4 yr of age. Although only a small number of S. vittata exceeded 2 yr of age, a few individuals of this species were caught between 4 and 7 yr old. The maximum and asymptotic lengths of S. burrus (251 and 180 mm, respectively) were far lower than those of S. vittata (325 and 320 mm, respectively), whereas the growth coefficients (K) were much higher for the former species, i.e. 2.4 vs 0.4. Virtually all S. burrus, and also those S. vittata that moved into deeper waters early in life, spawned at the end of their first year of life. Since relatively few S. burrus reached 2 yr of age, the attainment of almost full size by the end of their first year of life enables a relatively large number of eggs to be produced by fish at the end of their first year-for many, their only spawning period. Those individuals of S. vittata that remained in their shallow nursery areas until the end of their first year of life, did not reach maturity until the end of their second year of life. The proportions of mature gonads and the numbers of yolk-vesicle and yolk-granule oocytes and post-ovulatory follicles in ovaries were far higher in both S. burrus and S. vittata during December to February than in any other month, demonstrating that these two species spawn largely in these summer months. During this period, the ovaries of individual S. burrus and S. vittata often contained post-ovulatory follicles, as well as yolkvesicle and yolk-granule oocytes that ranged widely in size, strongly suggesting that both species are multiple spawners. During the spawning period of S. burrus, the ovaries possessed large numbers of hydrated oocytes and no post-ovulatory follicles or the reverse situation, and the oocytes tended to form several relatively discrete size groups. This indicates that S. burrus produces eggs in batches and that the spawning of the members of this species is synchronised. The presence of large numbers of yolk-granule oocytes with migrating nuclei in the ovaries of many S. vittata at certain times suggests that this species is also a batch- and synchronised spawner. Comparisons between the results of the present study and past work emphasise that the relationships between the timing of offshore movements and the sizes and ages at first maturity vary considerably amongst whiting species.     

Reproductive strategies of two deep-sea gastropod species from the Porcupine Seabight (Northeast Atlantic)

Two species of small gastropods (<6 mm in length), Amphissa acutecostata (Philippi, 1844) and Gymnobela subaraneosa (Dautzenberg and Fischer, 1896), widely distributed in the northeast Atlantic, were found in large numbers in the Porcupine Seabight (Northeast Atlantic). Except for some aspects of taxonomy and distribution, as well as some data on larval development, the biology of these species is unknown. This study describes basic aspects of the life-history strategies of both species. Histological studies showed that oocyte and sperm development in both species was similar to the gametogenetic patterns observed in other deep-sea gastropods. In females, oogonia proliferated in the germinal epithelium and developed into previtellogenic oocytes (30–40 m), which grew into vitellogenic primary oocytes. Vitellogenic oocytes were covered by a thin layer of follicle cells involved in the vitellogenic processes. The maximum size for mature oocytes was 99.06 m for A. acutecostata and 114.82 m for G. subaraneosa. In A. acutecostata most of the volume of the ovary was occupied by previtellogenic and early vitellogenic oocytes, whereas in G. subaraneosa most of the volume was filled by large vitellogenic oocytes. Both species showed quasi-continuous production of oocytes. The oocyte size-frequency diagrams suggested a continuous release of a small number of oocytes throughout the year for A. acutecostata, and asynchronous periodic spawning events for G. subaraneosa. Gonad development and gametogenesis could be strongly affected by presence of parasites in one of the populations of G. subaraneosa.Communicated by J.P. Thorpe, Port Erin     

Observations on the reproductive cycles of Monodonta lineata,Gibbula umbilicalis and G. cineraria

Monthly samples of gonads of 3 common species of intertidal trochids, Monodonta lineata (da Costa), Gibbula umbilicalis (da Costa) and G. cineraria (L.) were fixed for examination by light microscopy. Numbers and proportions of immature and mature oocytes in sections of ovaries were determined. In M. lineata and G. umbilicalis, the annual reproductive cycles were very similar, the testis and ovary of both species being empty brown structures from September to January/February, when gametogenesis began and the gonads began to swell and turn green in both sexes. As ripening continued, the ovary remained green in G. umbilicalis, but in M. lineata turned greygreen by the end of May. The testis of both species changed, to yellowish in G. umbilicalis and creamy-pink in M. lineata. Spawning occurred throughout summer and early autumn, and the gonads reverted to their former empty state. These changes were matched by the increase and subsequent decrease in proportion of ripe oocytes in the gonad. Some ripe oocytes are not shed during the spawning season, but no evidence of cytolysis of such oocytes was found. In G. cineraria, in contrast, the ovary remained green and swollen and the testis remained creamy-white and packed with sperm throughout the year. The proportion of ripe to unripe oocytes in the ovary fluctuated for the entire sampling period, and did not indicate the time of spawning. In the testis of all three species, spermatogonia were rarely seen, and spermatid stages were uncommon.     

Fecundity of the chokka squid Loligo vulgaris reynaudii on the southeastern coast of South Africa

Potential fecundity in Loligo vulgaris reynaudii was estimated to be about 17 000 eggs, calculated as the total number of discernible oocytes in the ovary and oviduct. Squid were observed to spawn up to 8140 eggs over a 36 h period in captivity. First estimations of actual fecundity are therefore between 8000 and 17 000 eggs. Factors complicating a more accurate estimation of actual fecundity in this species include difficulties with aquarium maintenance, their behaviour of spawning over a protracted period and in multiple sites, and atretic oocytes observed in both developing and mature ovaries. Detailed morphological and histological analysis of gonads collected at regular intervals over a complete spawning season will allow a more precise calculation of actual fecundity. Received: 9 October 1998 / Accepted: 22 April 1999