Transition zone in otoliths of orange roughy (Hoplostethus atlanticus) and its relationship to the onset of maturity

A transition zone in the otoliths of orange roughy (Hoplostethus atlanticus) is described where annulus width decreases markedly. For fish sampled at spawning time, the relationship between gonad stage and the presence or absence of a transition zone is consistent with the hypothesis that this zone marks the onset of maturity, if allowance is made for some error in gonad staging and identification of the zone. Another data set from a non-spawning area after the spawning season is not consistent with the hypothesis. However, these latter data are considered less reliable because of the small size of the fish in the sample and difficulties in determining, outside the spawning season, whether a fish has been reproductively active. This hypothesis was used to provide estimates of the median age (30 yr) and length (31 cm) at the onset of maturity for the Chatham Rise, New Zealand population. These estimates are unaffected by the biases associated with the usual ogive method of estimation. Received: 27 June 1997 / Accepted: 1 July 1997     

Reproduction and growth of Isostichopus fuscus (Echinodermata: Holothuroidea) in the southern Gulf of California, México

The reproduction and growth of Isostichopus fuscus (Ludwig, 1875) at Isla Espíritu Santo, Baja California Sur, México from July 1992 to September 1993 and from August 1996 to July 1997 were analyzed. The reproductive cycle was monitored by using histological analysis. Five gonadal stages were described according to cell types present in the gonad; undetermined, gametogenesis, maturity, spawning and post-spawning. This holothurian reproduces annually during summer (July to September), when sea surface temperature reaches 27 °C. The gonad index is related to the gonadal stages. The first sexual maturity for I. fuscus was calculated at 367 g (4 to 5 years old) according to the von Bertalanffy equation, and nearly all the specimens at Isla Espíritu Santo were 5 to 7 years old (including some individuals over 35 years old). Data of the length–weight relationship showed that I. fuscus grows allometrically at the studied site (b = 1.83). The mortality rate was relatively high (M = 0.51), indicating that in a typical cohort, 40% of the recruits does not survive the first year, and less than 20% reaches maturity. Received: 15 July 1998 / Accepted: 19 August 1999     

Reproductive biology of the commercial sea cucumber Holothuria fuscogilva in the Solomon Islands

 Reproduction of Holothuria fuscogilva (Selenka, 1867) in the Solomon Islands was investigated over a 4 yr period (1994 to 1998) by macroscopic and microscopic examination of the gonad tubules, the gonad index (GI) method, histological examination of gametogenesis, and spawning-induction trials. The gonad consisted of numerous tubules that dominated the coelom of gravid specimens. New tubules appeared in March, and grew in size and extent of branching until they reached their maximum size and maturity in August. Spawning occurred from August to October, with the majority of gametes released during October, although it was only partial in many individuals. After spawning, the tubules appeared wrinkled and resorbed into the gonad basis. A five-stage gonad maturity scale based on the macroscopic appearance of the gonad tubules corresponded with discrete stages of gametogenesis identified by histology. Gametogenesis was initiated in mid-March, with oogenesis and spermatogenesis occurring in parallel, followed by the growing stage (May to July) which was marked by active gamete development. Successful induction of spawning during the breeding period corroborated the GI and histological data. The uniform growth of gonad tubules indicated that H. fuscogilva in the Solomon Islands does not conform to the progressive tubule recruitment model described for other holothurians. An important application of this study is that the appearance of gonad tubules, removed by biopsy, can be used to determine the gonad condition of wild adults or captive broodstock. Received: 28 June 1999 / Accepted: 8 March 2000     

Sexual reproduction of the reef coral Montastreacavernosa (Scleractinia: Faviidae) in the Santa Marta area, Caribbean coast of Colombia

Sexual reproduction of the reef-building coral Montastreacavernosa was studied in the Santa Marta area, Caribbean coast of Colombia, from October 1990 to October 1991. The area is subjected to a seasonal upwelling–outwelling regime. From microscopical analysis of tissue sections sampled each lunar month around the full moon, it was confirmed that this is a gonochoric, broadcasting species, with a single gametogenic cycle per year, and a 1:1 sex ratio. Oogenesis began a few weeks after spawning, and extended for 11 mo. The onset of spermatogenesis occurred just before the full moon of June, later than at other localities where sea-water temperatures during the first half of the year are not as low. The amount of reproductive tissue strongly increased in both sexes after July, in association with an increase in sea-water temperature and a decrease in photoperiod. The gonad index of fully mature female colonies was about four times lower than at other localities, perhaps due to the stressful seasonal regime. The male gonad index was lower than that of the female, indicating sex-related differences in the rates of biomass allocation to reproduction. As in other Caribbean localities, spawning occurred after the full moons of August and September. However, there was some evidence of a third spawning episode after the full moon of October, possibly associated with a delay in the occurrence of maximum sea-water temperatures in near-equatorial localities compared to higher latitudes. The probability of cross-fertilization in this species with a gonochoric breeding system and a broadcasting mode of reproduction is favored by its balanced sex ratio, its usually high within-reef zone abundance, and by localized and repeated spawning episodes, synchronized by lunar phase. Received: 19 April 1996 / Accepted: 24 September 1996     

Reproductive biology and ecology of a deep-demersal fish, alfonsino Beryx splendens, over the seamounts off New Caledonia

The reproductive biology of the alfonsino Beryx splendens was studied by histological examinations, gonadosomatic index and macroscopic scales of maturation of a large sample of gonads. Alfonsino is a gonochoric species. The size-frequency distribution of the sex ratio was bimodal and considered to be due to size dimorphism. In New Caledonia, the breeding period of this species occurs during the southern summer, with a peak in December to January. The spawning stage is attained at a minimum fork length of 28 cm for females and 33 cm for males. The size at which 50% of the population attain sexual maturity (FL₅₀) is 33.2 cm for females and 34.5 cm for males. Maximum potential fecundity is estimated to lie between 270 000 to 675 000 eggs for fish between 34 and 40 cm in fork length. It was possible to differentiate vegetative zones, in which juvenile alfonsino grow until they reach maturity, from reproductive zones (fishing grounds) which are inhabited by mature individuals. The larvae and juveniles could be carried from the reproductive zone to the vegetative zone by currents in an oceanic eddy system. Received: 26 April 1996 / Accepted: 20 September 1996     

Effect of diet on growth rate and reproductive fitness of Turbo sarmaticus (Mollusca: Vetigastropoda: Turbinidae)

Experiments were conducted to determine the effect of four algal diets (Corallina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture of these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12 months), reproductive fitness of mature specimens (gonad index up to 33%) and energy reserves (up to 4.76 mg glycogen/100 mg foot tissue) were achieved when T. sarmaticus was fed U. rigida or a mixed diet. In addition, the gonad index of individuals fed these diets was almost twice that of similar-sized field specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reproductive fitness of adults fed on such a diet was also poor (gonad index <4.5%) and energy reserves were low (<3.5 mg glycogen/100 mg foot tissue). Along the southeastern coast of South Africa, T. sarmaticus has a distinct reproductive cycle with gametogenesis occurring from March/April until August/September, whilst maturity (gonad index = 15%) was maintained until December, after which spawning occurred until March. Received: 6 July 1998 / Accepted: 8 March 1999     

Reef coral reproduction in the Abrolhos Reef Complex, Brazil: the endemic genus Mussismilia

The current contribution deals with the reproductive biology of a genus endemic to Brazil –Mussismilia Ortmann, 1890 – including all three species of the genus: M. braziliensis (Verrill, 1868), M. hartti (Verrill, 1868), and M. hispida (Verrill, 1902), which occur sympatrically in the studied area, the Abrolhos Reef Complex, Brazil. Sexuality patterns, modes of reproduction, synchrony and spawning periods are reported, and were determined by histological examination of material. All three species started to develop female and male gametes over different periods in the same breeding season. The three species are probably broadcast spawners, since no embryos or planulae were observed in any species at any given time of the year. Each reproductive cycle lasted approximately 11 months. Oogenesis and spermatogenesis started in different periods, with spermaries appearing in approximately the eighth month of ovary development and lasting about 3 months. Reproductive cycles were annual. Spawning probably occurred in consecutive months in each species. In M. braziliensis, spawning presumably happened between March and the middle of May in 1996 and 1997. Evidence suggested that spawning events of M. hispida took place between the end of April and mid-June. M. hartti may have spawned between September and November. The data presented here suggested that all studied species have at least one exclusive spawning period, asynchronically with the others. A possible exception may be the simultaneous (or close) spawnings of M. braziliensis and M. hispida in May. It is suggested that asynchrony in spawning periods among species may reduce the chance of hybridization, gamete waste and the competition for settlement surfaces. The occurrence of extended spawning periods for each species may also reduce the risks of reproductive failure, due to temporary adverse conditions. Received: 8 December 1998 / Accepted: 15 July 1999     

Reproductive dynamics of endeavour prawns, Metapenaeus endeavouri and M. ensis, in Albatross Bay, Gulf of Carpentaria, Australia

 The spawning patterns of two penaeid prawns, Metapenaeus endeavouri (Schmitt) and M. ensis (De Haan), were examined from data collected at 45 stations between March 1986 and March 1992. An index of population fecundity based on the abundance, proportion and fecundity of sexually mature females was used as a measure of spawning output of the prawn stock. The population fecundity index for M. ensis was higher than that for M. endeavouri. The monthly population fecundity index for M. endeavouri varied markedly among years, while that for M. ensis was consistent among years. Spawning of M. endeavouri occurred year-round, while that of M. ensis was concentrated mainly in spring (September to November). For M. endeavouri, a minor spawning, derived from a relatively small number of summer spawners, occurred in the 20 to 30 m offshore waters in summer. In early summer (after May), the major spawning group consisted of large females from the winter-spawning cohort, and the spawning area shifted to depths of 30 to 60 m. In winter (July), the major spawning, derived from the winter-spawning cohort, occurred at depths of 20 to 40 m. For M. ensis, the major spawning, derived from the spring-spawning cohort, was observed in depths <50 m and was concentrated particularly in inshore waters (<20 m) in spring. In autumn, the spawning output was mainly from the autumn-spawning cohort, which comprised but a small number of individuals. In winter, the major spawning group again consisted of the large females from the spring-spawning cohort, and spawning increased in the oceanic waters (>50 m). These results suggest that mature female M. endeavouri and M. ensis move offshore (>40 m) by May and July, respectively, and return to shallow waters (<35 m) in July and November, respectively. The monthly reproduction patterns of both species in the “effective spawning” area showed that the major spawning season for M. endeavouri is August to October and that for M. ensis is September to December. Received: 19 February 1999 / Accepted: 18 June 2000     

Size-dependent reproduction in the Caribbean gorgonian Pseudoplexaura porosa

Reproductive success among clonal taxa is often portrayed as a simple function of clone size, but reproduction in Pseudoplexaura porosa (Houtuyn), a common Caribbean gorgonian, reflects a more complex relationship between size and gamete production. Tagged colonies were sampled at two reefs in the San Blas Islands, Panama during the 1995 spawning season to determine the colony size at first reproduction, size-dependent polyp fecundities, and whole colony gonad production, and to follow the gametogenic cycle. Additional data were obtained during non-spawning months in 1984 and 1985. Of 120 colonies ranging in height from 20 to 250 cm, only colonies taller than 50 cm were reproductive. An average of 4.33 oocytes polyp⁻¹, 560 to 800 μm in diameter, were released during monthly synchronous spawning events from June to September. Oocytes released each month developed from a group of intermediate size oocytes present at the end of the preceding month. Almost all oocytes >560 μm were released during each spawning event. Spermatogenesis was a shorter process than oogenesis. During each spawning month, mature spermaries developed from a group of <125 μm spermaries. Virtually all spermaries >190 μm were released each month, and most of the spermary volume in mature male polyps was generated anew each month of spawning. Among reproductive colonies, polyp fecundity increased with colony height from 50 to 200 cm. Per capita fecundity of >200 cm tall female colonies was lower than for 150 to 200 cm colonies, but whole colony fecundity of large colonies was greater due to the exponential increase in the number of polyps that occurs with increasing colony height. In male colonies, both polyp and colony reproductive output increased with colony height. The large amounts of sperm produced by large male colonies probably contributes to the high rates of in situ fertilization observed in P. porosa. Differences in fecundity as a function of colony size and sex suggest differences in some combination of the cost of reproduction and/or allocation of resources to reproduction. Received: 9 September 1998 / Accepted: 7 June 1999     

Mass spawning by the sea urchin Evechinus chloroticus (Echinodermata: Echinoidea) in a New Zealand fiord

A mass synchronous spawning of the sea urchin Evechinus chloroticus (Valenciennes) was observed in situ in Doubtful Sound, a large New Zealand fiord. Spawning occurred between 17:30 hrs and 18:30 hrs on 27 January 1994 and coincided with a full moon, spring tides and a period of decreasing sea temperatures. During spawning, the sea urchins formed a dense spawning aggregation of both sexes, with >90% of the urchins observed spawning at the time. Spawned gametes clouded the water column, and some were eaten by small labrid fish species. The spawning, which may have been as widespread as 40 km, marked a 42 to 50% decrease in gonad indices and resulted in a widespread, dense cohort of  E. chloroticus larvae within the fiord. Received: 25 September 1997 / Accepted: 6 March 1998     

Introduction of the northern Pacific asteroid Asterias amurensis to Tasmania: reproduction and current distribution

The northern Pacific asteroid Asterias amurensis (Lütken) has been recently introduced to Tasmania and is now well-established in east and southeast Tasmania. This sea star is conspicuous throughout the Derwent River estuary and is particularly abundant in the Hobart port area. Reproduction of two populations of A. amurensis at Sullivans Cove and at Sandy Bay was investigated from August 1993 to October 1994 by gonadal histology and measurement of the gonad index (GI). An intense period of vitellogenic and spermatogenic growth started in April, with the breeding condition reached by June. In 1994, peak GI was recorded at Sullivans Cove in July and at Sandy Bay in August. Although these data indicated that the Sullivans Cove population spawned before the Sandy Bay population, histological examination revealed that major spawning activity occurred in both populations from July onwards. In the early part of the breeding season, gametogenesis proceeded in parallel with spawning, with released gametes being replaced by continual gametogenesis. Maintenance of a higher GI during the early part of the breeding season at Sandy Bay was due to prolonged gametogenic replacement at this site. Spawning continued to October 1994, resulting in a sharp decline in the GI. The cyclic expansion and regression of the genital haemal sinus coincident with germinal proliferation and growth, respectively, support the contention that haemal fluid provides nutrients for gametogenesis. In Tasmania, A. amurensis experiences temperature and photoperiod regimes similar to those experienced by endemic populations of this species in the north Pacific. Comparison of reproduction of A. amurensis in Japan and Tasmania at similar latitudes shows that gametogenesis of the northern and southern populations is 6 mo out of phase. This phase shift provides evidence for photoperiodic regulation of gametogenesis in A. amurensis. The similar trend in sea-temperature regimes associated with the stages of gametogenesis in northern and southern populations suggests that temperature also plays a modulatory role. Based on the periodicity of reproduction and the ontogeny of A. amurensis, the planktotrophic larvae of this species would be expected to be in the plankton for several months from the end of winter through summer. Considering the highly fecund, dispersive life-history of A. amurensis, the southeast Tasmanian populations have considerable potential to serve as a seed source for establishment of new populations of this asteroid elsewhere in Tasmania and in mainland Australia. Received: 18 October 1996 / Accepted: 22 October 1996     

Reproductive biology of the antipatharian black coral Antipathes fiordensis in Doubtful Sound, Fiordland, New Zealand

The reproductive biology of Antipathes fiordensis Grange, a species endemic to south-western New Zealand, was followed from April 1994 to May 1995. Ten colonies were individually tagged in Doubtful Sound and sampled on a monthly basis in order to determine their reproductive activity. The fecundity of each of the five tagged female colonies was determined by estimating the total number of polyps per colony from photographs of each colony and by planimetry, the proportion of gravid polyps per colony, and the mean number of oocytes per gravid polyp. In addition, 56 colonies were sampled in March 1995 to estimate the sex ratio, height at sexual maturity, and mean sizes of females and males. A. fiordensis was found to be a dioecious species which, in the absence of gonads in the polyps, has no obvious external morphological differences between the sexes. Broadcast spawning of gametes is the likely mode of reproduction. Gametogenesis began in November 1994 and was highly synchronous within and between colonies, with spawning occurring in March 1995. The sex ratio in adults was 1:1. Colonies reached sexual maturity between the heights of 70 and 105 cm which, based on existing estimates of growth rate, corresponds to a minimum age for sexual maturity of about 31 yr. The largest oocytes measured ranged from 100 to 140 μm in size. Female colonies produced between 1.3 and 16.9 million oocytes, with the larger colonies dominating the reproductive output of the population. Received: 23 June 1997 / Accepted: 1 August 1997     

Interannual, seasonal, local and body size variations in reproduction of the prawn Penaeus (Marsupenaeus) japonicus (Crustacea: Decapoda: Penaeidae) in the Ariake Sea and Tachibana Bay, Japan

 The reproductive biology of female Penaeus japonicus Bate was investigated in the Ariake Sea and Tachibana Bay (located outside the Ariake Sea), Japan from 1994 to 1996. Interannual, seasonal, individual female body size and spatial influences on the incidence of spawning were examined. The proportion of inseminated females, increased with increasing body size up to 170 mm body length (BL) and decreased thereafter. The minimum size at maturity was similar between years; 130 to 140 mm BL. The minimum size of individuals with developing ovaries or spermatophores differed from that of ripe females by 20 to 25 mm. Spawning occurred in the central part of the Ariake Sea and Tachibana Bay but rarely in the inner part. P. japonicus had a clear reproductive cycle. Spawning started earlier and ended later, occurring from mid-May to mid-October, in the eastern central part of and outside of the Ariake Sea compared with the western central part, where spawning occurred from mid-June to mid-September. Spawning dynamics differed across seasons, body sizes and areas but not across years. The seasonal peak in the proportion of ripe females varied with body size. In small individuals (130 to 169 mm BL), no peak was observed, whereas in large individuals (>170 mm BL) the proportion of ripe individuals peaked in June. The proportion of ripe individuals increased with increasing body size and was high outside the Ariake Sea. Factors causing the variation in spawning dynamics are discussed. Received: 30 November 1998 / Accepted: 12 October 1999     

Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina

The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes, well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion. Received: 21 June 1999 / Accepted: 25 January 2000     

Reproductive variability over a four-year period in the sea urchin Evechinus chloroticus (Echinoidea: Echinodermata) from differing habitats in New Zealand

 The endemic New Zealand echinoid, Evechinus chloroticus (Valenciennes), was sampled approximately monthly from September 1990 to October 1994 at three sites in Tory Channel, Marlborough Sounds, New Zealand. These channel sites (outer, mid and inner) were up to 20 km from the open ocean and differed in their shore type, exposure to wave action and macrophyte abundance. E. chloroticus showed an annual reproductive cycle at each site, with gametogenesis commencing in the late austral winter and spawning in summer. Maximum gonad indices (reproductive potential) varied spatially, with the outer site generally having higher maximum gonad indices than the inner site, and temporally, with maximum gonad indices occurring earlier in 3 of the 4 seasons at the outer site than the inner site. The mid and inner sites showed much greater variation in maximum gonad indices (range 15.83 to 26.99% and 11.87 to 20.90%, respectively) than the outer site (range 19.31 to 22.95%). Reproductive output (weight of gametes released per gram echinoid) also varied, with the different sites showing significantly different outputs in the different years. A regression of maximum reproductive potential against reproductive output was significant ( p < 0.001), and had a positive slope with an r ² of 0.79. While, the initiation of gametogenesis was relatively synchronous between sites and years, and is possibly cued by increasing daylength, it progressed at different rates among populations. Spawning did show spatial and temporal variability, occurring near the time of highest sea-surface temperatures (∼15 °C). The observed variations in reproductive cycle may be related to small-scale variability in diet and environmental conditions. Furthermore, asynchronous spawning, variable spawning duration, and variable reproductive output are likely to strongly influence annual recruitment variability in E. chloroticus, with different larval subpopulations contributing unequally in different years. The ecological consequences of this, both for the ability of E. chloroticus to propagate itself in space and time and for the management of the developing E. chloroticus fishery in New Zealand, are discussed. Received: 9 December 1998 / Accepted: 13 June 2000     

Social organization and sexual pattern in the Mediterranean parrotfish Sparisoma cretense (Teleostei: Scaridae)

We examined the social organization and reproductive pattern of a population of Sparisoma cretense L. at Lampedusa Island (Italy). During the breeding season (July to September) individuals occur either in territorial or in non-territorial groups, which quantitatively differ with respect to use of space, sex-ratio and sexual activity. Territorial groups consist of one male plus one to three females, whereas in non-territorial groups as many as 54 fish share a common area. Among non-territorial groups, variations, in both sex-ratio and behavior, suggest they could represent either feeding aggregations or reproductive aggregations. Spawning, always in pairs, occurs daily in a short period of time before dusk and has been observed only in territorial groups. Group spawning has never been observed, but another alternative mating tactic, streaking on pair spawning, was recorded. In the non-breeding season fish do not aggregate in organized social units. Histological examination of gonads showed that adults are larger than 12 cm total length. Females have an asynchronous ovary, typical of species spawning several times during the breeding season. Males show secondary testes, indicating that their gonads develop ovaries as juveniles, which are later redifferentiated into functional testes. Histological and demographic data seem to indicate that, as in other species of this genus, prematurational sex-change occurs. The sexual pattern appears to be essentially gonochoristic, but the potential for sex-change is not excluded. Received: 5 January 1999 / Accepted: 22 June 1999     

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location. Received: 10 December 1996 / Accepted: 16 January 1997     

Between-area differences in age and length at first maturity of the orange roughy Hoplostethus atlanticus

Mean age and length at onset of maturity were estimated for orange roughy (Hoplostethus atlanticus) populations off New Zealand, Namibia, and Great Britain. Significant between-area differences were apparent in both these parameters. Implications of the between-area differences on stock structure of orange roughy in New Zealand waters are discussed. A proportional relationship between age at onset of maturity and modal size of fish in the mature population is demonstrated. This is consistent with later-maturing fish experiencing a longer period at a pre-maturity growth rate that is relatively faster than the rate of somatic growth after maturity. Received: 22 December 1997 / Accepted: 5 May 1998     

Distribution pattern, reproductive biology, and fishery of the wedge sole Dicologlossa cuneata in the Gulf of Cadiz, south-west Spain

The wedge sole Dicologlossa cuneata (Moreau, 1881) is a coastal species that lives along the inner shelf waters of the Gulf of Cadiz down to a depth of 115 m. Its fishery, the size composition of the exploited population, and its reproduction have been studied on the basis of data acquired from commercial statistics from 1984 to 1994 and from sampling carried out during 1993 and 1994. The relative abundance of the species and its geographic and bathymetric distribution have been examined by analysis of four trawl surveys carried out from 1992 to 1994. D. cuneata is captured mainly by the trawl fleet, and to a lesser extent by gillnet gears. Wedge sole fishery has a marked seasonality. Size-frequency distributions from commercial samples and from bottom-trawl surveys are very similar, ranging from 12 to 26 cm total body length (TL). D. cuneata is a “repeat-spawner”. Peak spawning is from January to May. Females attain sexual maturity at 18 cm TL, while sexually mature males have been observed at 15 cm TL. The flexibility of the spawning strategy of D. cuneata throughout its distribution range is discussed. The scarcity of small specimens in the monthly samples and sequential spawning throughout the year prevented the estimation of growth parameters by means of length-frequency analysis. D. cuneata is present in greatest abundances in the sandy–muddy bottoms of the Guadalquivir River mouth at 15 to 30 m depth. Its optimum habitat coincides with the principal commercial fishing grounds. The possibility of reproductive vertical migration is discussed, but more precise data are needed before a viable hypothesis can be made. Received: 1 July 1997 / Accepted: 27 November 1997     

Egg production of Calanus finmarchicus : effect of temperature, food and season

The use of the egg production rate of herbivorous copepods as an important parameter for understanding population dynamics and as an index of secondary production requires knowledge of the regulatory mechanisms involved and of the response to changes in food concentrations and temperature. Furthermore, the effects of season and generation on egg production have to be studied. In this context data are presented for Calanus finmarchicus from the northern North Atlantic. Prefed and prestarved females were exposed to different concentrations of the diatom Thalassiosira antarctica over 1 to 2 wk at 0 or 5 °C, and egg deposition was controlled daily. Egg production increased with higher food concentrations, but much less when prestarved. The effect of temperatures between −1.5 and 8 °C on egg production was studied in females maintained at optimum feeding conditions. Egg production rate increased exponentially over the whole temperature range by a factor of 5.2, from 14.2 to 73.4 eggs female⁻¹ d⁻¹, and carbon-specific egg production by 4, from 2.1 to 8.5% body C d⁻¹. The response to starvation was also temperature dependent. In both the temperature and feeding experiments egg production rate was regulated mainly by changes of the spawning interval, while changes of clutch size were independent of experimental conditions. Different responses to optimum feeding conditions were observed in females collected in monthly intervals on three occasions between March and May. The March females deposited more clutches than the April and May females. In May, >50% of the females did not spawn at all. Maximum egg production rates were never >25% of the rate expected at 5 °C, indicating endogenous control of egg production in addition to food and temperature effects. Received: 4 August 1996 / Accepted: 11 September 1996