Evaluation of Atlantic bluefin tuna reproductive potential in the western Mediterranean Sea

Ovarian tissue samples of Atlantic bluefin tuna (ABFT) spawners (n = 49) caught by purse seine in the Balearic Sea (western Mediterranean) were used to assess the stock reproductive characteristics. The frequency of spawning females estimated by the postovulatory follicle method was 84% and the spawning periodicity 1.2 days. Using an unbiased stereological method, the realized batch fecundity was estimated from counts of postovulatory follicles (POFs), whereas the batch fecundity of the subsequent spawn was estimated by quantification of the number of follicles containing oocytes at maturation stage (OMFs). The number of POFs was used as a reliable proxy of the realized batch fecundity, as it represents the actual number of eggs released in the last spawning event. The average relative realized batch fecundity was estimated to be approximately 48 eggs g^− 1 of total body mass. While the absolute batch fecundity was isometrically related to the fork length, the relative batch fecundity was not dependent on fish size, which leads to the assumption that all length classes contribute proportionally to their size, towards the total number of eggs spawned by the broodstock. Size-related variations in the sex ratio were observed in the study area and in other Mediterranean locations; females were more abundant in mid-size classes while males predominated in large-size classes.     

阿根廷滑柔鱼(Illex argentinus)雌性成熟个体的有效繁殖力及有效生殖投入

为掌握阿根廷滑柔鱼繁殖特性,根据2021年在西南大西洋公海采集到的阿根廷滑柔鱼样本进行计数和分析雌性成熟个体有效繁殖力,并利用能量密度测定技术测定分析其有效生殖投入。结果显示,阿根廷滑柔鱼雌性成熟个体的平均胴长为(244.90±16.36) mm,平均体质量为(295.16±64.85) g。雌性成熟个体的有效繁殖力为24 363～102 633粒卵母细胞,平均有效繁殖力为(63 158.49±16 782.00)粒卵母细胞;卵子能量密度值为25.01～26.09kJ/g,平均值为(25.71±0.25)k J/g;有效生殖投入为219.80～817.06 kJ,平均有效生殖投入为(465.02±158.71)kJ。在功能性成熟期,雌性个体的有效繁殖力和有效生殖投入均达到最大值。然而,自成熟度Ⅳ期至Ⅵ期,卵子能量密度值、体质量相对有效繁殖力、体质量相对有效生殖投入均没有显著差异。同时,混合模型结果显示,雌性成熟个体的有效繁殖力和有效生殖投入均随着体质量增加显著增大,但与个体体征没有显著相关性。结果表明,阿根廷滑柔鱼雌性成熟个体的有效繁殖力和有效生殖投入均与成熟体型大小密切相关,然而不同...     

Reproductive cycle,size at first maturation and fecundity in the golden ling,Genypterus blacodes,in Chile

Reproductive aspects of the golden ling, Genypterus blacodes, from the southern Chilean fishery are presented. Gonad samples were obtained from commercially caught fish between September 1999 and October 2000. Stage of sexual maturity, gonadosomatic index (GSI), and size of females at 50% maturation determined by logistic methods and by plotting the mean GSI by total length, are presented for both years. Batch fecundity was calculated from subsampling mature ovaries containing oocytes in advanced stages of maturity. Changes in GSI and monthly diameters of oocytes showed that ling had a spawning season which extended between August and November. The sizes at first maturity in 1999 and 2000 were 86.6 and 84.8 cm total length (TL), respectively, using the logistic model, and 84 cm for both years using the mean GSI‐size plotting method. The mean batch fecundity was 333 330 oocytes per individual for fish sized 85–120 cm TL. Fecundity increased with increasing weight and total length.     

Reproductive resilience of ice‐dependent Antarctic silverfish in a rapidly changing system along the Western Antarctic Peninsula

The Western Antarctic Peninsula (wAP) is globally one of the systems most heavily impacted by climate change, notably steep declines in sea ice extent. In forage species, reproductive resilience to change is particularly important because population fluctuations are rapidly communicated through the system via trophic interactions. The reproductive traits of the ice‐dependent forage species Antarctic silverfish (Pleuragramma antarctica) from different areas along the wAP and at the tip of the Antarctic Peninsula were investigated through macroscopic and histological analyses of gonads, with the aim to assess its reproductive potential and to test for spatial differences in fecundity and spawning season. Fish samples were collected in late summer off Charcot Island, in Marguerite Bay and off Joinville Island; no fish were caught in the central wAP. Samples from Charcot Island and Marguerite Bay consisted of adults in developing gonad stage, whereas those from Joinville consisted almost exclusively of juveniles. Mean GSI was relatively low (2–3%) and similar in both sexes, as specimens were still far from being actively reproducing. Developing females exhibited two discrete, though partially overlapping modes of oocytes of different size, with vitellogenic oocytes measuring 0.5–1.0 mm. Absolute and relative fecundity ranged between 3000 and 12,000 eggs per female and between 80 and 190 eggs·g^?1, with a strong relationship between absolute fecundity and body size. These results were consistent with a single population at Charcot Island and Marguerite Bay and indicated substantial reproductive potential, which may mitigate population isolation and reductions in habitat availability but cannot ultimately offset catastrophic loss of spawning habitat linked to sea‐ice retreat.     

Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be a determinate spawner, maturing all eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs per female left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185–300 mm prosomal width, with by far the highest concentration in the mid‐size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid‐size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid‐size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size‐selective harvest, reproductive value, and stable stage distribution of populations.     

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

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

The impact of musk ketone on reproduction in zebrafish (Danio rerio)

Nitro musks are a group of nitrated benzenes mainly used by the fragrance industry as a substitute for natural musk. Two of the most common nitro musks, musk xylene and musk ketone, have been detected in water, fish, human adipose tissue, as well as in human breast milk. In this study, female zebrafish were dietary-exposed to musk ketone, prior to spawning with unexposed males. The fish were exposed for 8 weeks at two different dose levels. Accumulation of the compound in the fish as well as reproductive success were studied. Exposed females had reduced body weight and length, as well as reduced liver- and gonad somatic index. The results from the reproduction study showed a dose-dependent reduction in fecundity. Early life-stage mortality was increased and the median survival time was reduced. In addition, an embryo/larvae toxicity test was performed, using newly fertilized zebrafish eggs from unexposed parental fish. Eggs were exposed to a series of different concentrations of musk ketone via the surrounding water. A NOEC value of 10 μg/l and a LOEC value of 33 μg/l was determined. Conclusively, the present study clearly shows that musk ketone negatively affects reproduction and early life-stage survival in zebrafish.     

The reproductive biology of a shallow water morid (Salilota australis Günther, 1878), around the Falkland Islands

The reproductive biology of a shelf morid, red cod (Salilota australis) was investigated in the Falkland Islands, in order to expand our knowledge of the reproductive strategy of this relatively unstudied family of fishes. Red cod spawn to the south and south-west of West Falkland between August and October. Length frequency and sex ratio data suggest that females arrive at the spawning grounds first. The greatest spawning activity occurred in early evening and this timing may be an adaptation to reduce predation on eggs. Ripe egg size varied from 0.95 to 1.26 mm and was not dependant on female size. There was no regulative atresia during maturation and the formation of fecundity and fecundity increased with increasing fish total length (L_T) from 300,000 (42-45 cm L_T) to 4.5-9.0 million eggs (75-83 cm L_T). The fecundity of most of the population was between 2 and 5 million eggs. Red cod releases small batches of eggs over the spawning period. Batch size ranged from 30,000-90,000 (39-42 cm L_T) in smaller animals to 400,000-800,000 (>75 cm L_T) in larger animals and the batch size of first spawners was significantly higher than for advanced spawners. The study allows us to discuss the evolutionary relationships between the Gadiformes.     

DDT in trout and its possible effect on reproductive potential

Eggs of rainbow trout (Salmo gairdneri Richardson) from five different lakes in North Island, New Zealand, were reared to discover whether they showed significant differences in survival which could be linked with DDT levels in the tissue. The muscle and gonads of pre‐breeding season fish and the parent females were assayed for DDT, as were the whole fry at the end of rearing. The highest DDT levels were found in fish from Lake Rerewhakaaitu, and eggs from these fish showed the least viability. Mortality was relatively low among eggs from fish out of the other lakes. Thus, DDT may possibly contribute to the high mortality found in eggs from Lake Rerewhakaaitu fish.     

Life history strategies in zooplankton communities: The significance of female gonad morphology and maturation types for the reproductive biology of marine calanoid copepods

The present review addresses the reproductive strategies of marine calanoid copepods, as affected by their physiological preconditioning, and aims to enhance understanding of their adaptations to specific environmental conditions.Knowledge about oocyte development and internal gonad structure, especially in relation to feeding conditions, is essential for a complete understanding of the reproductive strategies of the copepods. Therefore, the foci of the review are to identify general patterns in oocyte and gonad development in calanoid copepod species from marine ecosystems worldwide and to elucidate the significance of gonad structures for reproductive strategies.Oogenesis is similar in all copepod species. During maturation, the morphology of the oocytes changes distinctly and, according to oocyte size and appearance of ooplasm and nucleus, five oocyte developmental stages are distinguished. In contrast, the gonad structure and its changes during the spawning cycle differ considerably among species, and these differences are related to specific reproductive traits.Four gonad morphology types can be distinguished: the Calanus-type, found in species from all over the world with distinctly different life history traits, is apparently most common in calanoid copepods. In this gonad type, most oocyte developmental stages are present simultaneously, and usually many oocytes mature synchronously, all of which are released in one clutch. The gonad structure allows frequent spawning and large clutches, hence, high egg production rates. This may be a preconditioning for exploiting seasonally high food supply. However, the Calanus-type was also found in species producing eggs at lower rates. In the diverticula of Pseudocalanus-type gonads, only two oocyte developmental stages are present and usually fewer oocytes mature synchronously. Accordingly, the egg production rate is generally lower as compared to the Calanus-type, and apparently only this gonad-type is structurally suitable for ovigerity. Species with Pseudocalanus-type gonads are present from polar seas to the tropics, some of them being key species. The Acartia-type was scarce, found in only one species, Acartia clausi. Here all oocyte developmental stages are present, including intermediate stages, but only a few oocytes mature synchronously and are released together. High spawning frequency compensates for the small clutches, and hence egg production rate may be as high as in Calanus-type gonads. In the Aetidius-type gonad, the total number of oocytes in the diverticula is low as is the number of oocytes maturing synchronously. Less is known about the reproductive biology of species with Aetidius-type gonads; however, their distribution and feeding patterns suggest that this type is common in species inhabiting environments of low food availability.The differences in gonad structures also lead to differences in the egg size:female size ratio, as the space available for each mature oocyte depends on the total number of oocytes. Independent from gonad-type, the eggs are relatively large in species in which the gonads contain only few oocytes, whereas small eggs are produced by species with gonads filled with many oocytes. Since all species carrying their eggs in external sacs until hatching (ovigerous species) have Pseudocalanus-type gonads, the scatter in their egg size:female size ratio is low. The broadcast spawning species are of all gonad-types, and consequently the scatter among them is high.A major factor affecting the timing and magnitude of spawning of calanoid copepods is the energy supply for gonad development. Therefore, part of the review elucidates the role of internal and external resources in fuelling egg production. In many species, freshly assimilated food is transferred into egg material within a short period of time, and clutch size and spawning frequency are the two parameters that allow adjustment of egg production to food availability and temperature. However, internal body reserves may also fuel oocyte development. The extent to which oogenesis depends on ambient feeding conditions varies considerably among species and even within species, apparently reflecting their adaptation to specific environmental conditions. All copepod species continue to release eggs for a short period after the onset of starvation, indicating that a short-term nutrient pool fuels final oocyte maturation. Some species, especially from polar and subpolar regions, are capable of reproducing on internal reserves, either solely or in addition to freshly ingested food, hence, decoupling the reproduction to some extent from the spring bloom. The reproductive strategy of Calanus finmarchicus, which responds with extreme flexibility to variations in food supply, is presented here as an example for the complexity of the reproductive processes in a calanoid copepod.In accordance with their physiological pre-conditioning, the calanoid copepod species exhibit distinctly different reproductive patterns. Polar and sub-polar environments are characterized by strong seasonality in light regime, and hence, phytoplankton concentration. The reproductive activity of many dominant (herbivorous) species peaks during the spring bloom. However, species that utilize internal reserves or food resources other than phytoplankton, reproduce before and after the bloom, or even year-round. In the North Atlantic, presented here as an example for a boreal marine ecosystem, maximum reproduction of the dominant copepod species Calanus finmarchicus occurs during the spring bloom. However, the timing of peak spawning varies between areas, as the onset of the bloom varies with hydrography and climate. The subtropical Gulf of Aqaba, in contrast to other subtropical systems, is characterized by seasonal phytoplankton succession driven by thermal winter convection. These changing environmental conditions, however, did not affect the reproduction of two of the dominant species, Clausocalanus farrani and C. furcatus. In contrast, other calanoid species exhibit reproductive cycles, either related to temperature (Ctenocalanus vanus) or to ontogenetic migration (Rhincalanus nasutus).The information gained from studies of morphology and reproductive traits contributes to standardization of methods in reproductive studies. Based on detailed knowledge of gonad morphology and its changes during maturation and due to food supply, classification schemata have been developed allowing the identification of females ready to spawn. In a next step, egg production may be estimated from preserved females by assessing clutch size through the number of maturing oocytes in the gonads. This approach, however, is as yet applicable only to the species best studied, Calanus finmarchicus.The present review shows that morphological studies on gonad maturation processes may provide significant contributions to fundamental ecological questions. Thus, they extend our knowledge of reproductive ecology from simply relating reproductive traits to abiotic and biotic factors toward a mechanistic understanding of how reproduction is regulated in calanoid copepods.     

Reproductive and growth strategies of Idotea balthica basteri (Pallas, 1772) population in the Bizerte lagoon (Tunisia,Southern Mediterranean)

We analysed several life history traits of the marine isopod Idotea balthica basteri (Pallas, 1772) from the Bizerte lagoon, Southern Mediterranean Sea. Growth was continuous throughout the life of the animal with a high growth rate in the first life phase, and the growth curve was described according to von Bertalanffy's model. The lowest growth rate (0.23 mm) was recorded in winter (December, January and February) and the maximum rate (2.31 mm) between April and June. The total number of hatched eggs or embryos was positively correlated with the body length of ovigerous females. This population of I. balthica basteri was iteroparous, showing distinct strategies of reproduction. Large ovigerous females with high fecundity were collected during the whole sampling period, while breeding in smaller females with low fecundity was restricted to the period from late spring to early autumn, Manca size increased significantly with increasing female body size and there was also a significant trade‐off between manca size and the number of eggs per brood. Reproductive allocation, ranging between 17.1 ± 1.2% in winter and 23.2 ± 1.8% in summer, was positively correlated with female weight. Accordingly, parental investment in producing a juvenile varied between 1.02% per manca in winter to 3.38% in spring. Evaluated traits show that late summer and autumn cohorts have a K‐strategy, whereas cohorts born in winter and spring, and which exhibit a shorter life time, exhibit faster development, earlier reproduction and a smaller parental investment tending towards an r‐selected strategy.     

Protracted oogenesis and annual reproductive periodicity in the deep‐sea pennatulacean Halipteris finmarchica (Anthozoa,Octocorallia)

Halipteris finmarchica is one of the most common species of deep‐sea pennatulacean corals in the Northwest Atlantic; it was recently determined to act as a biogenic substrate for other species and as a nursery for fish larvae. Its reproductive cycle was investigated in colonies sampled in 2006 and 2007 along the continental slope of Newfoundland and Labrador (Canada). Halipteris finmarchica exhibits large oocytes (maximum diameter of 1000 μm), which are consistent with lecithotrophic larval development. Female potential fecundity based on mature oocytes just before spawning was ~6 oocytes · polyp^?1 (500–6300 oocytes · colony^?1); male potential fecundity was 16 spermatocysts · polyp^?1 (5500–57,400 spermatocysts · colony^?1). Based on statistical analysis of size‐probability frequency distributions, males harboured one cohort of spermatocysts that matured inside 8–11 months, whereas females harboured two distinct cohorts of oocytes; a persistent pool of small ones (≤400 μm) and a small number (~20%) of larger ones that grew from ~400 to >800 μm over a year. Despite this difference in the tempo of oogenesis and spermatogenesis, a synchronic annual spawning was detected. A latitudinal shift in the spawning period occurred from south (April in the Laurentian Channel) to north (May in Grand Banks and July–August in Labrador/Lower Arctic), following the development of the phytoplankton bloom (i.e. sinking of phytodetritus). Prolonged oogenesis with the simultaneous presence of different oocyte classes in a given polyp is likely not uncommon in deep‐sea octocorals and could hamper the detection of annual/seasonal reproduction when sample sizes are low and/or time series discontinued or brief.     

Egg production of turbot,Scophthalmus maximus,in the Baltic Sea

In the brackish water Baltic Sea turbot spawn at ~ 6–9 psu along the coast and on offshore banks in ICES SD 24–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05 ± 0.03 mm diameter and 46.8 ± 6.5 μg dry weight; mean ± sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish.     

Metridia pacifica in Dabob Bay, Washington: The diatom effect and the discrepancy between high abundance and low egg production rates

Information on life cycle strategies and reproductive parameters of Metridia pacifica is scarce, despite its importance in the zooplankton of the subarctic Pacific. In many regions it occurs in high abundance, but reproductive rates, when reported, are usually low. This discrepancy was studied in Dabob Bay, Washington, USA, in the context of an investigation of the effect of diatom blooms on the reproductive success of copepod grazers.In situ egg production rates of M. pacifica were measured in spring and mid-summer with standard methods (multi-wells) and a new incubation chamber (spawning towers) that separates the spawning female from its eggs and allows the eggs to develop undisturbed. Many females did not produce eggs, possibly due to a high fraction of immature individuals. Egg production rates were variable, but clutch sizes were higher in spawning towers, and estimates of female egg cannibalism revealed that females consume many eggs shortly after their release. Thus, a separation of females and eggs is mandatory for accurate measurements of M. pacifica egg production rates. The maximum clutch sizes recorded in our study were comparable to measurements for other calanoids. However, unviable eggs were a large fraction of those spawned, independent of incubation method, especially in late winter and early spring. In order to assess whether the diatom effect may be responsible for low viability of embryos and nauplii, we also measured in situ grazing. Adult females were omnivorous, but they ingested some diatoms that rank among the strongest anti-mitotic toxin producers known so far. Although M. pacifica’s vertical migration behavior suggests opportunistic feeding on abundant food during their short stay in the phytoplankton-rich surface, they often ignored the food items that contributed most to microplankton carbon concentrations. Thus, their feeding strategy remains ambiguous. Due to severe reproductive failure early in the season, recruitment was impaired in spring, while the population increased, reaching high abundance in mid-summer when reproductive output was low. While advection and interannual variability in bloom conditions might compensate for the losses described here, the paradox of high Metridia abundance versus low reproductive success still requires further investigation, and methodological constraints need to be ruled out in future studies.     

Fecundity of chinook salmon (Oncorhynchus tshawytscha) from the Waitaki and Rakaia Rivers,New Zealand

The fecundity of chinook salmon (Oncorhynchus tshawytscha) was estimated from maturing fish captured by anglers in the lower Waitaki River in 1985 and 1987–89, and from mature fish spawned at the Glenariffe Research Station on the Rakaia River in 1992. Fecundity was positively correlated with fork length (FL); estimated fecundities at 750 mm FL were 5024 eggs for Waitaki and 4829 eggs for Glenariffe salmon. The slopes of the regressions of fecundity on FL differed between the populations but the Glenariffe data did not differ from Rakaia River samples from 1967, 1973, and 1976. Significant inter‐annual variation in the FL‐fecundity relationship was detected in Waitaki River samples. Egg weights, taken from the Glenariffe samples, were positively correlated with length and averaged 0.17 g. However, salmon with high fecundity for their FL tended to have small eggs, and vice versa.     

Rapid shipboard identification and enumeration of pelagic marine fish eggs by a simple photographic technique (note)

A technique is described for obtaining rapid high‐quality silhouette photographs of plankton samples at sea. This technique was designed to facilitate identification and enumeration of pelagic marine fish eggs in near real‐time. It uses readily available photographic materials and unlike previously described techniques, the silhouettes are recorded directly on to photographic paper rather than film. The resolution is adequate for microscopic measurements. Examples are presented from a cruise off Westland, New Zealand, which investigated the distribution of hoki eggs.     

Fecundity in the marine spiny lobster Jasus verreauxi (H. Milne Edwards) (Crustacea: Decapoda: Palinuridae)

Fecundity in Jasus verreauxi (H. Milne Edwards, 1851) has been studied by a detailed investigation of (a) the total weight of eggs carried by female specimens, (b) the average number of eggs per 1 g sample, and (c) the total number of eggs carried by females. In mid October 1966, 217 females “in berry” (that is, carrying external eggs) were examined and measured at Spirits Bay, New Zealand. The fecundity study is based on the results obtained from 21 selected specimens, with carapace lengths from 15.5 cm to 23.5 cm.

A direct relation was found between the total weight of eggs carried and increase in carapace length. The total weight of eggs carried varied from about 51 g to 238 g for carapace lengths of 15.5 cm to 23.5 cm. No correlation was shown between the average number of eggs per 1 g sample and increase in carapace length. Considerable variation was noted in the number of eggs per 1 g sample, which ranged from a low count of 6,453 eggs to a high count of 8,341 eggs. The total number of eggs carried by female J. verreauxi was found to be related to an increase in carapace length. Furthermore, increase in fecundity per relative carapace length increase was noted to be greater in smaller specimens than in larger specimens. The total number of eggs carried ranged from about 385,000 for a carapace length of 15.5 cm to 1,940,000 for a carapace length of 23.5 cm.

Fecundity, as measured by the total weight of eggs carried and the total number of eggs produced, was found to be much higher in J. verreauxi than in several Jasus species previously studied by other workers.     

Biology of the redspotted tonguesole Cynoglossus zanzibarensis (Pleuronectiformes: Cynoglossidae) on the Agulhas Bank,South Africa

The biology of the redspotted tonguesole Cynoglossus zanzibarensis, a common African cynoglossid inhabiting the Agulhas Bank, South Africa, is described. Growth studies based on sectioned sagittal otoliths revealed that C. zanzibarensis is relatively fast-growing and long-lived, attaining ages >8 years. Growth in length was rapid in immature fish, fish attaining 56% of their maximum size within their first year. By sexual maturity, fish had attained 28% of their maximum age and 68% of their maximum length. Total length-at-age was best described by the Von Bertalanffy growth model with combined-sex growth described as L_t = 354.78(1?e^{?0.43 (t+1.17)}) mm TL. Sexually dimorphic growth patterns were evident, females attaining larger lengths, but at a slower growth rate than males. Despite the similar mean size of adult fish, the trawl-sampled adult population was dominated by females, with a sex ratio of 1 male:2.4 females. Female C. zanzibarensis mature in their second year of life (275 mm TL), after which they spawn small, pelagic eggs throughout the year. Approximations of the rates of total, natural and fishing mortality were estimated to be 0.62, 0.48 and 0.14 year^?1 respectively.     

The impact of musk ketone on reproduction in zebrafish (Danio rerio).

Nitro musks are a group of nitrated benzenes mainly used by the fragrance industry as a substitute for natural musk. Two of the most common nitro musks, musk xylene and musk ketone, have been detected in water, fish, human adipose tissue, as well as in human breast milk. In this study, female zebrafish were dietary-exposed to musk ketone, prior to spawning with unexposed males. The fish were exposed for 8 weeks at two different dose levels. Accumulation of the compound in the fish as well as reproductive success were studied. Exposed females had reduced body weight and length, as well as reduced liver- and gonad somatic index. The results from the reproduction study showed a dose-dependent reduction in fecundity. Early life-stage mortality was increased and the median survival time was reduced. In addition, an embryo/larvae toxicity test was performed, using newly fertilized zebrafish eggs from unexposed parental fish. Eggs were exposed to a series of different concentrations of musk ketone via the surrounding water. A NOEC value of 10 micrograms/l and a LOEC value of 33 micrograms/l was determined. Conclusively, the present study clearly shows that musk ketone negatively affects reproduction and early life-stage survival in zebrafish.     

渤海小黄鱼生殖力及其变化

根据2004年5月在渤海进行的拖网调查资料,分析了小黄鱼(Pseudosciaenapolyatics)在经过近半世纪的捕捞后的生殖群体生殖力及其与体长、纯体质量的关系,并对小黄鱼生殖力的变化作了比较。结果表明,小黄鱼的个体绝对生殖力为14729粒±1360粒;个体绝对生殖力与叉长、纯体质量的关系变化较大;与1964年历史资料相比,相同体长组小黄鱼的个体绝对生殖力F和相对生殖力FL都显著增大(P<0.01)。小黄鱼的生殖力增加可能是小黄鱼在长期捕捞等外部环境影响下的遗传进化以及对其生存环境的适应性响应。