Timing and size of blooms of the ctenophore Mnemiopsis leidyi in relation to temperature in Narragansett Bay, RI

The ctenophore Mnemiopsis leidyi is at the northern extreme of its geographic range in Narragansett Bay, an estuary on the northeast coast of the United States. Blooms have typically been observed in late summer and fall according to records from 1950 to 1979. We document an expansion of the seasonal range of this important planktonic predator to include springtime blooms during the 1980s and 1990s. This shift to an earlier seasonal maximum is associated with increasing water temperature in Narragansett Bay. Temperatures in spring have risen, on average, 2 °C from 1950 to 1999 with warm years being associated with the positive phase of the North Atlantic Oscillation. During 1999, M. leidyi appeared earlier in spring and was more abundant than during any previous year for which records are available. Changes in the seasonal pattern and abundance of this predator are likely to have important effects on planktonic ecosystem dynamics of Narragansett Bay. These include reduction of zooplankton abundance in spring followed by increases in size and frequency of summer phytoplankton blooms. Earlier blooms of M. leidyi may also reduce survival of eggs and larvae of fish because, as in 1999, they coincide with the period of peak spawning.     

The effect of extreme northerly climatic conditions on the life history of the minnow, Phoxinus phoxinus (L.)

Over its exceptionally wide geographical range the minnow displays a remarkable variability in its life history. In southern England many fish mature after one year and few fish survive to their third birthday. Very few fish spawned for more than one season but a 65-mm female is estimated to spawn up to 3172 eggs over the extended spawning season. In the River Utsjoki in Finnish Lapland maturity was strongly size-dependent and delayed until the fish reached 5, 6 or even 7 years of age, with a maximum age of 13 years at a length of only 75 mm. Unlike some other small-sized species in unproductive environments, individual females continued to spawn successive clutches of eggs though over a much shorter spawning season. The maximum estimated egg production was 824 for a 65-mm fish. Temperature had a strong direct or indirect effect on growth, with significantly lower growth increments in cold summers. At a second Arctic site in eastern Lapland growth rates were higher and maturity earlier, yet clutch size was greatly reduced with a seasonal fecundity estimate of only 314. There were only small differences in size of eggs or larvae between the populations. Evidence from other species indicates that most of the observed changes over the range of the minnow are phenotypic responses to the contrasting environments. However, the different strategies displayed at the two Arctic sites could represent the results of selection for differences in pre- and post-reproductive survival.     

The reproductive biology of an endemic cyprinid,Zacco pachycephalus,in Taiwan

Synopsis Reproductive parameters including body weight-length relationship, condition factor, gonadosomatic index (GSI) and fecundity of an endemic cyprinid,Zacco pachycephalus, were studied from October 1991 to January 1993. Although the condition factor was similar between both sexes, GSI values of female (3.72 to 14.24%) were significantly larger than that of males (0.21 to 2.23%) during the major breeding season. The number of yolky eggs per fish ranged from 459 to 2059. Ovum size distribution, annual GSI value, and recruitment of juvenile fish indicated thatZ. pachycephalus conducted two major spawning activities in spring (February to April) and summer (June to August). The larger GSI value and number of yolky eggs in spring compared to those in summer implies thatZ. pachycephalus has evolved a reproductive style by investing more energy in spring to avoid the damage of summer freshet on its recruitment success. The mating behavior ofZ. pachycephalus is similar to that of otherZacco fishes.     

Reproductive biology of Hemiramphus brasiliensis and H. balao (hemiramphidae): maturation,spawning frequency,and fecundity

Analyses of life-history data show that both the size-specific batch fecundities and the age-specific spawning frequencies differ for two halfbeak species, Hemiramphus brasiliensis, the ballyhoo, and H. balao, the balao. Halfbeak ages were determined from sectioned otoliths; histological data was used to describe oocyte development and estimate spawning frequency; and batch fecundity was measured from counts of whole oocytes in final maturation. Hemiramphus brasiliensis lived longer (4 versus 2 years) and had a higher survival rate (14.9% versus 7.5% annually) than H. balao did. Of the two species the larger and longer-lived congener, H. brasiliensis, reached sexual maturity at a larger size (fork length 198 versus 160 mm). The spawning period of age-0 females was strongly related to season, whereas spawning by older females occurred throughout the year. Reproduction by both species peaked during late spring or early summer, and all mature females were spawning daily during April (H. brasiliensis) or June (H. balao). This is the first demonstration of iteroparity for the family Hemiramphidae. H. brasiliensis had a lower batch fecundity (about 1164 versus 3743 hydrated oocytes for a 100-g female) than H. balao did. Such low batch fecundities are typical of the order Beloniformes, but quite different from those of other fishes that live in association with coral reef habitats. H. balao's higher batch fecundity is consistent with the life-history theory that predicts higher numbers of eggs for shorter-lived species; this is possible because H. balao produces smaller hydrated oocytes than H. brasiliensis (modal diameter about 1.6 versus 2.4 mm). The high spawning frequency of Hemiramphus species compensates for their low batch fecundity. The annual fecundity of both species is similar to that of other reef fish species, after adjusting for body size and spawning frequency. The lifetime fecundity of H. balao was very similar to that of H. brasiliensis, after accounting for the differences in survival for each species. This suggests a fine tuning of different reproductive traits over the entire life cycle that results in roughly equivalent lifetime fecundity for both species.     

保安湖麦穗鱼种群生物学Ⅳ.种群动态

1995年10月至1996年11月运用标志回捕法对保安湖1#试验围拦中麦穗鱼的种群数量作了11次估算,并对种群的动态特征进行了分析。 周年的种群数量变动于0.40-2.45ind·m-2,在5月份最高。不同世代的强度存在较大的差异,1996年世代最强,1996年11月为21,631ind,与同期的1995世代(14,431ind)相比增加了49.9%,死亡率在夏季较高。1995世代周年死亡率为71.7%,1996年11月的数量为4,084ind,与生活史中同期的1994世代(1,515ind)相比,增加了1.7倍。1994世代在1996年繁殖后期的死亡率急剧增加,在产卵季节过后全部死亡。种群活动水平除了与水温有关外,在春季可能主要受繁殖活动的影响。1996年的种群繁殖力为4.05×106粒,其中0+龄的贡献为85.7%.       

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: Female reproductive cycle

In this study, we describe the female reproductive cycle of Philodryas patagoniensis in south Brazil, which was described through morpho‐anatomical and histological analyses. The peak of secondary vitellogenesis occurred during winter–spring (July–December), ovulation in spring (October–December), mating and fertilization in spring–summer (October–February), oviposition in spring–autumn (October–May) and births from late spring to autumn (December–July). The diameter of vitellogenic follicles/eggs was larger in winter–spring than in other seasons. The diameter of the shell glands was also larger in winter–spring. In spite of the clear reproductive peak, gonads only showed reduced activity in the autumn. Therefore, at the individual level, females have a discontinuous cyclical reproduction; in the populational level, the reproductive cycle is seasonal semisynchronous. We support the hypothesis that P. patagoniensis have the ability to produce multiple clutches with long‐term stored sperm. Sexual dimorphism in body size was evident, and females are significantly larger and heavier than males. Larger females were able to produce follicles and eggs in larger amount and size. The maternal body size was positively related to the reproductive effort and fecundity. To conclude, we deliberated about the proximal and distal causes that influence the reproductive traits and patterns of P. patagoniensis.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

Fecundity of the three-spined stickleback, Gasterosteus aculeatus (L.)

The number of eggs spawned by female three-spined sticklebacks Gasterosteus aculeatus (L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.     

Spawning periodicity of three species of Nodilittorina in Hong Kong

The spawning periodicity of Nodilittorina trochoides, N. radiata and N. vidua from two rocky shores of different wave exposure, Big Wave Bay (more exposed site) and Cape d'Aguilar, in Hong Kong was monitored for one year (November 1994–November 1995). The breeding season was similar for the three species, mainly during the summer (June–September). The spawning duration was 9 months for N. vidua and 7 months for the other two littorinids. Spawning was initiated at different times for the two sites. At Big Wave Bay, spawning occurred between May–November for N. trochoides; March–September for N. radiata and March–November for N. vidua. At Cape d'Aguilar, the spawning period of N. trochoides and N. radiata was similar (April–October), whilst for N. vidua, spawning extended up to December. A decrease in monthly fecundity was recorded during July and August at Big Wave Bay and Cape d'Aguilar respectively. A weak relationship was found between the size of reproductive females and egg production. The seasonal fecundity of N. trochoides and N. vidua was similar at both sites and estimated as 10 000 and 7500 eggs per female respectively. Fecundity of N. radiata varied between sites, with 15 000 eggs and 9000 eggs per female being recorded from Cape d'Aguilar and Big Wave Bay respectively.     

Reproductive biology of wahoo, Acanthocybium solandri, off eastern Australia

A dearth of basic biological information for wahoo, Acanthocybium solandri, currently hinders the ability of scientists and managers to assess population sustainability and appropriately manage the dramatically increasing global catch. This study examined the gonads of 382 wahoo collected off eastern Australia during 2008–2011 to quantify their reproductive biology in the region. The overall sex ratio of the sample was 3.2:1 (females:males), however this differed significantly among fishing sectors and areas. The estimated fork length at which 50 % of female wahoo reach maturity was 1,046 mm. Similar to the Atlantic Ocean, female wahoo have a protracted summer spawning season during October-February. The mean spawning frequency of female wahoo was uncertain but may be approximately 2–3 days, with evidence of fish actively spawning on consecutive days. Batch fecundity of females was positively correlated with fish size and estimates ranged between 0.65 and 5.12 million oocytes. Relative fecundity was estimated at 122.0 (±9.7) oocytes per gram of ovary free body weight and did not differ with fish size or throughout the spawning season. Estimation of reproductive parameters such as size- and age-at-maturity may facilitate the construction of per-recruit stock assessments of wahoo in the region.     

Reproduction of the Arctic copepodCalanus hyperboreus in the Greenland Sea-field and laboratory observations

The seasonal vertical migration of adultCalanus hyperboreus Krøyer and their female reproductive biology have been studied in the central Greenland Sea, based on 7-month coverage during one annual cycle. Females dwelled in surface waters only between April and July. Gonad maturation began after the summer descent into deeper waters between September and October in the absence of food. Breeding was assessed from gonad development and egg production experiments. It started around the beginning of November and was mostly completed by March/April, before the spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shallower depths. Males were mostly found during the breeding period, where they inhabited the 500- to 1000-m layer. Female dry weight was highest in August and November and lowest in February. Field observations were supplemented by observations on gonad development and egg production of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fecundity were determined at 0°C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fatter and produced up to 1000 eggs in several clutches deposited at regular intervals.     

Maturation and Reproductive Biology of Female Wild Carp, Cyprinus carpio, in Victoria, Australia

The reproduction of carp Cyprinus carpio L. (Family: Cyprinidae), from Victorian waters in Australia, is studied with detailed analysis of gonad maturation, spawning season, fecundity and oocyte diameter. Results show that carp has a high annual fecundity (AF) (0.12–1.54 million oocytes per fish), which is positively correlated with caudal fork-length (L, mm) and total weight (W, kg) but not age. The relationships between length or weight and AF were statistically significant and best described with the simple linear or quadratic regressions. Mean relative fecundity was 0.163 million eggs kg^–1 whole weight. Egg size was estimated from oocyte diameter in carp from eight stocks. Egg size was proportional to maternal size but not age. Seasonal trends in gonadosomatic indices, together with the changes in the macroscopic and microscopic condition of ovaries, demonstrated that spawning generally peaks during spring–early summer, but also occurs through until autumn and can even start in late winter at some sites. In Victoria, this species is a multiple spawner with asynchronous oocyte development and a protracted spawning season. Stocks generally contain both females that spawn once, and females that spawn repeatedly, within a spawning season. Implications for management for the control of feral carp stocks are discussed.     

Spawning frequency, fecundity, egg weight and spawning type of silver pomfret, Pampus argenteus (Euphrasen) (Stromateidae), in Kuwait waters

Silver pomfret, Pampus argenteus, were collected by fishing with drift gillnets on one spawning ground in Kuwait waters during 1998–2000. Fish size frequency, sex ratio, maturation cycle, spawning frequency, fecundity and egg weight were assessed. The length–weight relationship differed between sexes whereby females were significantly bigger than males. Spawning started in mid‐May and continued until early October. During this time the water temperature ranged from 26.0 to 32.8°C, salinity was ? 39.0‰ and water depth ranged between 5 and 12 m. Large females spawned earlier than young spawners and the overall percentage of males during the spawning period was 70.3%. Spawning occurred after 13.00 h, with peak spawning between 15.00 and 18.00 hours during outgoing tide. Mean daily spawning frequency amounted to 63.2%. Spawning activity was found to be associated with the lunar cycle and spawnings were concentrated during the first and third quarters of the moon period, indicating a semilunar reproduction cycle. It was concluded that a female would spawn at least six times during the season. No change was observed in relative fecundity during the peak spawning season (June–August). Average relative batch fecundity was 176.3 eggs g^?1 somatic weight (SW), corresponding to a relative total fecundity of 1058 eggs g^?1 SW, which is 1.5 times higher than estimates obtained from counting the standing stock of oocytes. Bigger fish produced heavier eggs and the egg weight decreased as the spawning season progressed. Based on gonadal cycles, oocyte size frequency distribution and total fecundity, we concluded that silver pomfret is a multiple batch spawner with indeterminate fecundity.     

Aspects of the spawning biology of the Brazilian sardine, Sardinella brasiliensis (Steindachner, 1879), (Clupeidae)

Biological data, size frequency distribution of intraovarian oocytes, maturity indices and histological observations of the gonads were used to assess the spawning cycle of S. brasiliensis , sampled September 1981–August 1982 throughout the main fishing area off the Brazilian coast (22°S to 28°S). Post-ovulatory follicles are described and classified, and the incidence of mature females displaying these structures was calculated. The main findings were (a) spawning occurred during the spring and summer with a maximum in December and January; (b) spawning occurred throughout the area studied; (c) spawning was fractional; (d) average batch fecundity was 26 000 oocytes per female, or 393 eggs g⁻¹; (e) spawning frequency reached values of approximately 50% during the spawning peak, but was sensibly lower during the other months of spawning activity.     

Seasonal fluctuations in androgen levels in females of the hermaphroditic gag, Mycteroperca microlepis, with an emphasis on juvenile animals

Androgens are known to play many roles in the reproductive physiology of teleosts, but less information exists on the role that they play in the development of larval and juvenile fish. This study examines an observed seasonal cycle of 11-ketotestosterone (11KT) in females of the hermaphroditic gag grouper (Mycteroperca microlepis). Otoliths, gonads, and plasma samples from gag were collected quarterly (spring, summer, fall, and winter), with complete data (age, sex, and androgen levels) obtained from a total of 225 individuals. Ages ranged from zero to 11 years, and all individuals were female. Testosterone (T) peaked in the spring, coincident with spawning, and was low throughout the remainder of the year. The androgen 11KT peaked in summer and declined through the following spring. 11KT levels were negatively correlated with fish size in both the summer and winter, while T was negatively correlated in the summer and positively correlated in the winter. T levels showed little seasonal variation in juveniles (0-1 and 2-3 age groups), but showed a seasonal increase from fall through spring in older fish (4-5 and 6+ age groups). Age 0-1 fish had significantly higher levels of 11KT than the age 4-5 group during the summer and both the 4-5 and 6+ age groups in the winter. The gag is a protogynous hermaphrodite that goes through several ontogenetic shifts during its life, and this seasonal fluctuation in plasma levels of 11KT may play a role in the growth and development, behavior, or control of sex change of gag.     

Batch fecundity of Atlantic mackerel, Scomber scombrus L.

The total annual fecundity of mackerel, Scomber scombrus L., during a spawning season is produced by release of discrete batches of eggs. Total fecundity is then the product of the number of batches times the batch fecundity ( F _bw). An extensive trawl survey of the Western mackerel stock in the NE Atlantic was undertaken in the 1989 spawning season. Batch fecundity was estimated for 298 fish by counting hydrated eggs in ovaries just prior to ovulation. F _bw, expressed as eggs g⁻¹ body weight, varied with latitude: south of 51°N, F _bw= 55.49, s.e. = 2.04, n = 227; between 51°N and 55°N, F _bw= 45.72, s.e. = 3.41, n = 52 and north of 55° N, F _bw= 41.33, s.e. = 5.52, n = 19. It is suggested that as spawning fish migrate northwards the batch size decreases with progress of the spawning season.     

Simultaneous maturation of two discrete oocyte batches in ayu

Ayu Plecoglossus altivelis including amphidromous and landlocked populations, are known for batch spawning. Unusual clutches at ovulation were observed from rearing stocks that were naturally induced to sexual maturation. Two peaks occurred simultaneously in the frequency distribution of egg size, compared to normal fish, which have clutches with unimodal size distribution. The eggs in the small size class could be fertilized, and small-sized larvae hatched from these eggs. To explain the alteration in egg size through divergence from amphidromous to landlocked populations, the role of batch allocation among oocytes is discussed.     

Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter

1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, however, known about the role of fish during winter. 2. We analysed data from 34 lakes studied for 8–9 years divided into three seasons: summer, autumn/spring and winter, and four lake classes: all lakes, shallow lakes without submerged plants, shallow lakes with submerged plants and deep lakes. We recorded how body weight of Daphnia and then cladocerans varied among the three seasons. For all lake types there was a significant positive correlation in the mean body weight of Daphnia and all cladocerans between the different seasons, and only in lakes with macrophytes did the slope differ significantly from one (winter versus summer for Daphnia). 3. These results suggest that the fish predation pressure during autumn/spring and winter is as high as during summer, and maybe even higher during winter in macrophyte‐rich lakes. It could be argued that the winter zooplankton community structure resembles that of the summer community because of low specimen turnover during winter mediated by low fecundity, which, in turn, reflects food shortage, low temperatures and low winter hatching from resting eggs. However, we found frequent major changes in mean body weight of Daphnia and cladocerans in three fish‐biomanipulated lakes during the winter season. 4. The seasonal pattern of zooplankton : phytoplankton biomass ratio showed no correlation between summer and winter for shallow lakes with abundant vegetation or for deep lakes. For the shallow lakes, the ratio was substantially higher during summer than in winter and autumn/spring, suggesting a higher zooplankton grazing potential during summer, while the ratio was often higher in winter in deep lakes. Direct and indirect effects of macrophytes, and internal P loading and mixing, all varying over the season, might weaken the fish signal on this ratio. 5. Overall, our data indicate that release of fish predation may have strong cascading effects on zooplankton grazing on phytoplankton and water clarity in temperate, coastal situated eutrophic lakes, not only during summer but also during winter.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Reproductive Dynamics and Potential Annual Fecundity of South Pacific Albacore Tuna (Thunnus alalunga)

The reproductive biology of albacore tuna, Thunnus alalunga, in the South Pacific Ocean was investigated with samples collected during broad-scale sampling between 2006 and 2011. Histology was done in a single laboratory according to standard protocols and the data analysed using generalized linear mixed-effects models. The sex ratio of albacore was female biased for fish smaller than approximately 60 cm FL and between 85 and 95 cm, and progressively more male biased above 95 cm FL. Spawning activity was synchronised across the region between 10°S and 25°S during the austral spring and summer where sea surface temperatures were ≥24 °C. The average gonad index varied among regions, with fish in easterly longitudes having heavier gonads for their size than fish in westerly longitudes. Albacore, while capable of spawning daily, on average spawn every 1.3 days during the peak spawning months of October to December. Spawning occurs around midnight and the early hours of the morning. Regional variation in spawning frequency and batch fecundity were not significant. The proportion of active females and the spawning fraction increased with length and age, and mature small and young fish were less active at either end of the spawning season than larger, older fish. Batch fecundity estimates ranged from 0.26 to 2.83 million oocytes with a mean relative batch fecundity of 64.4 oocytes per gram of body weight. Predicted batch fecundity and potential annual fecundity increased with both length and age. This extensive set of reproductive parameter estimates provides many of the first quantitative estimates for this population and will substantially improve the quality of biological inputs to the stock assessment for South Pacific albacore.