Reproductive tactics and development of sexually dimorphic structures in a stream-dwelling characid fish (Deuterodon stigmaturus) from Atlantic Forest

The reproductive tactics of Deuterodon stigmaturus were investigated in this study, testing whether the species presents a seasonal or opportunistic life-history strategy in a high latitude Atlantic Forest stream in Brazil. The relation between the development of anal-fin spinelets (sexually dimorphic structures in characids) and the reproductive period of D. stigmaturus was also investigated. The species displayed a seasonal life-history strategy, with the reproductive period occurring between austral spring and summer. The reproductive period was related to increase in temperature and photoperiod, corroborating several studies that suggest positive relation between seasonal reproduction and abiotic predictability. The data indicated total spawning occurring in January, coinciding with the month of greatest rainfall (historical and in the study year). However, the observation of postovulatory follicles in previous months suggests small spawning before January. The development of spinelets on the anal-fin was the only sexual dimorphic trait between males and females. Contrasting with several other studies, seasonal development of anal-fin spinelets was observed in adult males, following the reproductive period and regressing afterwards. Thus, some characid species probably retain this structure throughout the year and others do not, which may be related to life-history strategy differences.     

Annual gonadal cycle and reproduction in Patagonotothen tessellata (Richardson 1845 (Nototheniidae: Pisces) from the Beagle Channel, Argentina

The reproductive biology of Patagonotothen tessellata (Richardson 1845) in the Beagle Channel, Tierra del Fuego, Argentina was analysed from weekly captures over a 3-year period (1987–1989). The spawning periods and lengths thereof were analysed using GSI curves and monthly percentage distributions of maturation stages. Two gonadal maturation cycles and two spawning periods (winter and summer) within 1 year were defined. Also discussed is whether the same specimens are able to mate successfully in winter and summer, and whether the reproductive effort varies between the seasons. Male parental behaviour and the likely consequences on their energy levels are considered.     

Broadcast Spawning by Pocillopora Species on the Great Barrier Reef

The coral genus Pocillopora is one of the few to include some species that broadcast spawn gametes and some species that brood larvae, although reports of reproductive mode and timing vary within and among species across their range. Notably, the ubiquitous Pocillopora damicornis has been described as both a brooder and spawner, although evidence of broadcast spawning is rare. Here, we report observations of broadcast-spawning in four species of Pocillopora on the Great Barrier Reef (GBR), including P. damicornis. All species spawned predictably during the early morning, two days following the full moon, and spawning was observed in multiple months over the summer period (November to February). Eggs and sperm were free-spawned concurrently. Eggs were negatively buoyant and contained Symbiodinium. This newfound knowledge on the mode, timing and regularity of broadcast spawning in Pocillopora spp. on the GBR brings us one step closer to elucidating the complex reproductive ecology of these species.     

Phytoplankton as a stimulus for spawning in three marine invertebrates

A distinct annual reproductive cycle with spring spawning was observed in Strongylocentrotus droebachiensis Müller, Tonicella lineata Wood and Tonicella insignis Reeve. This study gives evidence that the cue for spawning in these species is the spring phytoplankton bloom. In 1973 spawning occurred abruptly in early April at the time of the spring phytoplankton outburst, but in 1974 spawning was less abrupt corresponding to the slow development of the phytoplankton bloom in that year. Animals were collected prior to spawning and maintained in the laboratory under various temperature and light regimes: at 5 ° and 14 °C in darkness, and at 5 ° and 14 °C in light conditions similar to those in the field. These animals did not spawn when spawning occurred in the field, but animals returned to the field from the laboratory did spawn. In the laboratory a large proportion of animals spawned when they were exposed to phytoplankton collected with a 50μm mesh net. The results suggest that some substance bound to or released by phytoplankton stimulates spawning. For species with planktotrophic larvae the synchronization of spawning with the phytoplankton bloom increases the probability of favourable food and temperature conditions for the development of the larvae and juveniles.     

Not All Offspring Are Created Equal: Variation in Larval Characteristics in a Serially Spawning Damselfish

The way organisms allocate their resources to growth and reproduction are key attributes differentiating life histories. Many organisms spawn multiple times in a breeding season, but few studies have investigated the impact of serial spawning on reproductive allocation. This study investigated whether resource allocation was influenced by parental characteristics and prior spawning history in a serial spawning tropical damselfish (Pomacentrus amboinensis). The offspring attributes of isolated parents of known characteristics were monitored over a 6-week breeding period in the field. Smaller females produced larvae of longer length and larger energy reserves at hatching. This finding is contrary to several other studies that found larger females produce offspring of greater quality. We found that resource allocation in the form of reproductive output was not influenced by the number of spawning events within the breeding season, with larger females producing the greatest number of offspring. Larval characteristics changed as spawning progressed. There was a general decline in length of larvae produced, with an increase in the size of the larval yolk-sac, for all females regardless of size as spawning progressed. This trend was accentuated by the smallest females. This change in larval characteristics may reflect a parental ability to forecast unfavourable conditions as the season progresses or a mechanism to ensure that some will survive no matter what conditions they encounter. This study highlights the importance of accounting for temporal changes in reproductive allocation in studies of reproductive trade-offs and investigations into the importance of parental effects.     

Influence of temperature during four following spawning seasons on the spawning effectiveness of common bream,Abramis brama (L.) under natural and controlled conditions

The common bream, Abramis brama (L.) in Kortowskie Lake (north-eastern Poland) usually spawn when the water temperature during the late spring rises to 20 °C. The optimal water temperature for embryonic development of this population is 21 °C. However, in some cases, the temperatures of the spawning grounds during bream spawning are much higher, becoming semi-lethal or even lethal for bream embryos. The aim of the study was to investigate the natural and artificial spawning effectiveness of bream during a 4-year study regarding the reproductive effectiveness of the wild bream population in relation to thermal fluctuation (optimal and semi-lethal) of their ecosystem during the natural spawning season. During four following seasons, the bream spawners, as well as the eggs, were collected from the spawning grounds and incubated at optimal (21 °C) and semi-lethal (23 °C) temperatures. The spawning of mature bream was artificially induced and the obtained eggs were also incubated at the same temperatures. The period of observed spawners on the spawning grounds was different in different years: the longest time of bream spawning was in the second year of the study and the shortest was during the third year of the study. In the last year, a decrease in water temperature caused a break in the spawning. Thermal changes in water temperature during the spawning season may have caused a high mortality level of bream embryos and decreased the recruitment of the next species generation.     

Participatory fishery monitoring is successful for understanding the reproductive biology needed for local fisheries management

Tropical fisheries management should rely on reproductive biology to inform management regulations; however, this information is often lacking and can be highly variable over in space and time. It is unfeasible for many fisheries, especially data-poor ones that are typical of tropical reefs to collect the necessary information on reproductive biology. One solution is a participatory approach where local fishers, scientists, and regulating agencies gather the necessary information to assess population variability for important management metrics such as size at maturity, reproductive output, and spawning seasons. Through collaborations with local fishers, we developed a monitoring program to gather population-level information on the reproductive characteristics of the convict tang, Acanthurus triostegus sandvicensis. We examined four locations across the main Hawaiian Islands and found size at maturity [size at which 50% of individuals are mature (L₅₀)] to vary among locations, with interpopulation differences in maturity?~?20% of the fish’s total length. Larger individuals produced more eggs and spawned more often than smaller individuals. A semilunar spawning pattern was observed, with group spawning occurring near the new and full moons. However this pattern was variable by year and location, likely resulting from different seasonal peaks in spawning by location. Gonadosomatic index (t?=?2.41, p-value?=?0.02) and spawning fraction (z?=?2.92, p-value?<?0.01) were both significantly higher in 2014 compared to 2013, suggesting annual variability in reproductive output. Participatory fishery monitoring proved successful in collecting biological needed for management and improved understanding of population reproductive variability.     

Fitness and behavioral correlates of pre-stress and stress-induced plasma cortisol titers in pink salmon (Oncorhynchus gorbuscha) upon arrival at spawning grounds

Semelparous Pacific salmon (Onchorynchus spp.) serve as an excellent model for examining the relationships between life history, behavior and individual variation in glucocorticoid (GC) stress hormone levels because reproductive behaviors are highly variable between individuals and failure to reproduce results in zero fitness. Pink salmon (O. gorbuscha) were intercepted upon arrival at the spawning grounds across three time periods. Pre-stress and stress-induced plasma cortisol concentrations were assessed in relation to behavior, longevity and reproductive success. Results revealed differences between sexes and with arrival time. The study period marked a year of high reproductive success and only nine females (12% of sample) failed to spawn. Female pre-spawn mortalities were characterized by significantly elevated stress-induced cortisol concentrations and decreased longevity as well as pre-stress cortisol above the normal range in pink salmon from the study area. Interestingly, reproductive behaviors were only associated with pre-stress cortisol levels. For females, aggression and mate interaction time were reduced in individuals with elevated pre-stress cortisol concentrations. In males, a similar negative relationship between pre-stress cortisol concentration and mate interaction time was detected. The observed behavioral correlations are likely a factor of social status where dominant individuals, known to have higher reproductive success, are characterized by lower cortisol levels relative to subordinate conspecifics. Findings show both elevated pre-stress and stress-induced cortisol concentrations at arrival to the spawning grounds to be associated with reduced survival.     

Annual variations in the reproductive traits of Pomatoschistus microps in a Mediterranean lagoon undergoing environmental changes: evidence of phenotypic plasticity

The spawning period of the common goby Pomatoschistus microps from 1993 to 1997 in the Vaccarès lagoon did not vary, except in 1997 when it was longer due to the reproduction of the young-of-the-year. Egg size and number, and reproductive allocation varied greatly with one year to another. Female common gobies increased both their fecundity per spawning act and their egg size from 1993 to 1995. The annual variation in the reproductive effort suggests a high phenotypic plasticity of reproductive traits in P. microps , in the face of environmental perturbations. In winter 1993–1994, a centennial flood of the Rhône River caused major hydrological changes in the lagoon in less than 1 week, affecting many invertebrates and fish for several years. The reproductive investment of the common goby increased, possibly as a consequence of those environmental changes.     

Reproductive condition and occurrence of intersex in bighead carp and silver carp in the Missouri River

Little is known about the reproductive biology of the exotic bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix in the Missouri River. In order to fill this gap in understanding, herein is described the reproductive condition of these Asian carps. Evidence is presented which indicates that bighead and silver carp in the Missouri River have a protracted spawning period that extends from early spring through fall and some individual bighead and silver carp are spawning multiple times during a reproductive season. Although bighead and silver carps are successfully maturing and spawning in the Missouri River some reproductive abnormalities such as intersex, atresia, and sterility were observed. Knowledge of the reproductive activity of these invasive carps may be useful to resource managers tasked with their control. Furthermore, the reproductive abnormalities observed should be considered when evaluating the environmental condition of the Missouri River relative to supporting a healthy fish fauna.     

Interannual variability in reproductive traits of the Patagonian toothfish Dissostichus eleginoides around the sub‐Antarctic island of South Georgia

Commercial fisheries data, collected as part of an observer programme and covering the period 1997–2014, were utilized in order to define key reproductive traits and spawning dynamics of the Patagonian toothfish Dissostichus eleginoides at South Georgia. Multi‐year spawning site fidelity of D. eleginoides was revealed through the identification of previously unknown spawning hotspots. Timing of female spawning was shown to have shifted later, leading to a shorter spawning duration. A decrease in length and mass of female and male spawning fish and a reduced number of large spawning fish was found, evidence of a change in size structure of spawning D. eleginoides. During the study period fewer later maturity stage females (including spawning stage) were observed in conjunction with increased proportions of early stage female D. eleginoides. The findings are discussed in the context of reproductive success, with consideration of the possible effects such spawning characteristics and behaviours may have on egg and larval survival. This work presents the first long‐term assessment of D. eleginoides spawning dynamics at South Georgia and provides valuable knowledge for both the ecology of the species and for future fisheries management of this commercially important species.     

Biannual Spawning and Temporal Reproductive Isolation in Acropora Corals

Coral spawning on the oceanic reef systems of north-western Australia was recently discovered during autumn and spring, but the degree to which species and particularly colonies participated in one or both of these spawnings was unknown. At the largest of the oceanic reef systems, the participation by colonies in the two discrete spawning events was investigated over three years in 13 species of Acropora corals (n = 1,855 colonies). Seven species spawned during both seasons; five only in autumn and one only in spring. The majority of tagged colonies (n = 218) spawned once a year in the same season, but five colonies from three species spawned during spring and autumn during a single year. Reproductive seasonality was not influenced by spatial variation in habitat conditions, or by Symbiodinium partners in the biannual spawner Acropora tenuis. Colonies of A. tenuis spawning during different seasons separated into two distinct yet cryptic groups, in a bayesian clustering analysis based on multiple microsatellite markers. These groups were associated with a major genetic divergence (G”_ST = 0.469), despite evidence of mixed ancestry in a small proportion of individuals. Our results confirm that temporal reproductive isolation is a common feature of Acropora populations at Scott Reef and indicate that spawning season is a genetically determined trait in at least A. tenuis. This reproductive isolation may be punctuated occasionally by interbreeding between genetic groups following favourable environmental conditions, when autumn spawners undergo a second annual gametogenic cycle and spawn during spring.     

Interannual fluctuations in recruitment and growth of the sardine,Sardinops melanostictus,in the sea of Japan and adjacent waters

Recruitment and growth of the sardineSardinops melanostictus fluctuated markedly in the Sea of Japan and adjacent waters between 1978 and 1993. Stock size was calculated using Virtual Population Analysis and average body length in each age class was determined by the number of annual rings on the scales. There is an inverse correlation between average water temperature at a depth of 50 m in the coastal area of the mainland of Japan in winter (January to March) and recruitmentR defined as the number of individuals at 1 year old. There is also an inverse correlation between spawning stock sizeE and reproductive success in (R/E). A multiple regression model using spawning stock size and water temperature in winter as independent variables can explain 73% of variance in reproductive success. It suggests that both density-dependent and density-independent factors perform important roles determining reproductive success. There is an inverse correlation between body length and stock size and this suggests that there is a density-dependent effect on the growth of the sardine.     

Population genetics of a Chinese endemic, <Emphasis Type="Italic">Gymnocypris potanini</Emphasis> Herzenstein,threatened by population isolation: conflicting patterns between microsatellites and mitochondrial DNA

The arrival of the rains and the hydrological changes they cause are essential in the reproductive cycle of Neotropical migratory fishes, but their association with the onset of migration is still poorly understood. This study aimed to determine the role played by rainfall, hydrological changes, and the lunar cycle as triggers for migration of Prochilodus costatus (Prochilodontidae) in the upper São Francisco River, Brazil. In total, 132 individuals were fitted with radiotelemetry transmitters over three consecutive spawning seasons. Spawning migration began with the onset of the rains from late September to mid-December. Individuals exhibited a strong preference for initiating migration at the beginning of the rainy season, when river discharge is low, in days with positive changes in water level, and at times of new or waxing moon. The fraction of the population that initiates migration each year appears to be dependent on rainfall, indicating that P. costatus may be a partial migrant. The results show that P. costatus and, possibly, other migratory Neotropical fish, rely on different but interconnected environmental cues to trigger their spawning migration, ensuring that individuals migrate in time to reach their spawning grounds and find appropriate environmental conditions for spawning.     

Female nuptial signal advertises spawning readiness in a population of <Emphasis Type="Italic">Halichoeres margaritaceus</Emphasis> on the Great Barrier Reef,Australia

Females of some polygynous fish species display female nuptial signals (FNSs), advertising spawning readiness to potential mates. Halichoeres margaritaceus, a polygynous coral reef fish, reportedly display red belly color and a unique bobbing behavior as FNSs advertising spawning readiness. In this study, I examined whether FNSs were observed in an H. margaritaceus population in Australia. Females in this study displayed red belly color as an FNS, although at a lower intensity than that reported in a Japanese population. Contrary to observations made in the Japanese population, bobbing behavior performed by females in this study showed no temporal trend as spawning approached, indicating bobbing behavior did not function as an FNS in the Australian population. The role of local selective pressures on FNS intensity and lifetime reproductive benefits H. margaritaceus may potentially gain in utilizing FNSs are briefly discussed.     

Batch fecundity and spawning frequency of invasive Hemiculter leucisculus (Basilewsky, 1855) in Erhai Lake,China

Hemiculter leucisculus are multiple spawners with indeterminate fecundity, although previous fecundity estimates have assumed a determinate spawning pattern. Batch fecundity and spawning frequency of H. leucisculus were studied in Erhai Lake, China, in which the fish, as an exotic species, has become a successful colonizer. Spawning frequency was 16.05 %, as determined from the percent of females with postovulatory follicles 12 to 36 h old during the peak reproductive period (from May 27 to August 8). The average interval between spawning was 6.2 days and there were more than 16 total spawning batches during the peak reproductive period. The average batch fecundity (mean ± SD) was 11,934?±?5,921 hydrated oocytes in 40 females (standard length or SL: 9.1–14.4 cm), while relative batch fecundity was 560?±?137 eggs g^?1 wet weight. The total potential annual fecundity was approximately 190,944 oocytes over the whole spawning season and was much higher than the estimated standing stock (31,585 oocytes) of yolked oocytes (36 females, SL: 9.5–16.2 cm) at the beginning of the spawning season in April 2010. This high annual fecundity is likely to have contributed to successful invasion of Erhai Lake by H. leucisculus.     

Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern Bluefin Tuna,Thunnus maccoyii

Knowledge of spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the spawning ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the spawning ground slightly later and depart earlier in the spawning season relative to large fish. All females were mature and the majority were classed as spawning capable (actively spawning or non-spawning) with a very small proportion classed as regressing. The fraction of females spawning per day decreased with fish size, but once females start a spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of spawning and non-spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the spawning ground as a function of fish size (if known) and demographic data for the spawning population to provide a time series of relative annual fecundity for SBT.     

Spawning frequency in the eastern Australian river garfish, Hyporhamphus regularis ardelio (Hemiramphidae)

Patterns in the timing of spawning of the eastern Australian river garfish Hyporhamphus regularis ardelio were investigated by sampling fish throughout 24?h during their peak spawning period. Patterns in gonadosomatic indices, the presence of hydrated oocytes and post-ovulatory follicles in histological ovary sections, together with previously demonstrated polymodal distributions of oocytes undergoing final maturation, indicated that river garfish were capable of spawning at any time during the 24?h period. Spawning had either recently occurred or was imminent in all females sampled suggesting that river garfish could spawn multiple times in a given season. Although energy resources are used in the production of low numbers (<2500) of large (~2.5?mm diameter) eggs per batch, total fecundity during the reproductive season may be elevated through multiple spawning events. Implications of these findings on current fishery management regulations are discussed.     

Facultative semelparity in capelin Mallotus villosus (Osmeridae)-an experimental test of a life history phenomenon in a sub-arctic fish

Two alternative reproductive modes are present in fishes and reflect the age-specific mortality encountered through ontogenesis. Life-history hypotheses suggest that semelparity (i.e. death after a single reproductive event) evolves when the ratio of juvenile to adult survival is relatively high. Conversely, a relatively low ratio of juvenile to adult survival will favour iteroparity (i.e. death after two or more reproductive events). Fisheries management associates capelin (Mallotus villosus) spawning with mass mortality and semelparity even though life history models developed for this species suggest that females may follow an iteroparous trajectory. Capelin may spawn either inter-tidally on the beach or offshore in deeper, ocean waters but post-spawning survival and potential iteroparity has been notoriously difficult to assess in natural populations. Through a series of aquarium experiments we tested post-spawning survivability in a beach spawning and an ocean spawning population. The findings demonstrate that capelin which spawn offshore are absolute semelparous (death of both genders) while beach spawning capelin are iteroparous irrespective of sex. Beach spawning capelin regenerated ripe gonads from one spawning season to the next and provides the first conclusive evidence that capelin is physiologically capable of an iteroparous reproductive mode. The potential physical and biological processes which generate certain reproductive patterns in capelin are summarized and discussed in relation to life history hypotheses. We suggest that capelin is a facultative semelparous species in which dynamic changes within the semelparity-iteroparity continuum may occur as a result of subtle interactions between the spawning habitat, physical forcing, and predatory pressure.