Timing Of Spawning Research Articles

Predicting potential spawning areas of European bass, Dicentrarchus labrax, in the Irish and Celtic seas

Marine fish species that form spawning aggregations are often vulnerable to exploitation, such as the European bass (Dicentrarchus labrax). Information on bass spawning aggregations is not well resolved temporally and spatially. Otolith daily growth increment (DGI) counts were conducted on 0-group bass collected in July-August 2014 & 2019 from seven settlement estuaries in the Irish and Celtic seas, to estimate the timing of spawning. These timings parameterised three-dimensional hydrodynamic and Lagrangian particle tracking models, run in reverse, to identify probable spawning locations. Estimated spawning occurred between April-May (inshore and offshore) < 200 km from each settlement area. At least two broad spawning areas were predicted: the central Irish Sea that led to post-larval recruitment in north Wales and northwest England, and the southern Irish Sea/Celtic Sea that led to post-larval recruitment in south Wales. Results indicate the current seasonal closure for northern stock bass may not protect spawning events that drive recruitment into settlement sites in Wales and northwest England. Surface temperatures and wind- and tide-driven surface currents determined the connectivity between spawning and settlement sites. Atmospheric drivers are expected to change in the future and management needs to account for potential regional shifts in spawning times and locations.

Negative phototaxis in the photosymbiotic sea anemone Aiptasia as a potential strategy to protect symbionts from photodamage

Photosymbiotic cnidarians generally seek bright environments so that their symbionts can be photosynthetically active. However, excess light may result in a breakdown of symbiosis due to the accumulation of photodamage in symbionts causing symbiont loss (bleaching). It is currently unknown if photosymbiotic cnidarians sense light only to regulate spawning time and to facilitate predation, or whether they also use their light-sensing capacities to protect their symbionts from photodamage. In this study, we examined how the sea anemone Aiptasia changes its behaviour when exposed to excess light. We reveal that Aiptasia polyps, when carrying symbionts, contract their bodies when exposed to high light intensities and subsequently migrate away in a direction perpendicular to the light source. Interestingly, this negative phototaxis was only evident under blue light and absent upon UV, green and red light exposure. Non-symbiotic Aiptasia did not exhibit this light response. Our study demonstrates that photosymbiotic Aiptasia polyps display negative phototactic behaviour in response to blue light, and that they also can perceive its direction, despite lacking specialized eye structures. We postulate that Aiptasia uses blue light, which penetrates seawater efficiently, as a general proxy for sunlight exposure to protect its symbionts from photodamage.

Репродуктивна динаміка ропухи сірої Bufo bufo (Linnaeus, 1758) і жаби трав’яної Rana temporaria (Linnaeus, 1758) як один з ключових етапів їх сезонного циклу

The results of research on the reproductive dynamics of the key amphibian species of the Ukrainian Roztochchia are presented. Since reproduction is one of the most important and key stages of the seasonal cycle of amphibians, special attention was paid to this period. We used classic and typical methods of recording reproductive activity of amphibians: route records, searching for dead amphibians on the roads, vocalization methods and installation of temporary protective barriers that prevent amphibians from crossing the road. Therefore, amphibians of the genera Rana and Bufo belong to the species with a sudden type of reproduction. We included representatives of the genera Lissotriton, Triturus, Bombina, Hyla, and Pelophylax to the long-term breeding species. In particular, temporary protective barriers gave us indicative and clear concepts regarding the temporal peaks and troughs of reproductive migrations of the studied amphibian species, as well as the direction of movement to reproductive and trophic habitats. Comparing the beginning of reproductive activity and its course throughout the season, we can see certain differences between the model species B. bufo and R. temporaria, in particular, the choice of breeding ponds, the time of spawning and the period of activity of sexually active individuals. Reproductive activity of the common frog occurs in the first half of March — mid-April. In the second half of April, we caught common frogs on both sides of the barriers, which indicates a “turning point” in the sexual activity of this species. Although the common toad is the first to appear after hibernation, spawning occurs approximately a decade later than that of the common frog but takes a little longer. We believe that such research should be continued regularly and our results will encourage herpetologists to further and long-term research.

Reproductive biology and length-weight relationship of the Pool Barb Puntius sophore (Hamilton, 1832) in Mymensingh, Bangladesh

The study was conducted within the Freshwater station of the Bangladesh Fisheries Research Institute in Mymensingh from November 2019 to October 2020. The main objectives were to acquire additional knowledge regarding length-weight connection, condition factor, sex ratio, gonadosomatic index, and fecundity of P. sophore. It was possible to determine the spawning season each month by comparing the levels of the gonadosomatic index for the two sexes. Both sexes of the P. sophore species showed negative allometric growth, as indicated by the length-weight relationships of TW=0.0165TL2.852 for females and TW=0.035TL2.956 for males. For females, the average condition factor was 1.17±0.096, while for males, it was 3.24±0.19. Both times, the condition factor's value was high (&gt;1), demonstrating that both sexes are in good health. From collected fish, 147 (55.12%) of the 264 fish samples that were taken were females, whereas 117 (44.88%) were males (Females: Males=1:0.82). The chi-square test showed that the male-to-female ratio during the sample months was not significantly different from 1:1 (χ2= 0.15, p&gt;0.05). The spawning season extended from May through July, with June representing both sexes' peak spawning time. According to the study, the month of June had the highest absolute fecundity, which was 7829 and the absolute fecundity value was found to be lowest in the month of October 803 with an average value of about 3560 throughout the study period. For the management and protection of this species, this data will be valuable to researchers and those who decide on fisheries policy.

Trends in larval densities, spawning timing, and site quality of capelin (Mallotus villosus) across bays and habitats in Newfoundland, Canada

Abstract Capelin is a short-lived forage fish species that underwent a population collapse in 1991 on the Newfoundland and Labrador Shelf, Canada (Northwest Atlantic Fisheries Organization Divisions 2J3KL) and has not recovered. The collapsed stock is characterized by delayed spawning timing and low recruitment. As year-class strength is set early in life, long-term larval monitoring at an intertidal spawning site in Trinity Bay (TB) is used as a proxy for stock-wide recruitment. Capelin spawn at both intertidal and subtidal habitats; however, there is minimal larval information from bays with a high incidence of subtidal spawning. We aimed to (i) compare inter-annual trends in temperatures, timing of spawning, and annual larval densities between two northeastern bays [TB and Notre Dame Bay (NDB)] and (ii) compare habitat quality metrics and larval densities between subtidal and intertidal sites in NDB. The date of first spawning in TB and NDB was positively correlated, suggesting that years with delayed spawning are experienced shelf-wide. While larval density was lower in NDB compared to TB, inter-annual trends were similar. In NDB, larval densities at both intertidal and subtidal spawning habitats were similar within a year, but temperatures and the proportion of dead eggs were lower at subtidal sites. These habitat quality metrics, however, were not related to annual larval density. These findings improve our knowledge on sources of capelin productivity, including the potential importance of subtidal spawning to recruitment dynamics.

Estimating peak breeding season, size at first maturity and variation in fecundity and egg-size at different sizes of Hilsa (Tenualosa ilisha)

Hilsa shad, Tenualosa ilisha, has recently gained momentum due to its taste, nutrition and demand. Imposing ban at peak breeding and setting up a minimum capture size are two of the most effective tools for conservation and management of any fish species. Although, Bangladesh government has been imposing ban on a particular time and set the minimum legal size, there is still contradictory information on these two issues. That is why, a study was carried out to determine peak season of breeding and first maturity of Hilsa collected across the natural habitats in Bangladesh. Variation in fecundity and egg-size at different sizes were also investigated. Peak breeding season was identified observing gonadosomatic index of female Hilsa all the year round. First maturity was estimated with Probit analysis.Based on the gonadosomatic index of gravid females, peak breeding season was identified as late October to early November in this study. However, another minor peak was found in February–March. The highest GSI value (12.1) was observed in October–November, which indicates the peak time of spawning. The size at maturity (M50) of female Hilsa was estimated as 31 cm total length. A significant variation was observed in egg sizes between the left and right lobes of the fish (t (24) = 2.42, p = 0.02), and between the parts of the same lobe (p = 0.03). However, fish length and weight had no effect on egg size(for egg-size vs. fish length, r = -0.009, p = 0.966; and for egg size vs. body weight, r = 0.132 and p = 0.530). The average egg count from left lobe and right lobe were recorded as 0.375 ± 0.16 million, 0.371 ± 0.17 million. Total fecundity was counted as 0.745 ± 0.33 million. A significant positive correlation was noticed between length, weight, and total fecundity (r = 0.7 for total fecundity vs. body weight; r = 0.6 for of total fecundity vs. length). No significant variation was observed in fecundity between the left and right lobe (p = 0.6) and among three parts of a lobe (p = 0.3). The size of eggs varied between two lobes and among different parts of a lobe. The eggs from middle part were bigger in size than the other parts. The findings of our study will help conserve and manage the natural population of Hilsa (T. ilisha) in Bangladesh and contribute to the wider scientific community.

Migration timing and tributary use of spawning flannelmouth sucker (Catostomus latipinnis).

Spawning phenology and associated migrations of fishes are often regulated by factors such as temperature and stream discharge, but flow regulation of mainstem rivers coupled with climate change might disrupt these cues and affect fitness. Flannelmouth sucker (Catostomus latipinnis) persisting in heavily modified river networks are known to spawn in tributaries that might provide better spawning habitat than neighboring mainstem rivers subject to habitat degradation (e.g., embedded sediments, altered thermal regimes, and disconnected floodplains). PIT tag data and radio telemetry were used to quantify the timing and duration of flannelmouth sucker tributary spawning migrations in relation to environmental cues in McElmo Creek, a tributary of the San Juan River in the American Southwest. We also tested the extent of the tributary migration and assessed mainstem movements prior to and after tributary migrations. Additionally, multiyear data sets of PIT detections from other tributaries in the Colorado River basin were used to quantify interannual and cross-site variation in the timing of flannelmouth sucker spawning migrations in relation to environmental cues. The arrival and residence times of fish spawning in McElmo Creek varied among years, with earlier migration and a 3-week increase in residence time in relatively wet years compared to drier years. Classification tree analysis suggested a combination of discharge- and temperature-determined arrival timing. Of fish PIT tagged in the fall, 56% tagged within 10 km of McElmo Creek spawned in the tributary the following spring, as did 60% of radio-tagged fish, with a decline in its use corresponding to increased distance of tagging location. A broader analysis of four tributaries in the Colorado River basin, including McElmo Creek, found photoperiod and temperature of tributary and mainstem rivers were the most important variables in determining migration timing, but tributary and mainstem discharge also aided in classification success. The largest tributary, the Little Colorado River, had more residential fish or fish that stayed for longer periods (median = 30 days), whereas McElmo Creek fish stayed an average of just 10 days in 2022. Our results generally suggest that higher discharge, across years or across sites, results in extended use of tributaries by flannelmouth suckers. Conservation actions that limit water extraction and maintain natural flow regimes in tributaries, while maintaining open connection with mainstem rivers, may benefit migratory species, including flannelmouth suckers.

How Are Man-Made Changes in Freshwater Flow Related to the Abundance of Juvenile Estuarine Fishes?

Changes in freshwater flow to estuaries can cause a suite of ecosystem impacts including eutrophication and alterations to plant communities, zooplankton populations, and other biota. In southwest Florida, historical manipulation of freshwater flow due to development, canals, and drainage ditches is pervasive. Because there are estuaries with reduced, increased, and relatively natural freshwater flow, this region presents an ideal system to study how these changes relate to downstream fish abundances. We used a 20-year trawl dataset focused on juvenile and small-bodied fish from three mangrove-lined sub-estuaries with contrasting flow conditions in southwest Florida’s Ten Thousand Islands to identify important environmental and temporal variables influencing fish populations. We used generalized additive models to investigate total fish abundance, species richness, diversity, and the abundances of 23 ecologically, recreationally, or commercially important species and describe their relationships with important environmental and temporal variables. While salinity and temperature had species-specific relationships with fish abundances, seasonality, interannual variability, and sub-estuary were more closely related to fish than salinity and temperature in most cases. Only 8 of 23 species responded most strongly to temperature, and only 1 species responded most strongly to salinity. This suggests that for most species in our study, temporal factors such as timing of spawning and recruitment variability had stronger relationships with the structure of fish populations than changes in freshwater flow. This work quantified how changes in freshwater flow, using salinity as a proxy, may relate to downstream fish abundances and therefore the potential implications of planned watershed restoration that is part of the Comprehensive Everglades Restoration Plan.

An Evolutionary Strategy for Spawning Habitat Selection by Pseudopungtungia tenuicorpa.

In this study, we hypothesized that the limited geographical distribution of Pseudopungtungia tenuicorpa in South Korea is closely related to the local abundance of their preferred spawning habitats. Eggs of P. tenuicorpa were most frequently observed in cracks smaller than 5 cm, followed by the nests of other fish, such as Coreoperca herzi. Although eggs of P. tenuicorpa were also found in cracks larger than 6 cm, most of them were consumed or damaged by other fish. However, the number of P. tenuicorpa eggs spawned in cracks smaller than 5 cm remained similar to the number of eggs at the time of initial spawning, even after 9 days. The strong preference of P. tenuicorpa for cracks smaller than 5 cm was found to influence the geographical distribution of P. tenuicorpa in South Korea. In the upper reaches of the Han River, the ratio of cracks smaller than 5 cm is higher than that in the Geum River and in the Nakdong River, which contributes to the stable population growth of P. tenuicorpa there. In the future, management strategies to maintain/restore cracks smaller than 5 cm should be reviewed for the preservation of this endemic fish in South Korea.

Ageing of juvenile coral grouper (Plectropomus maculatus) reveals year-round spawning and recruitment: implications for seasonal closures.

Temporal patterns in spawning and juvenile recruitment can have major effects on population size and the demographic structure of coral reef fishes. For harvested species, these patterns are crucial in determining stock size and optimizing management strategies such as seasonal closures. For the commercially important coral grouper (Plectropomus spp.) on the Great Barrier Reef, histological studies indicate peak spawning around the summer new moons. Here we examine the timing of spawning activity for P. maculatus in the southern Great Barrier Reef by deriving age in days for 761 juvenile fish collected between 2007 and 2022, and back-calculating settlement and spawning dates. Age-length relationships were used to estimate spawning and settlement times for a further 1002 juveniles collected over this period. Unexpectedly, our findings indicate year-round spawning activity generates distinct recruitment cohorts that span several weeks to months. Peak spawning varied between years with no clear association with environmental cues, and little to no alignment with existing seasonal fisheries closures around the new moon. Given the variability and uncertainty in peak spawning times, this fishery may benefit from additional and longer seasonal closures, or alternative fisheries management strategies, to maximize the recruitment contribution from periods of greatest reproductive success.

Social Environment Influences the Temporal Dynamics of Sneak-Spawning in a Fish with Alternative Reproductive Tactics.

AbstractSeveral predictions of sperm competition theory are not well supported empirically. One potential reason is that most current theory and empirical research ignore how the social environment influence the temporal dynamics of mating. We propose that understanding these dynamics is key to understanding sexual selection and improving the predictive power of theory. To demonstrate the importance of these dynamics, we quantify how males' social role, interactions among males, and current social environment influence the timing of mating in Symphodus ocellatus, a species with three alternative male reproductive tactics. Nesting males spawn synchronously with females; sneakers and satellites sneak-spawn with some time delay. Satellites also cooperate with nesting males. We found that satellites have shorter sneak-spawning delays than sneakers, a benefit of their cooperation with nesting males. Sneak-spawning delays decreased with increasing nest activity for sneakers but not for satellites, suggesting that sneakers may benefit from increased sperm competition intensity. Current sperm competition models ignore this potential benefit, which may be why the prediction that males should decrease investment when sperm competition involves more than two males is not well supported. Our study provides insight into mechanisms that drive variation in the timing of spawning, which could explain mismatches between theoretical and empirical results.

Year-round spawning of three tropical Cypriniformes fishes in Southeast Asia

Present knowledge on spawning seasonality of freshwater fishes in tropical Asia and their relationship with environmental factors remains limited. Three Southeast Asian Cypriniformes fishes, Lobocheilos ovalis, Rasbora argyrotaenia and Tor Tambra, found in rainforest streams in Brunei Darussalam were studied on a monthly basis for a period of 2 years. To assess spawning characteristics, seasonality, gonadosomatic index and reproductive phases were examined from 621 L. ovalis, 507 R. argyrotaenia and 138 T. tambra. This study also examined environmental factors such as rainfall, air temperature, photoperiod and lunar illumination that may influence the timing of spawning of these species. We found that L. ovalis, R. argyrotaenia and T. tambra were reproductively active throughout the year but did not find that spawning in these species were associated with any of the investigated environmental factors. Our study showed that the non-seasonal reproductive ecology found in the tropical cypriniform species is distinctly different from that of temperate cypriniforms, which are known to follow spawning seasonality, suggesting an evolutionary adaptation to ensure their survival in an unstable environment. The reproductive strategy and ecological responses found in the tropical cypriniforms might be shifted in response to climate change scenarios in the future.

Automated acoustic detection of river herring (Alewife and Blueback Herring) spawning activity

AbstractObjectiveWe used passive acoustic monitoring (PAM) and automatic detection of spawning splashes to examine the timing and environmental drivers of spawning in river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis).MethodsAcoustic recordings of spawning splashes were collected from March to May 2021 in the Choptank River, Maryland, using an AudioMoth recorder. Recordings were analyzed using a random forest model on the Rainforest Connection ARBIMON platform to determine hourly presence–absence of splashes.ResultAt a seasonal scale, our results suggested two peaks in spawning activity: early March and mid‐April, corresponding with the known phenologies of Alewife and Blueback Herring. Hourly patterns in spawning activity suggested distinct diel cycles, with spawning most concentrated at dawn. In contrast, sonar fish counts collected for 1 week during the season indicated that migration occurred throughout daylight hours. We also found a potential relationship between spawning activity and the presence of great blue herons Ardea herodias.ConclusionOverall, our results demonstrate that PAM can be an efficient and affordable method for studying the spawning ecology of anadromous fish.

Reproductive ecology of the soft-shell clam (Mya arenaria) in Eastern New Brunswick, Canada: Assessing size-at-maturity and spawning time to inform fisheries management

Soft-shell clams, Mya arenaria, are fished commercially and recreationally across much of their distribution. Several management measures have been implemented in Atlantic Canada to regulate the clam fishery, including a minimum legal size limit of 50 mm. This legal size limit, however, is not based on contemporary data. A regional understanding of soft-shell clam reproductive biology in eastern New Brunswick is lacking, yet the management of this fishery would greatly benefit from this localized knowledge. As such, we collected soft-shell clams in Kouchibouguac National Park, New Brunswick, Canada, during the Spring, Summer and Fall of 2021, to assess size-at-maturity and time of spawning. Histology was used to determine the sex and maturity stage of individual soft-shell clams and maturity ogives were generated for female and male clams. Temporal changes in the gonadosomatic index (GSI) were also used to identify likely spawning times for female and male clams. Sex ratios were significantly unbalanced for most of the sites sampled, favouring females, with an overall sex ratio of 2.3:1 (F: M). Size-at-maturity was estimated at 39.7 mm and 40.7 mm for female and male soft-shell clams, respectively. Overall, GSI was higher in males, peaking in late May, declining sharply in June, and showing a more gradual decline from July until September. Female GSI also peaked in late May, but exhibited a continuous, gradual decline from mid-June through to September, suggesting that peak spawning likely occurred from late May to mid-June in 2021 but that some degree of spawning likely continued thereafter. Overall, these results provide insights into the reproductive biology of sub-legal sized soft-shell clams in eastern New Brunswick, providing managers with contemporary scientific information.

Temperature and winter duration requirements for reproductive success in johnny darter Etheostoma nigrum in the South Platte River basin, Colorado

Abstract Changes in water temperature and its seasonal timing influences the physiological processes of many aquatic ectotherms. Wastewater treatment plants (WWTP) contribute to warmer and more consistent water temperatures in streams draining the North American Great Plains, particularly during winter months. Reduced variation in seasonal water temperature may adversely affect fishes that rely on temperature fluctuation or specific overwintering temperatures for reproductive cues. We used johnny darter Etheostoma nigrum (Family Percidae), a thermally sensitive species native to the South Platte River Basin, as a focal species to assess the effects of winter water temperature regulations in Colorado. Our objective was to evaluate the effects of winter stream temperature and winter duration on reproductive success of johnny darter in the laboratory to inform development of water quality criteria for the South Platte River Basin. Winter duration (60, 90 or 120 days) and temperature (4 or 12°C) were crossed in a factorial design of six treatments that simulated warmed effluent‐impacted streams as well as streams with a more natural thermal regime. We defined reproductive success in johnny darter by examining four reproductive endpoints: (1) spawning timing, (2) egg and larvae production, (3) egg success, and (4) egg development. Across the four endpoints, seven main response variables were measured: spawning initiation date, eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, egg‐to‐larva survival and days to hatch. Winter temperature and duration influenced spawning timing and egg development. Earlier spawning initiation dates were observed in fish exposed to 12°C winters and was associated with a higher number of days to hatch. Eggs per gram of female per week, live larvae per gram of female per week, fertilisation success, hatching success, and egg‐to‐larva survival were similar among winter treatments. Although the State of Colorado chronic winter water temperature standard of 12°C appears to be adequate for egg and larvae production in johnny darter, our results showed that fish exposed to the standard began spawning significantly earlier than fish exposed to 4°C winters. Evaluating reproductive output in the context of seasonal timing is valid because spawning timing has the potential to affect overall production and egg development, and consequently recruitment and population sustainability. Therefore, spawning timing should be considered when making management decisions and revising water temperature standards. The warming of streams and rivers from WWTP effluent is a global issue, especially in areas that are undergoing rapid urbanisation. Fishes are particularly sensitive to water temperature and many fishes worldwide are likely to be experiencing changes in important physiological processes, affecting both reproduction and survival. Our study indicates that reproductive timing could be influenced by stream warming and stresses the need for further studies on the influence of anthropogenic effects on stream warming.

Global disruption of coral broadcast spawning associated with artificial light at night

Coral broadcast spawning events - in which gametes are released on certain nights predictably in relation to lunar cycles - are critical to the maintenance and recovery of coral reefs following mass mortality. Artificial light at night (ALAN) from coastal and offshore developments threatens coral reef health by masking natural light:dark cycles that synchronize broadcast spawning. Using a recently published atlas of underwater light pollution, we analyze a global dataset of 2135 spawning observations from the 21st century. For the majority of genera, corals exposed to light pollution are spawning between one and three days closer to the full moon compared to those on unlit reefs. ALAN possibly advances the trigger for spawning by creating a perceived period of minimum illuminance between sunset and moonrise on nights following the full moon. Advancing the timing of mass spawning could decrease the probability of gamete fertilization and survival, with clear implications for ecological processes involved in the resilience of reef systems.

Who spawns where? Temperature, elevation, and discharge differentially affect the distribution of breeding by six Pacific salmonids within a large river basin

Within the geographic range of salmonid fishes, many apparently suitable rivers and streams are used for reproduction by some species but not others. This is widely known but seldom addressed, as studies often examine factors determining the distribution of one or only a few species. We examined physical factors associated with the spawning distribution of six native Pacific salmonids (pink, chum, coho, and Chinook salmon, bull trout, and steelhead) in the Skagit River basin, Washington. Annual mean temperature and catchment elevation had the strongest association with spawning assemblage distribution, but stream length, annual discharge, seasonal hydrology, and land use were also influential. Some species (e.g., pink and Chinook salmon) were more closely associated with each other and with common variables than others, and bull trout were the most distinctive. For interpretation, we investigated the roles of adult body size, timing of spawning, and duration of juvenile rearing, but none of these factors explained groupings in the data. Interspecific differences in habitat association remained, suggesting fundamental constraints on species distributions with implications for conservation and restoration.

Verification of the Daily Periodicity of Microincrements Formation on the Otoliths of the Juvenilrs of the Ocellated Blenny &lt;i&gt;Opisthocentrus ocellatus&lt;/i&gt; (Stichaeidae) for a Retrospective Evaluation of the Period of Mass Hatching under the Conditions of Peter the Great Bay of the Japan Sea

Experiments were carried out on intravital otolith-tagging of juveniles of the ocellated blenny after transition to benthic life mode with Alizarin Red S. Marking at a dye concentration of 200 mg/L for 16–18 h at night, gave 100% formation of fluorescent marks with zero mortality of experimental individuals. Alizarin marks on the otoliths correspond to “stress” marks in the form of darker micro-increments, visible in transmitted light. The calculation of microincrements in the zone between two consecutive markings with an interval of 9 days confirmed the daily periodicity of their laying at this stage of development of the ocellated blenny. This allowed us to determine the period of hatching in natural conditions of juveniles in the Zhitkov Bay (Russky Island, the Peter the Great Bay, Japan sea). Hatching of larvae in 2017 in this species occurred, according to our estimates, from the last decade of March to the end of the second decade of April, with a peak in the first decade of April. Hatching begins even under the ice at a slightly negative water temperature of –1–0°C, but it proceeds mainly already at a temperature of 1–3°C, after the removal of ice from the bay. Taking into account the known timing of spawning of the ocellated blenny in the Peter the Great Bay (November–early December), we can state that the development of its eggs in this area is greatly slowed down at water temperatures below zero in December–March and can go on for 4–5 months, which is almost 3 times longer than the development time in more mild conditions of the south Hokkaido.

Effects of cadmium exposure during the breeding period on development and reproductive functions in rare minnow (Gobiocypris rarus).

Cadmium is a common reproductive toxin in aquatic systems. Cd exposure of fish species at high concentrations can severely affect the reproductive function of fish. However, the underlying toxicity of cadmium exposure at low concentrations on the reproductive function in parental fish remains unclear. To investigate the impacts of cadmium exposure on reproductive capability, eighty-one male and eighty-one female rare minnows (Gobiocypris rarus) were exposed to cadmium at 0 (control group), 5 and 10μg/L for 28days, and then transferred into clean water to pair spawn. The results showed that cadmium exposure at 5 or 10μg/L for 28days in rare minnows could reduce the success rates of pair spawning in parent rare minnows, lessen no-spawning activities, and prolong the time for first spawning. Furthermore, the mean egg production of the cadmium exposure group increased. The fertility rate of the control group was significantly higher than that of the 5μg/L cadmium exposure group. Anatomical and histological data further revealed that the intensity of atretic vitellogenic follicles significantly increased and spermatozoa vacuolated after cadmium exposure (p < 0.05), but slightly increased the condition factor (CF), and relatively stable gonadosomatic index (GSI) values were also observed in the cadmium exposure groups. These observed results indicated that cadmium exposure at 5 or 10μg/L affected the reproductive activity of paired rare minnow by accumulating Cd in the gonads, and the effect diminished over time. The reproductive risk of low-dose cadmium exposure to fish species remains a cause for concern.

Parental exposure to polystyrene nanoplastics and di(2-ethylhexyl) phthalate induces transgenerational growth and reproductive impairments through bioaccumulation in Daphnia magna

The ubiquitous presence of polystyrene nanoplastics (PSNPs) and di(2-ethylhexyl) phthalate (DEHP) in the aquatic environment may cause unpredictable negative effects on aquatic organisms and even continue to the offspring. This study assessed the transgenerational impacts of parental exposure to PSNPs and DEHP over four generations (F0–F3) of Daphnia magna. A total of 480 D. magna larvae (F0, 24 h old) were divided into four groups with six replicates (each of them contains 20 D. magna) and exposed with dechlorinated tap water (control), 1 mg/L PSNPs, 1 μg/L DEHP, and 1 mg/L PSNPs + 1 μg/L DEHP (PSNPs-DEHP) until spawning begins. Subsequent to exposure, all the surviving F1 offspring were transferred to new water and continued to be cultured until the end of F3 generation births in all groups. The results showed that the PSNPs accumulated in F0 generation and were inherited into F1 and F2 generations, and disappeared in F3 generation in PSNPs and PSNPs-DEHP groups. However, the accumulation of DEHP lasted from F0 generation to F3 generation, despite a significant decline in F2 and F3 generations in DEHP and PSNPs-DEHP groups. The accumulation of PSNPs and DEHP caused overproduction of reactive oxygen species in F0–F2 generations and fat deposition in F0–F3 generations. Additionally, single and in combination parental exposure to PSNPs and DEHP induced regulation of growth-related genes (cyp18a1, cut, sod and cht3) and reproduction-related genes (hr3, ftz-f1, vtg and ecr) in F0–F3 generations. Survival rates were decreased in F0–F1 generations and recovered in F2 generation in all treatment groups. Furthermore, the spawning time was prolonged and the average number of offspring was increased in F1–F2 generaions as a defense mechanism against population mortality. This study fosters a greater comprehension of the transgenerational and reproductive effects and associated molecular mechanisms in D. magna.