Female Spawning Research Articles

Reproductive performance of lumpfish (Cyclopterus lumpus, L. 1758) females: Effects of integrated photoperiod and temperature manipulations on sexual maturation and spawning.

A successful control of sexual maturation is crucial for year-round production of lumpfish juveniles destined as cleaner fish in Atlantic salmon aquaculture. This study investigated the combined effects of photoperiod and temperature manipulations on sexual maturation and spawning in lumpfish females. Lumpfish juveniles were exposed to simulated natural and nine-month compressed annual photoperiods, with subsequent temperature elevation. Body weight (BW), condition factor (K), gonadosomatic index (GSI), ovarian development, plasma levels of 17β-estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT), and spawning were assessed. Compressing the natural photoperiod caused a clear increase and decrease in GSI, T, 11-KT and E2 towards and during the spawning period. Before the temperature elevation, GSI, T, 11-KT, E2 and ovarian development were advanced in the compressed photoperiod. After the temperature elevation, GSI, T, 11-KT and E2 fluctuated more in the compressed photoperiod, while in the natural photoperiod, E2 declined, and GSI, T and 11-KT increased. Spawning was advanced by 1 month in the compressed photoperiod compared to the natural photoperiod. Temperature elevation led to higher levels, earlier peaks and declines of T, 11-KT or E2 in both photoperiods, and advanced spawning by 1.5 months in the compressed photoperiod compared to the natural photoperiod. Temperature elevation also led to increased ovulation recruitment and increased cumulative weight of spawned eggs in the natural photoperiod. Compressing the natural photoperiod and elevating temperature can thus advance sexual maturation and spawning in lumpfish females. Due to the lower amounts of spawned egg weights in the high temperature compressed photoperiod, further studies on effects of photoperiod and timing of temperature manipulations on spawning, fecundity and egg quality could optimize the photothermal manipulations on lumpfish broodstock.

Genetic Diversity Losses in Mantis Shrimp Oratosquilla oratoria Offspring Created for Supportive Releases Using an Ecological Breeding in Earthen Pond Method

ABSTRACTArtificial breeding of mantis shrimp Oratosquilla oratoria, using the ecological breeding in earthen pond (EBEP) method, has been carrying out from 2019, and the produced larvae have always been used for supportive breeding programs in Bohai Bay. To assess the degree of fidelity of enhancement programs used an EBEP method to native genetic pools, genetic diversity at 10 microsatellite loci was analyzed in three hatchery offspring populations, their wild parent stocks, and their wild contemporaneous offspring. Significant decrease in the almost genetic diversity parameters and highly significant differences in shannon's information index (decreasing by 22.54%–40.97%) and allelic richness (33.80%–46.87%) were observed between in hatchery populations. This further created relatively more genetic differentiation between the hatchery and wild population, as the pairwise Fst values and genetic distances showed. The mean pairwise relatedness coefficients showed higher values within hatchery populations and lower values within wild populations. Hatchery populations contained the fewest full‐sib families and offspring were extremely distributed in 10–11 full‐sib groups in each hatchery population. The relatively small number of actual spawning females and large variance in parental contribution to the next generation possibly causes allele reduction in the hatchery population, which in turn leads to a decrease in allelic diversity and an increase in genetic similarities among individuals. Promoting synchrony of ovarian development in females, providing good conditions for incubation and larvae culture and balancing the contributions of parents will be important in future breeding propagation.

Характеристика маточного стада несвицького внутрішньопородного типу українських рамчастої та лускатої порід коропа за комплексом продуктивних та репродуктивних показників

Purpose. To provide an assessment of the complex of productive and reproductive parameters of the brood stock of the Nesvych intrabreed type of Ukrainian framed and scaly breeds of carp grown in pond conditions of the Polissia zone. Methodology. The study was conducted at fish farms of Lviv and Volyn regions of Ukraine during 2004-2024. The material for the study was sexually mature carps of the Nesvych type of different ages. The main fish productive and biological parameters were studied during spring valuation according to generally accepted methods in fish farming. Exterior evaluation was carried out according to weight and the main parameters of body structure. Measurements were made with a centimeter tape with an accuracy of 1 mm. Individual weighing of older age groups was carried out on electronic scales PROK VT-150-R1, juveniles - TS-500. Based on the results of the measurements, the main exterior parameters were analyzed and determined — girth, body length to height ratio, head length. The ejaculate volume was determined using an Eppendorf pipette-dispenser with an accuracy of 0.1 cm3. Sperm movement activity was determined using a Zeiss Axiostar plus microscope with a 20x/0.40 phase-contrast objective. The number of spermatozoa in cm3 was calculated using a Macler camera. Calculation of the absolute working fertility was carried out by the weight method, with the calculation of the number of eggs in 1 g and the subsequent determination of the weight of 1 egg. Relative working fertility was defined as the ratio of working fertility to body weight. Findings. The study showed that carps of the Nesvych intrabreed type had exterior parametetrs typical for Ukrainian carp breeds. At the same time, the working fertility of first-time spawning females was in the range of 328.1 - 522.7 thousand eggs, age 6-8 females - 645.7 - 1178.3 thousand eggs, older age groups - 536.2 – 1014.0 thousand eggs. With the average ejaculate volume of 7.6 – 8.3 cm3 in first-spawning males and re-spawning ones 14.9 – 21.3 cm3, active movement of spermatozoa after their activation was observed: 33.1 – 48.6 s and 56.3 - 59.3 s, respectively. At the same time, the working fertility of males was 90.1 - 443.2 billion spermatozoa. The positive response of female Nesvych carp to pituitary stimulation exceeded 95%. Originality. The results of 20 years of selective-breeding work with a representative of aquaculture in the western region of Ukraine are highlighted. In particular, weight dynamics, main exterior and reproductive parameters of brood fish of different ages of brood carp stock of Nesvych intrabreed type of Ukrainian framed and scaly breeds, which were presented and successfully passed the state approval in 2023, are summarized. Practical value. High fish productive and biological parameters of broodstocks of the Nesvych inbred type allow recommending them for use for the purpose of commercial cultivation. Key words: Nesvych carp, intrabreed type, brood stock, exterior, weight, age groups, condition factor fertility, ejaculate volume.

Male lake char release taurocholic acid as part of a mating pheromone.

The evolutionary origins of sexual preferences for chemical signals remain poorly understood, due, in part, to scant information on the molecules involved. In the current study, we identified a male pheromone in lake char (Salvelinus namaycush) to evaluate the hypothesis that it exploits a non-sexual preference for juvenile odour. In anadromous char species, the odour of stream-resident juveniles guides migratory adults into spawning streams. Lake char are also attracted to juvenile odour but have lost the anadromous phenotype and spawn on nearshore reefs, where juvenile odour does not persist long enough to act as a cue for spawning site selection by adults. Previous behavioural data raised the possibility that males release a pheromone that includes components of juvenile odour. Using metabolomics, we found that the most abundant molecule released by males was also released by juveniles but not females. Tandem mass spectrometry and nuclear magnetic resonance were used to identify the molecule as taurocholic acid (TCA), which was previously implicated as a component of juvenile odour. Additional chemical analyses revealed that males release TCA at high rates via their urine during the spawning season. Finally, picomolar concentrations of TCA attracted pre-spawning and spawning females but not males. Taken together, our results indicate that male lake char release TCA as a mating pheromone and support the hypothesis that the pheromone is a partial match of juvenile odour.

Life-cycle modeling reveals high recovery potential of at-risk wild Chinook salmon via improved migrant survival

Chinook salmon ( Oncorhynchus tshawytscha) in the Columbia River basin are threatened by anthropogenic changes to migratory corridors, estuaries, and natal habitats. Streams provide spatially heterogeneous natal habitats essential for salmon spawning and rearing life stages. We fit a statistical state-space model to salmon populations in Idaho's Middle Fork Salmon River (MFSR) to assess spatial variation in natal productivity and population growth. Our model integrated multiple long-term data sets to estimate variation in per-capita smolt production and smolt-to-adult (SAR) survival. Smolt production varied across stream segments, averaging 104.48 female smolts per spawning female, while SARs averaged 0.74%. Chinook salmon population growth rates exceeded replacement in 17% of segments (4 of 23). By increasing SARs to 1.8% (near the lower bound of Columbia River basin recovery targets), we predict that all 23 MFSR segments will yield positive population growth rates at contemporary (very low) spawner densities. Our analysis suggests that for Snake River basin populations within high-quality natal habitats, SAR improvements will elevate salmon population growth rates and enhance restoration of at-risk wild Chinook salmon.

Reproductive biology of the introduced red-swamp crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae) in western Japan

Abstract The red swamp crayfish Procambarus clarkii (Girard, 1852) has been responsible for negative impacts on native benthic fauna and flora in invaded freshwater ecosystems around the world, including Japan. We need to clarify the reproductive biology in the invaded habitats as basic information to effectively control the introduced populations, but the reproductive biology of P. clarkii in Japan (especially in western Japan) has not been well studied. We conducted monthly samplings of P. clarkii from November 2015 to November 2016 in a pond (which does not freeze, even in winter) in Okayama, western Japan, both by using shrimp cage traps and by hand nets to examine aspects of the reproduction, including a form alternation (i.e., Form I and II). We also reared spawning females in the laboratory and calculated the accumulated water temperature during the period to Stage-3 juveniles after spawning. The total number of individuals caught throughout the study period was 6,319 (2,601 males and 2,777 females, with eight of unknown sex and 933 juveniles). The males were all Form I with a breeding status from September to November 2016. We first found ovigerous females in July 2016 and females carrying hatchlings in October 2016, even in January 2016. The form alternation in males was confirmed not only in the cheliped length, but in the hook length. In laboratory observations, approximately 52 days with approximately 1,222 °C degree-days of the accumulated water temperature were necessary to Stage-3 juveniles after spawning. Our results indicate that P. clarkii can reproduce within approximately five months of hatching.

Морфофизиологические и биохимические исследования каспийской атерины (Atherina boyeri caspia Risso, 1810)

The article highlights physiological and biochemical parameters of atherina (Atherina boyeri caspia Risso, 1810) in the Middle Caspian Sea at various stages of the annual cycle. The state of the fish organism was studied in the period from February to October 2022, which characterized the pre-spawning, spawning and feeding periods. The size-weight and age parameters of atherina were determined. The concentration of the main reserve substances of the fish body - total lipids and water-soluble protein – was analyzed in the muscles of the atherina. In the pre-spawning period and at the beginning of spawning of females, the level of morphological changes in the gonads was studied. There were no found significant differences in the content of total lipids and water-soluble protein in the muscles of males and females. Patterns of changes in the amount of muscle water-soluble proteins and total lipids were recorded in the entire sample of the Caspian atherina during the pre-spawning period and at the beginning of spawning. This is typical for portioned spawning fish, in which the energy expenditure of the body is directed to the formation, maturation of gonads, the removal of sexual products and the maturation of the next portions during the spawning period. In September-October, that is, already at the stage of feeding, a multidirectional character in lipid and protein metabolism was noted in the body of atherina. According to the results of histological examination, the beginning of spawning in atherina was noted in April. Mature oocytes with resorption at an average level of 30-31% were recorded in the ovaries of portioned spawning atherina in February-April, which characterized the adaptive mechanisms of the organism in the conditions of this habitat. In September, there was a significantly positive (p < 0.05) statistical correlation between the concentration of total muscle lipids and the mass of fish (r = +0.47), which characterized a positive energy balance in the body, so necessary for the next stages of life.

Loss of the adaptor protein Sh3bgrl initiates ovarian fibrosis in zebrafish.

Ovarian fibrosis is a reproduction obstacle leading to female infertility in vertebrates, but the cause underlying the cellular events is unclear. Here, we found that the small adaptor protein SH3-domain-binding glutamate-rich protein like (Sh3bgrl) plays an important role in female reproduction in zebrafish. Two sh3bgrl mutant alleles that result in sh3bgrl depletion contributes to female spawning inability. Comparative transcriptome analysis revealed that sh3bgrl knockout mechanistically causes the upregulation of genes associated with extracellular matrix (ECM) and fiber generation in the zebrafish ovary. Consequently, extra ECM or fibers accumulate and are deposited in the ovary, resulting in eventual spawning inability. Our findings thus provide insights into understanding the underlying mechanism of infertility by ovarian fibrosis and provide a novel and valuable model to study female reproduction abnormality.

Female reproductive fluid concentrations affect sperm performance of alternative male phenotypes in an external fertilizer.

There is growing evidence that the female reproductive fluid (FRF) plays an important role in cryptic female choice through its differential effect on the performance of sperm from different males. In a natural spawning event, the male(s) may release ejaculate closer or further away from the spawning female. If the relative spatial proximity of competing males reflects the female pre-mating preference towards those males, then favoured males will encounter higher concentrations of FRF than unpreferred males. Despite this being a common situation in many external fertilizers, whether different concentrations of FRF can differentially influence the sperm performance of distinct male phenotypes (favoured and unfavoured by the female) remains to be elucidated. Here, we tested this hypothesis using the grass goby (Zosterisessor ophiocephalus), a fish with distinct territorial-sneaker reproductive tactics and female pre-mating preference towards territorial males, that consequently mate in an advantaged position and whose sperm experience higher concentrations of FRF. Our findings revealed a differential concentration-dependent effect of FRF over sneaker and territorial sperm motility only at low concentrations (i.e. at the distance where sneakers typically ejaculate), with increasing FRF concentrations (i.e. close to the eggs) similarly boosting the sperm performance of both sneaker and territorial males. The ability to release sperm close to the eggs is a prerogative of territorials, but FRF can likewise advantage the sperm of those sneakers that are able to get closer, allowing flexibility in the direction of female post-mating choice.

Reproductive behavior of Atlantic halibut (Hippoglossus hippoglossus) interpreted from electronic tags.

Reproductive timing, location, and behavior are important characteristics that determine marine population dynamics, structure, and resilience to threats, including fishing and climate change. It is challenging to evaluate factors driving variability in these reproductive traits in wild fishes because of the difficulty observing individuals in their natural environments. In the present study, we used high-resolution depth, temperature, and acceleration time series recorded by pop-up satellite archival tags to (1) identify and characterize patterns in depth and acceleration that may be indicative of spawning events in large Atlantic halibut (Hippoglossus hippoglossus), and (2) estimate the effects of individual traits (body size and sex) and environmental factors (location and temperature) on spawning time and frequency. Unique rapid rises observed in the winter depth profiles were interpreted as spawning events. The initiation of the first presumed spawning rise was negatively correlated to water temperature experienced during the prespawning season, suggesting that currently increasing water temperature in the Gulf of St. Lawrence may induce phenological change in halibut spawning time. The number of rises of batch-spawning females was unrelated to female body size. The present study demonstrates how electronic tagging can be used for in-depth characterization of timing, location, and behaviors associated with spawning in a large flatfish species. Such information can inform spatiotemporal management and conservation measures aiming to protect species from directed fishing and by-catch during spawning.

Reproductive biology of wahoo (Acanthocybium solandri) in the Canary Islands (eastern-central Atlantic)

The reproductive status of wahoo (Acanthocybium solandri) in the eastern-central Atlantic was investigated to better understand their migration and breeding patterns. The waters around the Canary Islands are considered a breeding area for wahoo; and this study documents the first described breeding activity found in the eastern Atlantic. The presence of many mature and spawning capable wahoo reported in this study confirms its spawning activity in this region. Off the Canary Islands, only mature individuals spawn in the region where no immature individuals were observed to date. Most of the specimens captured in Canary Islands waters exceed 100 cm TL (about 2 years old). Values of the gonadosomatic index (GSI) of males were much lower than those estimated for females. Testes showed little changes in size throughout gametogenesis, while ovaries increased significantly (p<0.05). The low values make it inadvisable to use GSI in males to determine spawning activity. In the Canary Islands, wahoo females spawn (fishes with tertiary vitellogenic oocytes, postovulatory follicles or germinal vesicle migration, yolk coalescence, germinal vesicle breakdown and hydrated oocyte) mainly during a 4-month period in summer. Both females of spawning capable outside the main summer breeding period and females in regressing phase during the spawning period have been observed in the Canary Islands. Males were found in the spawning capable phase throughout the year, with greater prevalence between May and October.

The effects of short neuropeptide F on ovarian maturation and spawning in female giant freshwater prawn, Macrobrachium rosenbergii, and associated regulatory mechanisms

In the present study, we investigated the effects of two short neuropeptide F (Mro-sNPF) mature sequences, namely APALRLRFamide and DRTPALRLRFamide, on ovarian maturation and spawning in Macrobrachium rosenbergii females. At doses of 10−5 and 10−6 mol/prawn, both Mro-sNPF peptides significantly shortened the ovarian developmental period (P < 0.05), but enhanced the gonadosomatic index (GSI), oocyte diameter (OD), and cell proliferation, compared with control values (P < 0.05). However, at the lowest dose (10−7 mol/prawn), neither peptide significantly affected ovarian maturation, GSI, nor OD compared with the control values. Females treated with the two peptides at the dose of 10−5 or 10−6 mol/prawn attained mature oocyte stages faster than did control females. Treatment with both peptides significantly elevated hemolymph vitellogenin concentrations and upregulated MrEcR transcripts, compared with the control treatment (P < 0.05). Finally, both Mro-sNPFs induced spawning by shortening its duration by half (∼1.5 days) compared with the control duration (∼3.1 days) (P < 0.05). The number of eggs per spawn was approximately 15.4 × 104 eggs in the experimental group and in the control group (∼15.35 × 104 eggs), albeit without significance. Therefore, among the treatment groups, using APALRLRFamide at 10−5 mol/prawn showed promising effects on the induction of ovarian maturation and spawning. Taken together, Mro-sNPF peptides can promote ovarian development and spawning, indicating their potential application to stimulate gamete and larval production in this important crustacean aquaculture species.

Genomic basis of Y-linked dwarfism in cichlids pursuing alternative reproductive tactics.

Sexually antagonistic selection, which favours different optima in males and females, is predicted to play an important role in the evolution of sex chromosomes. Body size is a sexually antagonistic trait in the shell-brooding cichlid fish Lamprologous callipterus, as "bourgeois" males must be large enough to carry empty snail shells to build nests whereas females must be small enough to fit into shells for breeding. In this species, there is also a second male morph: smaller "dwarf" males employ an alternative reproductive strategy by wriggling past spawning females into shells to fertilize eggs. L.callipterus male morphology is passed strictly from father to son, suggesting Y-linkage. However, sex chromosomes had not been previously identified in this species, and the genomic basis of size dimorphism was unknown. Here we used whole-genome sequencing to identify a 2.4-Mb sex-linked region on scaffold_23 with reduced coverage and single nucleotide polymorphism density in both male morphs compared to females. Within this sex region, distinct Y-haplotypes delineate the two male morphs, and candidate genes for body size (GHRHR, a known dwarfism gene) and sex determination (ADCYAP1R1) are in high linkage disequilibrium. Because differences in body size between females and males are under strong selection in L.callipterus, we hypothesize that sexual antagonism over body size initiated early events in sex chromosome evolution, followed by Y divergence to give rise to bourgeois and dwarf male reproductive strategies. Our results are consistent with the hypothesis that sexually antagonistic traits should be linked to young sex chromosomes.

Reproductive and Developmental Alterations on Zebrafish (Danio rerio) Upon Long-Term Exposure of Di-ethyl phthalate (DEP), Di-isononyl phthalate (DINP) and Di (2-ethylhexyl) phthalate (DEHP)

Di (2-ethylhexyl) phthalate (DEHP), di-ethyl phthalate (DEP) and di-isononyl phthalate (DINP) are all endocrine disrupting chemicals (EDCs) for organisms. However, little research has been done on the effects of long-term EDC exposure. The present study found that the zebrafish barely grew during the 7months of DINP exposure. The fecundity rate (%) of female spawning was lower in the DEHP treatment by 4months compared to other exposure groups. Zebrafish treated with 12.5-25.0ppm of DEP for 4months presented no spawning. Gonadal-somatic index (GSI) levels significantly decreased, and there were more oocytes in the atresia and peri-nucleus stage compared to the control group. In addition, the hatching rate of embryos were 71.02%, 56.92%, and 21.70% for females treated with DINP, DEHP and DEP, respectively. There were also abnormal craniofacial chondrogenesis development on 72hpf embryos upon females treated with the three EDCs. In conclusion, long term exposure of DEHP, DINP, and DEP did not only affect the reproductive capacity of female zebrafish, but the 3 plasticizers also influence craniofacial cartilage development of its offspring.

Catchment-scale stream network spatio-temporal models, applied to the freshwater stages of a diadromous fish species, longfin eel (Anguilla dieffenbachii)

Spatio-temporal modelling frameworks are important tools for evaluating changes in the population structure of freshwater species, to inform population assessments. However, in the stream networks occupied by freshwater species, two data points in space are more related by physical connectivity than by straight-line, Euclidian distance. Therefore, there is a need for spatio-temporal modelling frameworks that represent the relatedness of points based on physical connectivity. We developed such a modelling framework, known as the “VAST stream network modelling framework", using the widely-employed vector autoregressive spatio-temporal modelling platform VAST and the Ornstein-Uhlenbeck process for spatial variance. Here, we demonstrate the VAST stream network spatio-temporal modelling platform with two applications to the freshwater stages of a diadromous fish species, the endemic New Zealand longfin eel (Anguilla dieffenbachii), and a simulation experiment. The first real-world application considers a single category (longfin eel) and models its probability of encounter in the Waitaki catchment, while the second distinguishes between two categories (smaller and larger longfin eels) and models their numerical densities in the greater Waikato region. These two applications demonstrate how stream network spatio-temporal models can usefully inform freshwater resource managers, providing insights into changes in fish encounter probability and density for different fish length classes and estimates of effective river length occupied. The simulation experiment uses the Waikato model as an operating model to evaluate alternative sampling scenarios for accuracy, precision and coverage, to advise on data requirements. A yearly sample size of 30 sites over a 20-year time series had the greatest precision and accuracy in trend estimates among all scenarios investigated. We also found that, for the scenario with declining female spawning biomass, increasing the yearly sample size from 15 sites to 30 sites in a 9-year time series increased the precision and resulted in unbiased estimates. There is a need to optimise sampling schemes for the freshwater stages of diadromous species, including longfin eel, and we, therefore, recommend further simulation experiments to explore scenarios of population trends, habitat features and sampling approaches.

Twice-annually spawning of rainbow trout females in recirculation sistems

During the evaluation of broodstocks on the basis of the Federal Fish Breeding Genetic Center (FSGTSR), rainbow trout females maturing with an interval of 6 months were found. It has been established that under conditions of RAS, females with bicyclic spawning can produce the same full-fledged reproductive products of high fish-breeding quality, as well as producers with a normal sexual cycle. It has been suggested that maturation every six months of only a part of females indicates the genetic predetermination of individual fish to the appearance of this feature. The breeding of domestic breeds of rainbow trout with bicyclic spawning will also greatly contribute to the realization of the biological potential of this species and open up new prospects for trout breeding in Russia.

Life Cycle Exposure to Cyhalofop-Butyl Induced Reproductive Toxicity in Zebrafish.

Cyhalofop-butyl (CyB) is a herbicide widely used in paddy fields that may transfer to aquatic ecosystems and cause harm to aquatic organisms. In this study, zebrafish (Danio rerio) were exposed to CyB at environmental concentrations (0.1, 1 and 10 µg/L) throughout their adult life cycle, from embryo to sexual maturity. The effects of CyB on zebrafish growth and reproduction were studied. It was found that female spawning was inhibited, and adult male fertility decreased. In addition, we examined the expression of sex steroid hormones and genes related to the hypothalamus–pituitary–gonad–liver (HPGL) axis. After 150 days of exposure, the hormone balance in zebrafish was disturbed, and the concentrations of 17β-estradiol (E2) and vitellogenin (VTG) were decreased. Changes in sex hormone were regulated by the expression of genes related to the HPGL axis. These results confirmed that long-term exposure to CyB at environmental concentrations can damage the reproductive capacity of zebrafish by disrupting the transcription of genes related to the HPGL axis. Overall, these data may provide a new understanding of the reproductive toxicity of long-term exposure to CyB in zebrafish parents and offspring.

Strategy of spawning in the tropical squid Lolliguncula diomedeae females: allocation of energy, senescence, and influence of Aggregata coccidians

Although the squid Lolliguncula diomedeae (Hoyle, 1904) is of commercial and ecological importance in the Gulf of Tehuantepec (southeastern Mexico), this is the first study to examine female spawning strategy. Information on reproductive indicators was used to assess the impact of spawning behavior on growth rates and the condition of somatic tissue, since energy for reproduction is derived mainly from somatic tissue and consumed food. Additionally, oocyte storage patterns were examined to determine the type of spawning that characterizes this species. A total of 1347 females, ranging between 27.3 and 90.0 mm dorsal mantle length (ML) and 0.1 and 25.6 g of total weight, were examined. Statolith analysis indicates that the life cycle of L. diomedeae is 212 days. Allometric growth was observed during the female life cycle. The size at maturity was 68.54 mm ML, with synchronous ovulation (by groups) and intermittent spawning. The results showed that L. diomedeae is an energetically efficient squid species that feeds during all of its reproductive life stages, thus ensuring the occurrence of partial spawning events, and that feeding ends when senescence begins. However, its life cycle could be affected by the presence of coccidian parasites, mainly during senescence.

Transcriptomic Profiling Revealed Signaling Pathways Associated with the Spawning of Female Zebrafish under Cold Stress

As one of the critical abiotic factors, temperature controls fish development and reproduction. However, the effects of low temperature on the transcriptional regulation of zebrafish reproduction remain largely unclear. In this study, the fecundity of zebrafish was examined after exposure to cold temperatures at 19.5 °C, 19 °C, 18.5 °C, or 18 °C. The temperature at 19 °C showed no significant influence on the fecundity of zebrafish, but temperature at 18.5 °C or 18 °C significantly blocked the spawning of females, suggesting the existence of a low temperature critical point for the spawning of zebrafish females. Based on these observations, the brains of anesthetized fish under cold stress at different cold temperatures were collected for high-throughput RNA-seq assays. Key genes, hub pathways and important biological processes responding to cold temperatures during the spawning of zebrafish were identified through bioinformatic analysis. The number of down-regulated and up-regulated genes during the temperature reduction from egg-spawning temperatures at 19.5 °C and 19 °C to non-spawning temperatures at 18.5 °C and 18 °C were 2588 and 2527 (fold change ≥ 1.5 and p-value ≤ 0.01), respectively. Venn analysis was performed to identify up- and down-regulated key genes. KEGG enrichment analysis indicated that the hub pathways overrepresented among down-regulated key genes included the GnRH signaling pathway, vascular smooth muscle contraction, C-type lectin receptor signaling pathway, phosphatidylinositol signaling system and insulin signaling pathway. GO enrichment analysis of down-regulated key genes revealed the most important biological processes inhibited under non-spawning temperatures at 18.5 °C and 18 °C were photoreceptor cell outer segment organization, circadian regulation of gene expression and photoreceptor cell maintenance. Furthermore, 99 hormone-related genes were found in the brain tissues of non-spawning and spawning groups, and GnRH signaling pathway and insulin signaling pathway were enriched from down-regulated genes related to hormones at 18.5 °C and 18 °C. Thus, these findings uncovered crucial hormone-related genes and signaling pathways controlling the spawning of female zebrafish under cold stress.

AGE DYNAMICS OF REPRODUCTIVE ABILITY AND QUALITY OF AFRICAN CATFISH OFFSPRING UNDER AQUACULTURE CONDITIONS

The work is devoted to study of influence of African catfish age on reproductive ability and viability of its offspring. The problem is relevant, since the issues of age selection of producers have developed relatively recently in industrial aquaculture and have not been enough studied yet. As for practical fish farming, specialists often face the problem of low quality of fish gametes that are too young or old enough. The aim of the study was a comparative assessment of the age-related variability of reproductive ability and viability of African catfish offspring. African catfish breeders at the age of 12, 24, 48, 60 months were selected for the research, four experimental groups were formed. The parameters of fertility and the quality of reproductive products, linear and weight growth of the offspring, as well as its viability were studied. The results of the study showed age-related changes in the quality of reproductive products, embryos developing from them, and subsequent larvae. Differences in egg fertility, viability of embryos and larvae, and the size of larvae obtained from producers of different ages were established. All parameters indicate that the parents’ age significantly affects the quality of their offspring. As for study of reproductive products of female African catfish of different ages by a number of parameters, such as size and diameter of eggs, certain differences were established in morphometric and physiological parameters of eggs and sperm. The study of the effect of parental age on offspring survival rate in embryonic and postembryonic periods showed that the offspring survival rate of first spawning females was the lowest and increased as the parental individuals matured. The viability of offspring in middle-aged groups of breeders was the highest.