Female Fish Research Articles

Seasonal variations of vitamins A, E and carotenoids in eelpout (Zoarces viviparus) from a Danish fjord, in relation to reproductive cycle

Retinoids (vitamin A) and tocopherols (vitamin E) are essential for key biological functions in vertebrates, including cell growth, cell death and differentiation, embryonic development, reproduction and vision. In fish, however, much less is known about the retinoid functions, although retinoic acid has been shown to be involved in embryonic development. In this study, we quantified the levels of different retinoids, carotenoids and vitamin E in various tissues of both adult and embryos of the viviparous fish eelpout (Zoarces viviparus). Our results demonstrate clear seasonal differences in the levels of these vitamins in the liver of the female fish as well as in its ovarian tissues, eggs and/or embryos. Overall, this study is a baseline assessment and describes the annual variations in the vitamin status by comparing the tissue distribution of retinoids, carotenoids and vitamin E. This baseline study investigates the natural background levels of these compounds and relates their seasonal fluctuations to the reproductive cycle in the viviparous eelpout. The results of this study strengthen the current evidence base necessary to understand retinoid pathways during fish development. This understanding is crucial for utilizing retinoid composition in fish as a biological response to exposure to environmental pollution with hazardous substances in the marine environment.

Effect of Microplastic Exposure to the Reproductive Energy and Fecundity of Female Wami Tilapia (Oreochromis urolepis, Norman 1922) Fish

ABSTRACTThere is mounting evidence indicating that microplastics (MPs, < 5 mm) cause reproductive dysfunction in fish, yet information on the long‐term effects of MP exposure remains scarce. In this study, Wami tilapia fries were exposed to 38–45 µm polyethylene (PE) MPs for their first 2 months in treatment groups of control (0 PE MPs/mL), 1, 10, and 100 PE MPs/mL (with 60 individuals per group in triplicates), and subsequently maintained in a ratio of 3 females to 1 male for an additional 5 months. Reproductive proxies and parameters of female fish health were calculated, and models were developed according to the Akaike information criterion (AIC) and no significant differences in fecundity, relative fecundity, hepatosomatic index (HSI), weight, length, gonadosomatic index, and oocyte packing density were found between treatment groups (one‐Way ANOVA, p > 0.05). However, condition factors varied significantly between treatment groups (Kruskal–Wallis Test, p = 0.006), with the control group differing significantly from the groups exposed to 1 PE MPs/mL (p = 0.007), 10 PE MPs/mL (p = 0.03), and 100 PE MPs/mL (p = 0.001). Fecundity showed strong correlations with weight and length in all treatment groups except the group exposed to 10 PE MPs/mL (weight: r = 0.471, p = 0.346; length: r = 0.688, p = 0.131) and showed insignificant correlations with condition factors and HSI. Multiple regression models revealed that weight significantly contributed to fecundity in all treatment groups except the group exposed to 10 PE MPs/mL. Histopathological analysis indicated damage to livers and small intestines proportional to the dose of PE MPs. This study demonstrates that long‐term exposure of fish to MPs has no significant effect on fecundity but impairs fish health, which could potentially jeopardize the quality of fish eggs and recruitment.

Ultrasonography for non-invasive sex identification and reproductive assessment in Nile tilapia (Oreochromis niloticus).

Sex identification and the selection of monosex male tilapia are crucial for tilapia aquaculture. In this study, we evaluated the application of ultrasonography as an alternative procedure for sex identification and reproductive assessment in Nile tilapia (Oreochromis niloticus). Ultrasonography was performed on 23 fish weighing 232-1,281 g to capture longitudinal and transverse images of the ovaries and testes. Female tilapia were identified by the presence of numerous small egg granules and gray or light gray ovarian tissue and male tilapia by the homogeneous echogenicity and uniform gray tubular appearance of the testes. These distinct echogenic patterns allowed for accurate differentiation between the female and male fish. Ultrasonography achieved a 95% accuracy in sex identification, with minimal stress to the fish during the procedure, compared to manual sex sorting, which demonstrated an accuracy of 87%. Furthermore, the method facilitated the assessment of the reproductive status of the fish, including the maturation stages and fecundity potential. The use of ultrasonography offers significant advantages over traditional methods, such as animal welfare enhancements and improved breeding program efficiency. Our findings support the integration of ultrasonography into aquaculture practices and will promote sustainable and humane fish farming while optimizing reproductive management and productivity.

Biochemical analysis and fertilization success of Cirrhinus mrigala ova during induced spawning

Fish egg quality is very crucial in aquaculture sector for production of healthy seed. Egg yolk is an energy reservoir for growth and development of embryo. This study evaluated the biochemical composition and quality of Cirrhinus mrigala eggs at three different hatchery sites of Pakistan, (Site 1= Fish Seed Hatchery, District Pakpattan; Site 2= Sidhuwan Hatchery, Head Balloki, District Kasur; Site 3= Chenab Fish Hatchery, Rangpur, District Muzaffargarh) during induced breeding. For this, a total of 36 (18 males and 18 females) fish brooders, 12 (06 males and 06 females) from each site were utilized. Fatty acids analysis revealed significant differences among three different sites. Saturated fatty acids i.e., palmitic acid (C16:0) and stearic acids (C18:0) were higher at site 2 compared to the others sites. Monounsaturated fatty acids i.e., Oleic acid (C18:1) and polyunsaturated fatty acids i.e., Docosahexaenoic acid (DHA) (C22:6) exhibited considerably greater values at site 2 than those of other two sites. Egg mineral contents unveiled remarkable differences, particularly at site 2 indicating significantly higher mineral contents except copper (Cu) in comparison to the other sites. Significant variation exists in fertilization and hatching rates during induced spawning, with the highest values recorded at site 2. It is concluded that biochemical composition of egg especially fatty acid profile and mineral content greatly influences the embryonic development and hatching success of farm reared Cirrhinus mrigala.

Understanding sex and populational differences in spatio-temporal exploration patterns and homebase dynamics of zebrafish following repeated ethanol exposure

Ethanol (EtOH) is one of the most widely consumed substance, affecting neurobehavioral functions depending on multiple environmental and biological factors. Although EtOH modulates zebrafish (Danio rerio) anxiety-like behaviors in novelty-based paradigms, the potential role of biological sex and populational variability in the exploratory dynamics in the open field test (OFT) is unknown. Here, we explored whether a repeated EtOH exposure protocol modulates the spatio-temporal exploration and homebase-related parameters in a population- and sex-dependent manner. Male and female fish from the short-fin (SF) and leopard (LEO) phenotypes were exposed to EtOH for 7 days (1 % v/v, 20 min per day). On the 8th day, the OFT was performed to assess locomotor and exploratory behaviors. We verified significant populational differences in the baseline spatio-temporal exploration patterns, supporting a pronounced anxiety in LEO with a higher homebase index compared to SF. We also found sex-dependent differences in EtOH sensitivity, where SF was more sensitive to EtOH, especially in females, which showed marked alterations in thigmotaxis and homebase occupancy. Conversely, only LEO female subjects showed increased center occupancy following EtOH. Principal component analysis (PCA) showed the main components that explained data variability, which were sex- and population-dependent. Overall, our novel findings support the utility of zebrafish-based models to assess how EtOH influences the exploratory profile in the OFT, as well as to elucidate potential differences of sex and population in the neurobehavioral responses of alcohol exposure in a translational perspective.

Parasites Infestations Status in Fish Species from River Orogodo, a Freshwater Municipal Stream, Southern Nigeria

Parasites are ubiquitous and fish are host to some of these parasites that can be zoonotic. Assessing their status and trends is vital in public health safety, and aquatic ecology. The study aimed to identify parasites, assess the prevalence, identify the infection sites and also determine the variation in infection among sexes in fish from River Orogodo, Agbor, Delta State. A total of 780 fish, comprising 23 species belonging to 12 fish families were collected between September 2014 and August 2019 using cast nets of various mesh sizes and funnel entrance traps. Fishes were identified and examined using standard morphological keys. According to established procedures, parasitological indexes were determined by inspecting various external and internal body parts. The overall prevalence recovered was 196 (25.1%) with twenty-two parasites including larvae stages both from external and internal parts of the fish. These include 5 protozoans (Microsporidium gen sp, Trichodina spp, Epistylis sp, Crytobia sp and Chilodonella sp), Myxobolus sp, 5 nematodes (Procamallanus laevionchus, Camallanus sp, Cucullanus sp, contracaecum larvae, Rhabdochona sp); 3 acanthocephalans (Acanthogyrus sp, Neoerchinorhynchus sp and Acanthocephalus sp), 4 cestodes (Monobothroides woodlandi, Wenyonia sp, Proteocephalid sp including plerocercoid larvae); 3 digeneans (Clinostomum sp, Euclinostomum heterostomum, Centrocestus sp, unidentified metacerceriae in the liver). The study revealed that female fish (32.5%) were more infected than their male counterparts (26.4%). The results indicate that fishes in River Orogodo, Delta State are hosts of various external and internal parasites, which may be of public health and aquacultural importance.

Hyperglycosylation as an Indicator of Aging in the Bone Metabolome of Oryzias latipes.

Chronological aging of bone tissues is a multi-faceted process that involves a complex interplay of cellular, biochemical, and molecular mechanisms. Metabolites play a crucial role for bone homeostasis, and a changed metabolome is indicative for bone aging, although bone metabolomics are currently understudied. The vertebral bone metabolome of the model fish Japanese medaka (Oryzias latipes) was employed to identify sex-specific markers of bone aging. 265 and 213 metabolites were differently expressed in 8-month-old vs. 3-month-old female and male fish, respectively. The untargeted metabolomics pathway enrichment analysis indicated a sex-independent increased hyperglycosylation in 8-month-old individuals. The upregulated glycosylation pathways included glycosphingolipids, glycosylphosphatidylinositol anchors, O-glycans, and N-glycans. UDP-sugars and sialic acid were found to be major drivers in regulating glycosylation pathways and metabolic flux. The data indicate a disruption of protein processing at the endoplasmic reticulum and changes in O-glycan biosynthesis. Dysregulation of glycosylation, particularly through the hexosamine biosynthetic pathway, may contribute to bone aging and age-related bone loss. The results warrant further investigation into the functional involvement of increased glycosylation in bone aging. The potential of glycan-based biomarkers as early warning systems for bone aging should be explored and would aid in an advanced understanding of the progression of bone diseases such as osteoporosis.

Structural genomic variation and behavioral interactions underpin a balanced sexual mimicry polymorphism

How phenotypic diversity originates and persists within populations are classic puzzles in evolutionary biology. While balanced polymorphisms segregate within many species, it remains rare for both the genetic basis and the selective forces to be known, leading to an incomplete understanding of many classes of traits under balancing selection. Here, we uncover the genetic architecture of a balanced sexual mimicry polymorphism and identify behavioral mechanisms that may be involved in its maintenance in the swordtail fish Xiphophorus birchmanni. We find that ∼40% of X.birchmanni males develop a "false gravid spot," a melanic pigmentation pattern that mimics the "pregnancy spot" associated with sexual maturity in female live-bearing fish. Using genome-wide association mapping, we detect a single intergenic region associated with variation in the false gravid spot phenotype, which is upstream of kitlga, a melanophore patterning gene. By performing long-read sequencing within and across populations, we identify complex structural rearrangements between alternate alleles at this locus. The false gravid spot haplotype drives increased allele-specific expression of kitlga, which provides a mechanistic explanation for the increased melanophore abundance that causes the spot. By studying social interactions in the laboratory and in nature, we find that males with the false gravid spot experience less aggression; however, they also receive increased attention from other males and are disdained by females. These behavioral interactions may contribute to the maintenance of this phenotypic polymorphism in natural populations. We speculate that structural variants affecting gene regulation may be an underappreciated driver of balanced polymorphisms across diverse species.

Effects of 17α-methyltestosterone and letrozole on growth and gonadal development in largemouth bass (Micropterus salmodies).

In order to optimize the parameters for reversing masculinization and establish the techniques for sex induction of pseudo-males and creation of all-female fry in largemouth bass (Micropterus salmodies, LMB), 15-day-old LMB (1.00 ± 0.10cm in length, 0.10 ± 0.01g in weight) were fed a diet supplemented with either 17α-methyltestosterone (MT) or letrozole (LE) and their combination. The experimental groups were M20 (20mg/kg MT), L20 (20mg/kg LE) and M10L10 (10mg/kg MT and 10mg/kg LE). The control group, named C, was not feed MT or LE. After 60 days, exogenous hormone in the diets was stopped and the effects of MT and LE on growth, male ratio, and gonadal development in LMB were evaluated. At 12-month-old, blood and gonadal tissue samples were collected to measure sex steroid hormones levels, analyze expression levels of dmrt1 and cyp19a1a genes, as well as examine the gonads morphology. The results showed no significant differences in growth between the experimental groups and the control group after a 60-day feeding period with the formulated diet (p > 0.05). The sex reversal ratio of M20, L20, M10L10 were 95.00%, 80.00%, 76.47%, respectively. The gonadal tissue sections showed that the gonadal structure of masculinized fish morphologic resembled that of control male fish. At 12-month-old, the sex reversal ratio in M20, L20, M10L10 and C groups were 100%, 86.67%, 73.33% and 50.00%, respectively. The testicular of pseudo-male fish in the M20 group exhibited well-developed morphology similarities to that of the control group males. However, the testes of pseudo-male fish in the L20 and M10L10 groups were smaller size Estradiol (E2) levels in the experimental groups was significantly lower than those in the control group females (p < 0.05), while testosterone (T) levels were significantly higher than that of the control group (p < 0.05). Compared to the female fish in the control group, pseudo-male fish from all experimental groups showed significantly upregulated expression of dmrt1 (p < 0.05), and significantly downregulated expression of cyp19a1a (p < 0.05). Pseudo-males selected from group M20 exhibited a significantly higher proportion of female offspring (92.00%) compared to the control group (46.50%). In summary, 20mg/kg MT was the optimal inducing concentration.

Molecular Cloning of the scd1 Gene and Its Expression in Response to Feeding Artificial Diets to Mandarin Fish (Siniperca chuatsi).

Background/Objectives: Stearoyl-coenzyme A desaturase 1 (SCD1) plays a crucial role in fatty acid metabolism. However, its roles in the feeding habit transformation of mandarin fish (Siniperca chuatsi) remain largely unknown. Methods: Juvenile mandarin fish (10.37 ± 0.54)g were trained to feed on an artificial diet and then divided into artificial diet feeders and nonfeeders according to their feed preference. Afterwards, the scd1 gene of mandarin fish (Sc-scd1) was identified and characterized, and its transcription difference was determined between S. chuatsi fed live artificial diets and those fed prey fish. Results: Our results show that Sc-scd1 coding sequence is 1002 bp long, encoding 333 amino acids. The assumed Sc-SCD1 protein lacks a signal peptide, and it contains 1 N-linked glycosylation site, 24 phosphorylation sites, 4 transmembrane structures, and 3 conserved histidine elements. We found that Sc-SCD1 exhibits a high similarity with its counterparts in other fish by multiple alignments and phylogenetic analysis. The expression level of Sc-scd1 was detected with different expression levels in all tested tissues between male and female individuals fed either live prey fish or artificial diets. Conclusions: In particular, the Sc-scd1 expression level was the highest in the liver of both male and female mandarin fish fed artificial diets, indicating that scd1 genes may be associated with feed adaption of mandarin fish. Taken together, our findings offer novel perspectives on the potential roles of scd1 in specific domestication, and they provide valuable genetic information on feeding habits for the domestication of mandarin fish.

Occurrence of Ectoparasites on Tilapia zillii (Red Belly Tilapia) Gervais 1848 in The Tono Reservoir, Navrongo, Ghana

This study was carried out to assess the occurrence of endoparasites in (Tilapia zillii (Gervais, 1848)) from Tono reservoir, Navrongo Ghana. A total of 120 fish samples were collected from the upstream, midstream and downstream regions of the reservoir using cast nets. All the collected fish samples were transported to the research laboratory in the University for Development Studies and examined for ectoparasites during January 2022 to August 2022. Five ectoparasites namely Trichodina sp. of Protozoans ciliates, Dactyolgyrus sp. of Monogenean, Argulus sp. and Lernaea sp. of Crustaceans and the Diplostomum sp were identified. Overall prevalence of the fish parasites was 52.32 %. Intensity of the parasites observed ranged between 1.58% to 3.52%. Highest prevalence 70 % was reported in dry season while lowest (31.67%) was reported in the rainy season. Female fish samples had higher prevalence (64.47 %) than males (27.27 %). Fishes of downstream had highest prevalence (92.5 %) than upstream (17.5 %). Fish samples with maximum length and weight were highly (65.15 %) infected than small sized fish with low body length and weight (33.33 %). It is debatable if the degree of ectoparasite activity found in this study will constitute a serious danger to the local fish population. Yet, in order to stop disease outbreaks brought on by an increase in ectoparasites, the reservoir must be given significant attention by using optimum management strategies. This study shows that dry season affects the fish business and result in poor quality fish meat with risk of diseases infection.

Parasites of African catfish (&lt;i&gt;Clarias gariepinus&lt;/i&gt;) cultured in selected homestead ponds in Rivers State, Nigeria

Fish are a major source of protein to humans and one of the constraints to improved fish production in Nigeria are parasites/parasitic diseases. A study to evaluate the parasites of African catfish (Clarias gariepinus Burchell, 1822) cultured in selected homestead ponds in Rivers State, Nigeria was conducted from January to June, 2023. One hundred and twenty catfish were randomly selected from two homestead ponds (sixty fish per pond) and categorized (sex, weight and length); each fish was analyzed for parasites (ecto and endo) using standard parasitological techniques. Descriptive analyses (mean and percentages) were used to represent data obtained and chi-square test was used to determine the level of significance with a P&lt;0.05 considered significant. An overall parasite prevalence of 30 (25.0%) was recorded in this study (P&lt;0.05) and four parasites were observed; Ichthiphitrius 14 (11.7%), Chilodinella 6 (5.0%), Trichodina 6 (5.0%) and Crytobia 4 (3.3%). Male and female fish had parasite prevalence of 8 (16.0%) and 22 (31.4%) respectively (P&gt;0.05).According to weight, parasite prevalence values of 4 (16.0%), 4 (17.4%), 8 (28.6%), 8 (30.8%) and 6 (33.3%) were recorded for 140 – 160g, 161 – 180g, 181 – 200g, 201 – 220g and 221 – 240g respectively while according to length, parasite prevalence values of 8 (21.1%), 10 (24.4%), 7 (26.9%) and 5 (33.3%) were recorded for 20 – 22cm, 23 – 25cm, 26 – 28cm and 29 – 31cm respectively (P&gt;0.05). Proper management practices should be adhered to in aquaculture to increase yield and reduce the detrimental effects of fish parasites.

Node Date Estimation of Diversified Species of Ray-Finned Fish Based on Morphological and Molecular (Vitellogenin 3) Characters Using Bayesian Analysis

Fish and other oviparous and ovoviviparous animals contain vitellogenin (Vtg), an egg yolk precursor phospholipoglycoprotein, which is the prerequisite for oocyte growth during oogenesis. Vtg is also employed as a biomarker to assess the reproductive health of female fish. In this study, we select 34 ray-finned fish under the class Actinopterygii to investigate the evolutionary time scale of their diversification age based on the molecular (vtg3 gene) as well as the combined (morphological and vtg3 gene) characters using different evolutionary models in Bayesian analysis. The analysis indicates that the species of different orders evolved in different epochs. In the case of molecular-based analysis, the orders Cyprinodontiformes and Perciformes are diversified in early Eocene to Oligocene, Anabantiformes in late Eocene, Cypriniformes in Oligocene &amp; Salmoniformes Miocene. In the case of morpho-molecular based analysis the order Cyprinodontiformes is diversified in early Eocene to Oligocene, Anabantiformes in late Eocene, Perciformes in late Eocene to Oligocene, Cypriniformes in Oligocene to Miocene &amp; Salmoniformes Oligocene to Pliocene. However, both analyses suggest that most of the selected species are diversified in Miocene, Oligocene, Eocene, and Paleocene Epoch between 5 – 65 MYA.

Evaluation of black tilapia (Oreochromis niloticus) hatchery in UPT-Perikanan Budidaya Air Tawar (PBAT) Sukorejo, Malang

Abstract Black tilapia is a freshwater fish that has become a leading commodity in the UPT-PBAT (Unit Pelayanan Teknis-Pengembangan Budidaya Air Tawar) Sukorejo Freshwater Aquaculture Fisheries with an optimal selling price. The purpose of this study was to evaluate the hatcheries activity performance in UPT-PBAT Sukorejo. The method in this research used active participation and descriptive methods. The data collection method used was from primary and secondary data. Primary data taken in this study were fertilization rate, hatching rate, and survival rate while secondary data was from literature comparison and asking directly to the staffs of UPT-PBAT Sukorejo. The results of hatchery performance showed fertilization rate of 95%, hatching rate of 98.6%, and survival rate of 93%. Hatching was carried out naturally using a 1:3 ratio (50 male fish and 150 female fish per pond). The research results indicated that hatchery activity in UPT-Freshwater Aquaculture (PBAT) Sukorejo, Malang showed good performance. However, water quality (ammonia) needs more attention to prevent negative effect in the next aquaculture cycle activity since this study found the ammonia value reached minimum tolerable value. Ammonia that exceeds the limit can cause mortality to black tilapia. Changing water is important to avoid mortality due to high ammonia content.

Exploitation and Application of a New Genetic Sex Marker Based on Intron Insertion Variation of erc2 Gene in Oplegnathus punctatus.

Spotted knifejaw (Oplegnathus punctatus), one of the most valuable mariculture species, grows with significant sexual dimorphism, with males growing significantly faster than females. O. punctatus not only has excellent growth characteristics and high food value, but also shows high economic value in aquaculture, which has become a hotspot in the field of aquaculture. The current insufficiency of sex marker identification in O. punctatus restricts the process of its unisexual breeding. Rapid identification of sex will help to study the mechanisms of sex determination and accelerate the development of sex-controlled breeding. With the completion of the sequencing of the male and female genomes of O. punctatus, the efficient and precise development of genetic sex markers has been made possible. In this study, we used genome-wide information combined with molecular biology techniques from marker sequences to further establish a rapid method for DNA insertion variant detection in the intron of O. punctatus erc2 gene, which can be used to rapidly, accurately, and efficiently identify whether DNA insertion occurs in the intron of O. punctatus erc2 gene to be detected, and to identify the sex of O. punctatus to be detected. It could also be distinguished by agarose gel electrophoresis, which would shorten the time for accurate identification and improves the detection efficiency. Homozygous comparison of male and female individuals showed that the length of the DNA fragment of the erc2 gene was 239bp on chromosome X1 and 1173bp on chromosome Y. It can therefore be inferred that a 934bp insertion fragment exists on the Y chromosome. The PCR amplification results showed that two DNA fragments of 1173bp and 239bp could be amplified in male O. punctatus, and the 1173bp fragment was a marker fragment specific to the variant intron erc2 gene, while only a single DNA fragment of 239bp was amplified in female O. punctatus. It has important significance and application value in the study of neurotransmitter transmission and environmental adaptability of female and male fish based on erc2 gene, as well as the identification of male and female sex, the preparation of high male fry, and family breeding.

Transcriptome analysis of four types of gonadal tissues in largemouth bass (Micropterus salmoides) to reveal its sex-related genes.

The sex determination system of largemouth bass (Micropterus salmoides, LMB) is XX/XY; however, the underlying molecular mechanisms involved in early sex differentiation, gonadal development, and exogenous hormone-induced sex reversal remain unknown. In this study, LMB at 15days post-hatching (dph) were fed diets containing 20mg/kg of 17α-methyltestosterone (17α-MT) or 30mg/kg of 17β-estradiol (17β-E2) for 60days, respectively. Serum steroid levels, histological observations of the gonads, and identification of sex-specific markers were employed to screen the gonads of 60-day-old normal female fish (XX-F), normal male fish (XY-M), 17β-E2 induced pseudo-female fish (XY-F), and 17α-MT-induced pseudo-male fish (XX-M) for transcriptome sequencing in order to uncover genes and pathway involved in the process of sexual reversal. The results from histology and serum sex steroid hormone analysis showed that both 17α-MT and 17β-E2 were capable of inducing sex reversal of LMB at 15dph. Transcriptome results revealed a total of 2,753 genes exhibiting differential expression, and the expression pattern of these genes in the gonads of XX-M or XY-F resembled that of normal females or males. The male sex-biased genes that are upregulated in XX-M and downregulated in XY-F are referred to as key genes for male reversal, while the female sex-biased genes that are upregulated in XY-F and downregulated in XX-M are referred to as key genes for female reversal. Finally, 12 differentially expressed genes (DEGs) related to male sex reversal were screened, including star2, cyp17a, cyp11b1, dmrt1, amh, sox9a, katnal1, spata4, spata6l, spata7, spata18 and foxl3. 2 DEGs (foxl2a and cyp19a1b) were found to be associated with female sex reversal. The changes in these genes collectively influence the direction of sex differentiation of LMB. Among them, star2, dmrt1 and cyp19a1b with significantly altered expression levels may play potentially crucial role in the process of gender reversal. The expression patterns of 21 randomly selected genes were verified using qRT-PCR which confirmed the reliability and accuracy of the RNA-seq results. These findings not only enhance our understanding of the molecular basis underlying sex reversal but also provide crucial data support for future breeding research on unisexual LMB.

Adamts9 is required for the development of primary ovarian follicles and maintenance of female sex in zebrafish.

Previous studies have suggested that adamts9 (a disintegrin and metalloprotease with thrombospondin type-1 motifs, member 9), an extracellular matrix (ECM) metalloprotease, participates in primordial germ cell (PGC) migration and is necessary for female fertility. In this study, we found that adamts9 knockout (KO) led to reduced body size, and female-to-male sex conversion in late juvenile or adult zebrafish; however, primary sex determination was not affected in early juveniles of adamts9 KO. Overfeeding and lowering the rearing density rescued growth defects in female adamts9 KO fish but did not rescue defects in ovarian development in adamts9 KO. Delayed PGC proliferation, significantly reduced number and size of Stage IB follicles (equivalent to primary follicles) in early juveniles of adamts9 KO, and arrested development at Stage IB follicles in mid- or late-juveniles of adamts9 KO are likely causes of female infertility and sex conversion. Via RNAseq, we found significant enrichment of differentially expressed genes involved in ECM organization during sexual maturation in ovaries of wildtype fish; and significant dysregulation of these genes in adamts9 KO ovaries. RNAseq analysis also showed enrichment of inflammatory transcriptomic signatures in adult ovaries of these adamts9 KO. Taken together, our results indicate that adamts9 is critical for development of primary ovarian follicles and maintenance of female sex, and loss of adamts9 leads to defects in ovarian follicle development, female infertility, and sex conversion in late juveniles and mature adults. These results show that the ECM and extracellular metalloproteases play major roles in maintaining ovarian follicle development in zebrafish.

Chromosome-level genome assemblies of vulnerable male and female elongate loach (Leptobotia elongata)

Endemic to the upper and middle reaches of the Yangtze River in China, elongate loach (Leptobotia elongata) has become a vulnerable species mainly due to overfishing and habitat destruction. Thus far, no genome data of this species are reported. As a result, lacking of such genomic information has restricted practical conservation and utilization of this economic fish. Here, we constructed chromosome-level genome assemblies for both male and female elongate loach by integration of MGI, PacBio HiFi and Hi-C sequencing technologies. Two primary genome assemblies (586-Mb and 589-Mb) were obtained for female and male fishes, respectively. Indeed, 98.22% and 98.61% of the contig sequences were anchored onto 25 chromosomes, with identification of 26.22% and 25.92% repeat contents in both assembled genomes. Meanwhile, a total of 25,215 and 25,253 protein-coding genes were annotated, of which 97.41% and 98.8% could be predicted with functions. Taken together, our genome data presented here provide a valuable genomic resource for in-depth evolutionary and functional research, as well as molecular breeding and conservation of this economic fish species.

Proteomic analysis revealed gender-related differences in the skin mucus proteome of discus fish (Symphysodon haraldi) during the parental and non-parental care periods

The discus fish, Symphysodon spp., a South American cichlid, has a unique parental care behavior where fry bite on parental skin mucus after hatching. In this study, we used LC-MS/MS technique to compare the skin mucus proteome composition of male or female discus fish during parental and non-parental care periods. By multivariate statistical analysis, we found clear separations between different periods and between different sexes of mucus proteome. Compared with non-parental female fish, parental female fish had 283 up-regulated and 235 down-regulated expressed proteins. Compared with non-parental male fish, parental male fish had 169 up-regulated and 120 down-regulated expressed proteins. The differentially expressed proteins for male fish were enriched in sulfur relay system, mucin type O-glycan biosynthesis and antigen processing and presentation pathways, while those for female fish were enriched in sulfur relay system, steroid biosynthesis and complement and coagulation cascades pathways. During the parental care, both male and female discus showed an enhanced lipid metabolism, producing more phospholipids and cholesterol. The difference is that male discus had increased tricarboxylic acid cycle producing more energy during the parental care, while females produced more nucleotides especially guanylic acid. Our study could provide new insights into the understanding of the unique mucus supply behavior of discus fish based on proteomic change.

Polystyrene nanoplastics alter intestinal toxicity of 2,4-DTBP in a sex-dependent manner in zebrafish (Danio rerio)

Nanoplastics (NPs) and 2,4-di-tert-butylphenol (2,4-DTBP) are ubiquitous emerging environmental contaminants detected in aquatic environment. While the intestinal toxicity of 2,4-DTBP alone has been studied, its combined effects with NPs remain unclear. Herein, adult zebrafish were exposed to 80 nm polystyrene nanoplastics (PS-NPs) or/ and 2,4-DTBP for 28 days. With co-exposure of PS-NPs, impact of 2,4-DTBP on feeding capacity and intestinal histopathology was enhanced in males while attenuated in females. Addition of PS-NPs significantly decreased the uptake of 2,4-DTBP in females, while the intestinal concentrations of 2,4-DTBP were not different between the sexes in co-exposure groups. Furthermore, lower intestinal pH and higher contents of digestive enzymes were detected in male fish, while bile acid was significantly increased in co-exposed females. In addition, co-exposure of PS-NPs stimulated female fish to remodel microbial composition to potentially enhance xenobiotics degradation, while negative Aeromonas aggravated inflammation in males. These results indicated that in the presence of PS-NPs, the gut microenvironment in females can facilitate the detoxification of 2,4-DTBP, while exaggerating toxiciy in males. Overall, this study demonstrates that toxicological outcomes of NPs-chemical mixtures may be modified by sex-specific physiology and microbiota composition, furthering understanding for environmental risk assessment and management of aquatic environments.