Fish Sex Research Articles

Capture of Spawning Brook Trout by Electrofishing Does Not Impair Embryo Survival

AbstractElectrofishing is widely used to capture fish in freshwater systems. Fisheries assessment and fish culture activities that occur during spawning do so in the absence of a meaningful base of evidence about the potential effects of electrofishing on fish reproduction. In this laboratory experiment, we assessed whether electrofishing adult Brook Trout Salvelinus fontinalis affected the survival of their embryos. We used two genetically distinct strains of Brook Trout (domestic and wild‐origin strains) to do so. Both strains and sexes of fish were exposed to pulsed‐DC electrofishing techniques in a fully factorial design (i.e., male shocked, female shocked, both parents shocked, or neither parent shocked [control]), after which their incubating offspring were monitored for survival to the eyed egg, alevin, and fry stages. We did not detect any effects of our electrofishing treatment or interactions with the sex or strain of the fish exposed to electrofishing, suggesting that electrofishing did not negatively impact gamete viability. Our results support the use of responsible electrofishing to collect spawning salmonids for the purpose of gamete collection for hatchery rearing.

MiRNA–mRNA Integrative Analysis Reveals the Roles of miRNAs in Hypoxia-Altered Embryonic Development- and Sex Determination-Related Genes of Medaka Fish

Recent studies have shown hypoxia to be an endocrine disruptor that impairs sex differentiation and reproductive function, leading to male-biased F1 populations in fish. However, the molecular mechanisms through which hypoxia alters fish sex differentiation and therefore sex ratios remain poorly understood. In order to understand the potential role of miRNAs in mediating hypoxia-altered sex determination and differentiation in fish, we conducted small RNA sequencing and transcriptome sequencing on marine medaka (Oryzias melastigma) embryos that were exposed to hypoxia (2.0 ± 0.2 mg O2 L–1) for 40 h (encompassing a critical window of sex determination). We identified dysregulated miRNAs and mRNAs in the hypoxia-exposed embryo, and bioinformatic analysis of the integrative small RNA sequencing and transcriptome sequencing results revealed hypoxia to cause alterations of genes related to embryonic development through miRNA regulation. Importantly, we have identified miRNA-mRNA pairs that were reported to play roles in gonad development (novel miR-145-col9a3 and novel miRNA-94- arid5b), in sex hormone response (novel miRNA-210-ca2, novel miRNA-106-nr2f2, nbr-miR-29c-nr4a1, and ola-miR-92b-akr1d1), and in sex characteristic development (novel miRNA-145-mns1, nle-miR-20-sord, and ipu-miR-219b-abcc8). Our findings highlighted the possible roles of miRNA–mRNA in regulation of embryonic development and sex determination in response to hypoxic stress.

Hematological and serum biochemical reference intervals of rainbow trout, Oncorhynchus mykiss cultured in Himalayan aquaculture: Morphology, morphometrics and quantification of peripheral blood cells

De novo reference intervals (RIs) for a total of thirty two hematological and serum biochemical attributes were established for rainbow trout (Oncorhynchus mykiss) cultured in Himalayan aquaculture system. For this purpose, long term assessment of hemato-biochemical parameters was carried over a period of one year from March 2019 to February 2020 and a total of 444 blood samples were analysed. Blood examination results were recorded systematically and reference intervals were established, notably for erythrocyte parameters: hematocrit (Hct) 29–40%, hemoglobin 8.32–12.28 g/dL, red blood cell (RBC) count 1.01–2.04 (×106/mm3); leukocyte parameters (x 103/mm3): total leukocytes 31.32–90.60, neutrophils 4.21–18.85, total lymphocytes 20.55–63.63, small lymphocytes 14.86–46.50, large lymphocytes 6.35–22.34 and monocytes 1.22–7.56; thrombocyte count 23.00–68.00 (×106/mm3). RIs were also established for red blood cell indices, vital serum constituents involved in carbohydrate, protein, lipid and nitrogen metabolism including the less known, diagnostically important, serum enzymes and electrolyte concentrations. Principal component analysis revealed that certain serum components were more efficient at distinguishing between the life stages (juvenile, adult) of fish by explaining about 92.7% of variation in the whole dataset compared to the principal hematological components which explained only about 80% of the variation. Significant (P < 0.05) differences were noted for RBC count, total leukocyte count (TLC), total protein, total cholesterol and uric acid with respect to the sex of fish. Moreover, clearly differentiable morphometric and morphological attributes were also noticed among erythrocytes, leukocytes (lymphocytes, neutrophils and monocytes) and thrombocytes. To our knowledge, the present study is the first of its kind that elucidates blood chemistry of cultured rainbow trout, O. mykiss in accordance to the guidelines framed by the American society of veterinary clinical pathologists (ASVCP). RIs reported here can help monitor the fish health status by improving the use of non-lethal diagnostics in piscine medicine.

Anticipating the Effects of Increasing Rivers’ Water Salinity for Sustainable Conservation of Tilapia Resources in Rural Coastal Zone of Benin, West Africa

The current research aimed at using the application of multi-factor models to support fisheries management decisions for successful resources’ conservation. The study was based on the tilapia species Coptodon guineensis, which is among the most widely exploited in Benin coastal zone. In an attempt to suggest conservation strategies, the phenotypic variability of 356 accessions of this species was assessed in relation with water salinity, and several interactions. The fish were collected through small-scale experimental fishing using cast nets and gillnets. The findings indicated that the salinity observed in the sampled rivers is due, at proportions ranging from 0.13% to 47%, to the sea surface salinity (SSS) of the Atlantic Ocean, suggesting a leading inland origin of the salinity of these rivers. The evidence also showed that the tilapia populations have been relatively adapted to the increasing water salinity of the sampled rivers. The fish species*river type and fish species*fish sex interactions had significant effects on phenotypic characteristics rather than river type*fish sex interaction. For an efficient conservation of these populations, two conservation areas (Lake Nokoué and Porto-Novo lagoon vs Lake Toho and Grand-Popo lagoon), could be considered for this tilapia species.&#x0D; Keywords: Aquatic salinization, population adaptation, growth parameters, interaction patterns

Influence of the seasonal and host related factors on the metazoan parasites of Chelon saliens (Mugilidae) in the Turkish coast of the Black Sea.

The leaping mullet Chelon saliens is one of the economically significant fish species and the revealing its parasite fauna in relation with some ecological and host related factors will provide new data for our current knowledge. A total of 165 leaping mullet were collected from Sinop coasts of the Black Sea in the period from September 2015 to August 2016 and investigated for parasites. Eleven parasite species including Myxobolus parvus, Myxobolus sp., Sphaerospora mugilis (Myxozoa), Ligophorus szidati, Solostamenides mugilis (Monogenea), Schikhobalotrema sparisomae, Saccocoelium tensum, Saccocoelium obesum (Digenea), Hysterothylacium aduncum (Nematoda), Neoechinorhynchus sp. (Acanthocephala) and Ergasilus lizae (Copepoda) have been identified. The overall infection prevalence, mean intensity and mean abundance values were 65.5%, 26.2 and 17.2, respectively. The overall infection prevalence was dominated by L. szidati, followed by M. parvus and Digenea-group. On the other hand, the overall mean intensity values were dominated by Digenea-group, followed by L. szidati and E. lizae, respectively, while the mean abundance values were dominated by L. szidati, followed by Digenea-group and E. lizae. The infection indices of all identified parasites were also calculated in relation with length classes and sex of fish as well as season and the differences were evaluated statistically. Seasonally significant differences in the infection prevalence and mean abundance were found for Digenea-group, Ligophorus szidati and Neoechinorhynchus sp. These differences were also significant in the length classes of Digenea-group and Ligophorus szidati. This study is the first investigation on seasonal and host related dynamics of parasites of C. saliens in the southern coasts of the Black Sea and all investigated factors were found to influence the infection indices of dominating parasite species.

Helminth endoparasites of endemic fish Pygocentrus piraya (Characiformes, Serrasalmidae) from Três Marias reservoir, Minas Gerais, Brazil.

Ten endoparasite species found in Pygocentrus piraya, which is a piranha species native to São Francisco river, were collected from 108 fish caught in Três Marias reservoir in 2004 and 2005, namely: Digenea - Austrodiplostomum sp. (metacercariae); Eucestoda - Proteocephalidae gen. sp. (plerocercoids); and Nematoda - Procamallanus (Spirocamallanus) inopinatus, Cystidicoloides fischeri and Capillostrongyloides sentinosa (adults); Spinitectus rodolphiheringi (juvenile); Hysterothylacium sp., Contracaecum sp. Type 1, Spiroxys sp. and Goezia sp. (larvae). In helminth fauna, P. (S.) inopinatus has shown higher prevalence and dominance. Fish sex has influenced the prevalence of Hysterothylacium sp., which was higher in female specimens. Longer total length of fish has positively influenced the abundance of C. sentinosa and Hysterothylacium sp.. The rainy season has favored parasitic indices, mainly P. (S.) inopinatus abundance, as well C. sentinosa and Hysterothylacium sp. prevalence and abundance. There were co-occurrences between adult and some larval nematodes. Endemic piranhas, as well as final hosts, are important intermediate and/or paratenic hosts, given the relevant number of larvae (proteocephalideans and nematodes) of heteroxene cycle found in them. Proteocephalidae gen. sp., C. sentinosa, Hysterothylacium sp., Contracaecum sp. Type 1, Goezia sp. and S. rodolphiheringi are new records parasitizing P. piraya in São Francisco basin.

Mercury in muscle and liver of Plagioscion squamosissimus (Acanthuriformes: Sciaenidae) from the Machado River, Brazilian Amazon

ABSTRACT The Machado River is the main tributary of the Madeira River in the state of Rondônia, a region that has been impacted by deforestation, livestock, urban development, alluvial gold mining and urban and industrial effluents that likely contribute to the introduction of mercury (Hg) in the aquatic system. We aimed to determine the concentrations of total Hg (THg) in muscle and liver of Plagioscion squamosissimus, a main fishing resource in the region. Fish were sampled for two years at five sites, along a 90-km stretch of the middle Machado River. THg concentrations were analyzed in 64 muscle and 54 liver samples by cold vapor atomic absorption spectrophotometry (FIMS-400). THg levels were related with fish size and sex and with periods of the hydrological cycle. THg concentrations in both organs were positively and significantly related with fish body size. There was no significant variation in THg among periods of the hydrological cycle. Mean THg concentrations in muscle (1.09 ± 0.72 mg kg-1) and liver (1.28 ± 1.23 mg kg-1) were higher than the limit established by the WHO. Our results suggest that residual mercury from former alluvial gold extraction and lixiviation of mercury naturally occurring in the soil due to large-scale deforestaion is accumulating in the aquatic food chain in the Machado River. We conclude that it is necessary to monitor the levels of mercury in commercially important fish species in the region.

Fish-for-Sex (FFS) and risk of HIV Infection among Fishers in Elmina Fishing Community in Ghana

This paper is a follow-up to a cross-sectional study which employed mix-methods for data collection and analysis to investigate a relationship between mobility and HIV risks amongst 385 fishers in Elmina. It discusses the roles of men and women in fish-for-sex (FFS), reasons for such transactional sexual activity and its implications for HIV risk infection. The theory of gender and power has been utilized to explain gender dynamics in power inequalities, and their effects on interpersonal sexual relationships between males and females within the fishing community. The paper concludes sex-division of labour exists in the study area and thrives on socio-cultural norms and power inequalities, which mainly favours men, as it gives them the power to exploit women through the supply of fish. Another observation from the paper is that as long as the female fishers require capital for their fish trade and the male fishers have greater control over the supply of the fish, the women will have very little basis to negotiate for. The paper therefore establishes linkage between fish-for-sex relationship and risk of HIV exposure among fishers in Elmina. The paper recommends empowerment of female fishers by granting them trading capital to limit their overdependence on male fishers for capital, and prevent them from exchanging sex for fish. The paper also calls for the intensification of education by relevant agencies involved in HIV education on safe sex practices through the use of condoms in fishing communities.

Roles of anti-Müllerian hormone and its duplicates in sex determination and germ cell proliferation of Nile tilapia.

Duplicates of amh are crucial for fish sex determination and differentiation. In Nile tilapia, unlike in other teleosts, amh is located on X chromosome. The Y chromosome amh (amhΔ-y) is mutated with 5 bp insertion and 233 bp deletion in the coding sequence, and tandem duplicate of amh on Y chromosome (amhy) has been identified as the sex determiner. However, the expression of amh, amhΔ-y, and amhy, their roles in germ cell proliferation and the molecular mechanism of how amhy determines sex is still unclear. In this study, expression and functions of each duplicate were analyzed. Sex reversal occurred only when amhy was mutated as revealed by single, double, and triple mutation of the 3 duplicates in XY fish. Homozygous mutation of amhy in YY fish also resulted in sex reversal. Earlier and higher expression of amhy/Amhy was observed in XY gonads compared with amh/Amh during sex determination. Amhy could inhibit the transcription of cyp19a1a through Amhr2/Smads signaling. Loss of cyp19a1a rescued the sex reversal phenotype in XY fish with amhy mutation. Interestingly, mutation of both amh and amhy in XY fish or homozygous mutation of amhy in YY fish resulted in infertile females with significantly increased germ cell proliferation. Taken together, these results indicated that up-regulation of amhy during the critical period of sex determination makes it the sex-determining gene, and it functions through repressing cyp19a1a expression via Amhr2/Smads signaling pathway. Amh retained its function in controlling germ cell proliferation as reported in other teleosts, while amhΔ-y was nonfunctionalized.

Effect of rearing system and sex on the composition and fatty acid profile of Andinoacara rivulatus meat from Ecuador

This study evaluated the influence of rearing system (cultured vs. wild rearing systems), and fish sex on carcass and flesh traits of A. rivulatus, raised in Ecuador. Three hundred mature specimens from A. rivulatus were captured, 150 from each origin. Slaughter yield and dress-out resulted similar for both rearing system, and average fillet yield for cultured fish was significantly higher than for wild fish, while cooking loss was significantly lower. Dress-out was significantly higher in females. Significant differences were found in wet percentage, ash, fat and protein content in both rearing systems, but only wet percentage was significantly affected by sex. Palmitic, oleic and arachidonic acids had the maximum percentage of saturated (SFA) and mono/poly unsaturated (MUFA/ PUFA) fatty acids, respectively. In cultured and wild fish, differentiations were also found in PUFA/SFA, docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA), atherogenicity (IA), and thrombogenicity (IT) indices, along with P, K, Mg, Cu and Fe. Sex and rearing system significantly influenced most of the analyzed characteristics of carcass and flesh of A. rivulatus. Fillet high yield and its proximate composition categorize A. rivulatus as a suitable food. These results provide valuable nutritional information about native species for consumers in Ecuador. Highlights: The rearing system (cultured vs. wild rearing systems), and fish sex affect the carcass and flesh traits of A. rivulatus. Fillet high yield and its proximate composition categorize A. rivulatus as a suitable food. The proximate composition of fillet from cultured A. rivulatus is more adequate than those of wild A. rivulatus. The cultured A. rivulatus contains higher n-3 and n-6 PUFA percentages and adequate n-3/n-6 ratio.

A Transcriptomic Analysis of Gonads from the Low-Temperature-Induced Masculinization of Takifugu rubripes.

Simple SummaryOur study analyzed the differentiation of transcriptomes in normal and sex-reverse Takifugu rubripes, and screened out 13 differentially expressed genes related to sex differentiation. This is the first report on the gonadal transcriptome of pseudo-males in Takifugu rubripes. Our results provide an important contribution to the molecular mechanism of masculinization in a cultured fish subject to low-temperature treatment.The phenotypic sex of fish is usually plastic. Low-temperature treatment induces the masculinization of Takifugu rubripes, resulting in pseudo-males (PM) with the physiological sex of a male (M) and genetic sex of a female (F). For a comparison of gonadal transcriptomes, we collected gonads from three groups of T. rubripes (F, M, and PM) for high-throughput transcriptome sequencing. The results provided 467,640,218 raw reads (70.15 Gb) and a total of 436,151,088 clean reads (65.43 Gb), with an average length of 150 bp. Only 79 differentially expressed genes (DEGs) were identified between F and PM, whereas 12,041 and 11,528 DEGs were identified between F and M, and PM and M, respectively. According to the functional annotation of DEGs, 13 DEGs related to gonadal development were screened (LOC101066759, dgat1, limk1, fbxl3, col6a3, fgfr3, dusp22b, svil, abhd17b, srgap3, tmem88b, bud4, and mustn10) which might participate in formating PM. A quantitative PCR of the DEGs confirmed the reliability of the RNA-seq. Our results provide an important contribution to the genome sequence resources for T. rubripes and insight into the molecular mechanism of masculinization in a cultured fish subject to low-temperature treatment.

Biological and Ecological Observation of Rasbora sp. for Conservation and Domestication Purpose in Lake Ie Sayang

Lake Ie Sayang provides habitat to several variety of aquatic animals including small fish such as Rasbora sp. However, their existences in nature are increasingly decline due to overfishing and degradation of its natural habitat. The objective of this study was to investigate some habitat characteristics, biological and ecological aspects of bileh fish (Rasbora sp.). Water quality parameters were recorded in situ and fish samples were collected from the water in four stations during April to July 2021. Fish sex ratio and body length-weight were measured ex situ. The data are presented in table and analyzed descriptively. The result revealed that this fish was mainly found at station 1. This station is characterized by the presence of several aquatic plants as feeding ground and fish sanctuary. This fish was easy to find in the mid-water level to water surface and near the land. The water quality parameters revealed that the temperature was in the range 30.2°C to 31.9°C, pH 6.13 to 6.35, DO 3.0 mg/l to 5.25 mg/l, and transparency 47 cm to 58 cm. Fish sex ratio showed that the overall number of females was higher than males with the average range of fish body length-weight were 34.05 mm to 41.33 mm and 1.25 g to 1.58 g respectively.

Levonorgestrel and dydrogesterone affect sex determination via different pathways in zebrafish.

Levonorgestrel (LNG) and dydrogesterone (DDG) are two commonly used synthetic progestins that have been detected in aquatic environments. They could affect fish sex differentiation, but the underlying mechanisms remain unknown. Here we investigated the effects of LNG (5 ng L-1 and 50 ng L-1), DDG (100 ng L-1) and their mixtures on gonadal differentiation and sex determination in zebrafish at transcriptomic and histological levels from 2 hours post-fertilization (eleutheroembryos) to 144 days post-fertilization (sexual maturity). Germ cell development and oogenesis pathways were significantly enriched in LNG and the mixture of LNG and DDG treatments, while insulin and apoptosis pathways in the DDG treatment. LNG and the mixture of LNG and DDG strongly decreased transcripts of germ cell development and oogenesis related genes, while DDG increased the transcripts of insulin and apoptosis related genes at 28 days post fertilization (dpf) and 35 dpf. Furthermore, DDG caused ∼ 90% males, and LNG and the mixture of LNG and DDG resulted in 100% males on all sampling dates. Specifically, most males in LNG and the mixture of LNG and DDG treatments were "Type I" males without juvenile oocytes at 28 dpf and 35 dpf, while those in DDG treatment were "Type II" and "Type III" males with a few juvenile oocytes. These results indicated that LNG and DDG promoted testicular differentiation via different pathways to cause male bias. LNG and DDG mixtures have similar effect on testicular differentiation to LNG alone. The findings from this study could have significant ecological implications to fish populations.

A meta-analytic review of fish antioxidant defense and biotransformation systems following pesticide exposure

Pesticides reach aquatic ecosystems and interact with various targets in cells of fish and other living organisms. Toxicity originates during the metabolization process, which may produce toxic metabolites or reactive oxygen species (ROS). Ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD) activities, and levels of reduced glutathione (GSH) indicate toxicants interacted with drug-metabolizing and antioxidant systems, i.e., they are biomarkers of biotransformation and oxidative stress. We meta-analytically quantified the impact of pesticides on the mean response and variability of these biomarkers. Our goals were to verify (i) the overall effect of pesticides on oxidative stress and biotransformation, and how each biomarker respond to exposure; (ii) how the life stage of fish (juvenile and adult) influence biomarkers variability and mean activity; (iii) to what extent fish sex (male, female or mixed-sex groups) modify pesticides toxicity; (iv) how different classes of pesticides, and the combination of their concentration and time of exposure, affect each biomarker. Overall, pesticides induced oxidative stress and the biotransformation system. Regardless of life stage, EROD mean activity increased significantly. In exposed juveniles, CAT and GST variability decreased and increased, respectively. CAT mean activity was higher in females, while EROD and GST activities increased in males after pesticide exposure. Organophosphorus (OPs) and organochlorine insecticides, along with imidazole and triazole fungicides, affected biomarkers the most, however the combined effect of concentration and time of exposure of OPs was not detected. Notably, imidazoles and triazoles classes increased EROD by more than 100%. Additionally, we identified research gaps, such as the lack of effect estimates of relevant pesticides on EROD (e.g., pyrethroids and neonicotinoids) and the small number of studies evaluating GSH on female fish. Future researchers may use these gaps as a guide towards enhanced experimental designs and, consequently, a better understanding of pesticide toxic effects on fish.

Accuracy of histology, endoscopy, ultrasonography, and plasma sex steroids in describing the population reproductive structure of hatchery‐origin and wild white sturgeon

Hatchery-origin white sturgeon Acipenser transmontanus in the lower Columbia River, Canada are approaching puberty, and describing the reproductive structure of the population is critical to determine if they are capable of contributing to spawning events in the wild, a key management uncertainty. Few studies have compared the accuracy of available tools (histology, ultrasound, endoscopy, and plasma sex steroids) used to assign sex and stage of maturity within the same population of prepubertal and post-pubertal sturgeon. Population reproductive structure was described using these tools in 332 hatchery-origin and 75 wild individuals over 2 years (2017 and 2018). True sex was determined using histological analysis of gonadal tissue, which is 100% accurate at assigning sex and stage of maturity in fish when germ cells are present in the biopsy. All hatchery-origin fish assessed had not reached puberty and were pre-meiotic males (n = 158) or pre-vitellogenic females (n = 174). Assignment of true sex using histology was 97% in hatchery-origin and 94% in wild fish as several biopsies did not contain germ cells. Fish with gonadal biopsies that did not contain germ cells and intersex fish (n = 3) were not included in further analyses of other tools. Accuracy in assigning sex to both the hatchery-origin (98%) and wild (100%) fish was highest using endoscopy (an otoscope). The other tools evaluated were less accurate, with 69% accuracy in hatchery-origin and 74% accuracy in wild fish for plasma sex steroids and 57% accuracy in hatchery-origin and 70% accuracy in wild fish for ultrasonography. Based on these results, endoscopy was the most reliable tool for assigning sex in both prepubertal and post-pubertal fish and can be easily complimented with histology when determining stage of maturity or describing population reproductive structure.

The Technique of Directing the Sex of Betta Fish (Betta Sp.) Larval Stage (H3, H5, and H7) using Coconut Water (Cocos Nucifera)

Betta (Betta sp.) is an anabantidae fish with sexual development that can be directed at the embryonic and larval stages. One way to direct the sex development of these fish is by using hormone therapy using natural ingredients. Coconut water is one of the natural ingredients that can be used because it contains high potassium. This potassium can convert cholesterol in fish body tissue to pregnenolone which will affect the increase in testosterone production. This study aims to determine the best dose and age group in directing the sex of Betta fish experimentally using a randomized block design (RBD) with 4 treatments and 3 replications. The immersion treatment of larvae in the age group of 3 days, 5 days, and 7 days for 15 hours with a dose of 0%, 10%, 20%, and 30% coconut water was carried out in a 3 L jar containing 30 larvae. The results showed that coconut water was able to influence the increase in the percentage of male betta fish (P &lt;0.05) with the highest value at a dose of 30% as much as 86.26 ± 8.34% and the 3 day larvae age group of 72.78 ± 16.03, and have a different effect on other treatments. In addition, the survival calculated after immersion shows a value of 100%, meaning that coconut water does not have a harmful effect on fish. Based on the results of this study, the best treatment for directing the sex of betta fish is a dose of 30% coconut water with the 3 day age group

Sex identification of morphologically‐undifferentiated Siberian sturgeon with statistical analysis of gene expression patterns

The purpose of this study was to detail a simple strategy for sexing morphologically-undifferentiated fish using statistical analysis of gene expression patterns characterized by quantitative PCR. This approach is especially relevant for species without known genomic sex markers. The method was developed for early identification of female Siberian sturgeon as part of a genomics study. That study documented activation of the enzyme 17ß-hydroxy-steroid-dehydrogenase (hsd17b1) in future ovarian tissue at 3 months of age, concurrent with a small forkhead box L2 (foxl2) peak and emerging cytochrome P450, family 19, subfamily A (cyp19a1) expression. Major cyp19a1 and foxl2 peaks occurred in presumptive female gonads at 5–6 months. This pattern suggested a genetic relay mediating estrogen production throughout differentiation, possibly to maintain gonadal femininity. Genes involved in stem cell proliferation (lim homeobox 2 (lhx2)) and somatic-germ cell interaction maintenance (iroquois homeobox 5 (irx5) and iroquois homeobox 3 (irx3)) were also expressed during molecular differentiation, at 5–6 months. The roles of lhx2, irx3, and irx5 in fish sex differentiation should be confirmed using other methodologies. These results indicate that estrogens are crucial for ovarian differentiation in basal non-teleost fish, consistent with well-established patterns in teleosts, with hsd17b1 as one of the earliest biomarkers of gonadal development.

Functioning of Mosquitofish in Different Bionomics as A Biocontrol Agent to Lower the Population of culex pipiens L. Larvae

The effect of salinity levels, water source and prey density on the predatory efficiency of mosquitofish, Gambusia affinis (Baird and Girard) against the 4th instar larvae of culex pipiens was studied. The salinity levels of 5, 10 and 15% significantly affected the rate of predation of G. affinis. All fishes have died at a salinity level of 15%. However, the predatory efficiency of both males and females was significantly higher at a 5% salinity level than that at 10%, despite fish sex or size. The number of mosquito larvae consumed by a female was higher than male at a 5% salinity level, but the reverse was observed at a salinity level of 10% despite the fish size. The type of water in which mosquito larvae or fish were bred affected the predatory efficiency of G. affinis for both male and female fishes and for all sizes of fish. Distilled water was the highest significant favorable water for predation. The density of mosquito larvae affected the predatory efficiency of G. affinis. Results showed that mosquito larvae at a density level of 40 larvae/200 ml water were the most favorable density for predation by G. affinis despite sex or size of the fish. In general, females were more efficient in predation than males despite fish size or prey density.

Keban Baraj Gölü Örencik Mevkiinden (Elazığ) Yakalanan Capoeta trutta’nın Kas Dokusundaki Bazı Ağır Metal Düzeylerinin Karşılaştırılması

Keban Dam Lake is the second largest dam lake in Turkey. In addition, it has the feature of being one of the most important dam lakes in our country in terms of both aquaculture potential and electricity generation. In this study, fish samples belong to Capoeta trutta caught from Örencik region of Keban Dam Lake were used. The concentrations of some heavy metals (copper, iron, zinc, chromium, nickel, cadmium, arsenic and mercury) in muscle of Capoeta trutta and the potential health risk from consumption of this fish species were examined. In addidion, the relationship between the heavy metal levels and some biological aspects of fish (weight, length and sex) were determined. As a result of the study, it was determined that the most and the least accumulated heavy metals in the muscle tissue of Capoeta trutta were zinc and cadmium respectively. The concentration of heavy metals showed differences according to weight, length and sex of fish. The results were found indicated that heavy metal levels in the muscle tissue of Capoeta trutta are below the tolerable values recommended by EPA, WHO and FAO. Therefore, there is not any risk for human consumption of this fish species.

Multiple sex chromosomes in teleost fishes from a cytogenetic perspective: state of the art and future challenges.

Despite decades of cytogenetic and genomic research of dynamic sex chromosome evolution in teleost fishes, multiple sex chromosomes have been largely neglected. In this review, we compiled available data on teleost multiple sex chromosomes, identified major trends in their evolution and suggest further trajectories in their investigation. In a compiled dataset of 440 verified records of fish sex chromosomes, we counted 75 multiple sex chromosome systems with 60 estimated independent origins. We showed that male-heterogametic systems created by Y-autosome fusion predominate and that multiple sex chromosomes are over-represented in the order Perciformes. We documented a striking difference in patterns of differentiation of sex chromosomes between male and female heterogamety and hypothesize that faster W sex chromosome differentiation may constrain sex chromosome turnover in female-heterogametic systems. We also found no significant association between the mechanism of multiple sex chromosome formation and percentage of uni-armed chromosomes in teleost karyotypes. Last but not least, we hypothesized that interaction between fish populations, which differ in their sex chromosomes, can drive the evolution of multiple sex chromosomes in fishes. This underlines the importance of broader inter-population sampling in studies of fish sex chromosomes.This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.