YY Males Research Articles

Assessing the suitability of YY males and ZZ females as an invasive species population control method across life histories

Natural resource managers use tools to control invasive species. In theory, stocking YY males or ZZ females would allow managers to skew sex ratios until populations collapse. In combination with other suppression methods, such as removal, this approach could be incorporated into Integrated Pest Management plans. For example, fishery managers have stocked YY males to control isolated non-native brook trout (Salvelinus fontinalis) populations. However, life histories and demographic factors (e.g., lifespans) vary across species and could affect the feasibility of skewing sex ratios as an effective control strategy for a given population. Likewise, some species may have sex determinations that do not allow population control through sex-skewing methods. We compared five representative aquatic invasive species with global invasion ranges for potential control by skewing the sex ratio through closed population simulations: red swamp crayfish (Procambarus clarkii), zebra mussels (Dreissena polymorpha), lake trout (Salvelinus namaycush), silver carp (Hypophthalmichthys molitrix), and Nile tilapia (Oreochromis niloticus). We determined that Nile tilapia, red swamp crayfish, and zebra mussels would be the most suitable to control through skewing the sex ratio assuming appropriate sex determination exists in the species. Lake trout could be eliminated by stocking YY males but would require either long stocking periods or high stocking numbers because of the long lifespan of the species. Silver carp populations were more difficult to crash because they live longer and produce many recruits. Broadly, these patterns demonstrated that short lived species lend themselves to control by skewing the sex ratio.

Evolution of the spinach sex-linked region within a rarely recombining pericentromeric region.

Sex chromosomes have evolved independently in many different plant lineages. Here, we describe reference genomes for spinach (Spinacia oleracea) X and Y haplotypes by sequencing homozygous XX females and YY males. The long arm of the 185 Mb chromosome 4 carries a 13 Mb X-linked region (XLR) and 24.1 Mb Y-linked region (YLR), of which 10 Mb is Y-specific. We describe evidence that this reflects insertions of autosomal sequences creating a "Y duplication region" or "YDR" whose presence probably directly reduces genetic recombination in the immediately flanking regions, although both the X and Y Sex-Linked Regions are within a large pericentromeric region of chromosome 4 that recombines rarely in meiosis of both sexes. Sequence divergence estimates using synonymous sites indicate that YDR genes started diverging from their likely autosomal progenitors about 3 MYA, around the time when the flanking YLR stopped recombining with the XLR. These flanking regions have a higher density of repetitive sequences in the YY than the XX assembly and include slightly more pseudogenes compared with the XLR, and the YLR has lost about 11% of the ancestral genes, suggesting some degeneration. Insertion of a male-determining factor would have caused Y-linkage across the entire pericentromeric region, creating physically small, highly recombining, terminal pseudo-autosomal regions. These findings provide a broader understanding of the origin of sex chromosomes in spinach.

Environmental and Genetic (vgll3) Effects on the Prevalence of Male Maturation Phenotypes in Domesticated Atlantic Salmon

Pre-harvest male maturation is problematic for Atlantic salmon (Salmo salar) farmers and is regulated by the environment and genetics (e.g., vgll3). Five families of all-male salmon parr (produced using YY males crossed with XX females) with different vgll3 genotypes were split between three environmental regimes in January 2018. The “advanced maturation” regime used elevated temperature (16 °C) and continuous light from January 2018 with post-smolt maturation assessed in March 2018. The “extended freshwater” regime used ambient freshwater (1–16 °C) and simulated natural photoperiod (SNP) with post-smolt maturation assessed in November 2018. The “sea transfer” regime used ambient temperatures (1–14 °C) and SNP in freshwater until May 2018 when they were transferred to 9 °C seawater with natural photoperiod for 2.5 years (final mean weight of circa. 14 kg) and assessed for post-smolt maturation, 1 sea-winter (1 SW) maturation, and 2 sea-winter (2 SW) maturation in the autumn (November/December) of 2018, 2019, and 2020, respectively. Post-smolt maturation was highest in the advanced maturation and extended freshwater regimes (39–99% depending on family) and lowest in the sea transfer regime (0–95% depending on family). In the sea transfer regime, maturity incidence increased over time (0–95% post-smolt maturation, 1–100% 1 SW, and 50–90% 2 SW maturation, depending on family). In all regimes, those homozygous for the pre-designated vgll3 “early” maturing allele had the highest incidences of maturation whilst those homozygous for the “late” allele had the lowest. A low percentage of 2 SW phenotypic and genetic females were found (0–5% depending on family), one of which was successfully crossed with an XY male resulting in progeny with an approx. 50/50 sex ratio. These results show (i) post-smolt maturation varies dramatically depending on environment although genetic regulation by vgll3 was as expected, and (ii) crossing YY sperm with XX eggs can result in XX progeny which can themselves produce viable progeny with an equal sex ratio when crossed with an XY male.

Characterization of the sex determining region of channel catfish (Ictalurus punctatus) and development of a sex-genotyping test

Channel catfish is an important species for aquaculture that exhibits a sexually dimorphic growth in favor of males. Genetic sexing and development of sex markers are crucial for the early identification of sex and of particular genotypes (YY males) for the production of all-male population in channel catfish aquaculture. In this study, we sequenced genomic DNA from pools of males and pools of females to better characterize the sex determining region (SDR) of channel catfish and to develop sex-specific markers for genetic sexing. Performing comparative analyses on male and female pooled genomic reads, we identified a large SDR (∼8.3 Mb) in the middle of channel catfish linkage group 4 (LG04). This non-recombining SDR contains a high-density of male-specific (Y chromosome) fixed single nucleotide polymorphisms (SNPs) along with ∼ 185 kb male-specific insertions or deletions. This SDR contains 95 annotated protein-encoding genes, including the recently reported putative channel catfish master sex determining (MSD) gene, breast cancer anti-estrogen resistance protein 1 (bcar1), located at one edge of the SDR. No sex-specific SNPs and/or indels were found in the coding sequence of bcar1, but one male-specific SNP was identified in its first intron. Based on this genomic information, we developed a PCR-based sex-specific genetic test. Genotyping results confirmed strong linkage between phenotypic sexes and the identified SDR in channel catfish. Our results confirm, using a Pool-Seq approach, that channel catfish is male heterogametic (XX-XY) with a large SDR on the LG04 sex chromosome. Furthermore, our genotyping primers can be used to identify XX, XY, and YY fish that will facilitate future research on sex determination and aquaculture applications in channel catfish.

Comparing growth and body condition of wild and hatchery M YY brook trout in streams and alpine lakes

Biologists have theorized that stocking YY males (created via in-hatchery hormonal sex-reversal and selective breeding; hereafter MYY fish) could be used to eradicate unwanted non-native vertebrate populations, but little is known about the fitness of MYY individuals once released into the wild. We compared growth and body condition of stocked hatchery-reared MYY brook trout (Salvelinus fontinalis Mitchell) to wild conspecifics in two streams and two alpine lakes. Maximum age for wild fish was age 6 at one stream and age 4 or 5 at the remaining waters, whereas for hatchery MYY fish, maximum age was age 5 at one stream and age 4 at the remaining waters. Total length ranged from 103 to 359 mm for wild brook trout and 115 to 353 mm for hatchery MYY brook trout. Growth rates and body condition of stocked MYY brook trout did not differ from wild fish in the same waters. Given that the success of MYY eradication programs is primarily contingent upon MYY individuals having fitness characteristics similar to wild conspecifics, our results provide further evidence that the stocking of hatchery-reared MYY fish may be a viable tool for eradicating unwanted non-native fish populations.

Characterization of Collagen from Three Genetic Lines (Gray, Red and F1) of Oreochromis niloticus (Tilapia) Skin in Young and Old Adults.

From tilapia (Oreochromis niloticus) farming, the by-products have been identified as a source of collagen that could be used for the development of dermocosmetics or pharmaceutical products. However, the characteristics of collagen related to a specific strain or culture must be well defined prior to its application. Collagen was extracted from the skin of three strains of tilapia: red YY males (YY: two Y-type sex chromosomes), XX gray females, and the F1: offspring of crossing red YY males with XX gray females; at different ages in the adult phase, using acetic acid and pepsin enzyme. The characteristics of acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were shown by SDS-PAGE band profiles to be similar to bovine collagen type I (SIGMA), the PSC of gray tilapia being more fragile to temperature changes, consistent with the results of fractional viscosity. The characteristics of the F1 progeny were prioritized for being a commercially productive and sustainable source for the extraction of collagen, and the ASC form, being the one with the greatest stability and advantage over PSC, of importance to our investigations, leads to a controlled digestion as in the case of peptide induction, and also in the development of natural products in the pharmaceutical and/or dermocosmetic industry. Evaluations of the triple helix structure by FT-IR, X-ray diffraction and UV–visible spectroscopy give similar results between the strains: red, gray, and F1, and between ages in the adult form F1 (15, 24, and 36 months of age). Consequently, the skin of tilapia in adult form is recommended sustainably for up to 24 months of age where the collagen is obtained with the use of acetic acid without enzymatic treatment.

Sperm kinetics and motility subpopulation in XY and YY Nile tilapia (Oreochromis niloticus) males

Incorporation of YY males into the commercial farming of Nile tilapia could generate populations composed of 100% males, but first, it is necessary to evaluate the quality parameters of the spermatozoa produced by a male with two Y chromosomes. The aim of the present study was to evaluate and compare the quality, kinetics and population structure of milt samples obtained from XY and YY Nile tilapia males. We used 60 males divided by sexual genotype into two groups, XY and YY. Milt volume, sperm concentration and several parameters of motility were measured by computer-assisted sperm analysis (CASA). Motility subpopulations were identified using a principal component analysis followed by a two-step cluster procedure. The values obtained for milt volume and sperm concentration showed significant differences (p < 0.05) with YY males showing the higher values. For motility parameters, linearity and straightness index showed significantly higher (p < 0.05) values for YY males while wobble index and mean amplitude of lateral head displacement were significantly higher (p < 0.05) for XY males. Four subpopulations were identified, two for each sexual genotype. Our results suggest that sperm quality of YY males is not negatively affected by the presence of two Y chromosomes.

Production of YY males through self-fertilization of an occasional hermaphrodite in Lanzhou catfish (Silurus lanzhouensis)

Lanzhou catfish (Silurus lanzhouensis), an important commercial fish in China, takes three years to be sexually mature and males display faster growth performance than females. Thus, shortening of breeding cycle and production of all-male population in Lanzhou catfish have great significance in aquaculture. Here, we first developed an optimal method for artificial gynogenesis, through which the male heterogametic XX/XY sex determination system was revealed in Lanzhou catfish. Subsequently, sex-specific markers were identified via 2b-RAD-seq and verified in artificial breeding and wild populations. Intriguingly, a hermaphrodite Lanzhou catfish with XY genotype was occasionally obtained, whose gonad contained both mature ovarian and testicular tissues. The eggs and sperm from the intersexual gonad were used for artificial fertilization to establish a self-fertilization family, which contained 21 XX females, 25 XY males, and 12 YY males in the offspring. And the YY males are able to mate with XX females to produce all-male progenies with XY genotype. Compared with the conventional way of expending two-generation time, self-fertilization of the XY hermaphrodite saved one-generation time to produce YY males. Therefore, this study not only reveals XX/XY sex determination system in Lanzhou catfish, but also directly obtains YY males for future production of all-male population in aquaculture.

Evaluation of management factors affecting the relative success of a brook trout eradication program using YY male fish and electrofishing suppression

Removal of non-native fish populations can be crucial to the conservation of native species, but often presents a complex challenge for managers. The goal of Trojan Y chromosome (TYC) programs is to skew the non-native sex ratio until only males remain, leading to eradication. We present results from a simulation model used to explore effects of alternative management approaches on an in-progress mechanical removal and TYC program to eradicate non-native brook trout (Salvelinus fontinalis). Simulation results indicated that stocking fingerling YY males (∼137 mm) was more effective than stocking catchable-sized YY males (∼230 mm), although questions about intercohort competition warrant further investigation. Increasing the proportion of mature fingerling YY males reduced treatment time by increasing the number of YY male spawners and increasing density-dependent mortality on young, mature wild brook trout. Maximizing the spatial distribution of YY male releases may be crucial to program success but is also dependent upon immediate dispersal movements. Principles derived from our results can be broadly applied to the management of other aquatic invaded systems using TYC programs to eradicate non-native species.

Simulated Use of YY Male Stocking and Suppression for Eradicating Common Carp Populations

AbstractThe introduction and subsequent spread of Common CarpCyprinus carpiothroughout the world represent one of the most destructive and pervasive forces impacting aquatic ecosystems. Herein we use computer simulations to predict if stocking YY male carp in conjunction with manual netting or piscicide use could eradicate invasive Common Carp populations. Two forms of YY males were evaluated, including sperm‐producing (MYY) and egg‐producing (FYY) fish. A stochastic individual‐based population model was used to evaluate the effects of simulated management actions on both the abundance and extirpation probabilities of high‐ and low‐density populations. Results predicted that some YY male stocking scenarios alone could eradicate carp populations. For example, when stocking FYYcarp into low‐density populations, predicted extirpation probabilities exceeded 0.87 when stocking at least 50 carp/ha was maintained for at least 10 years. Additionally, a one‐time use of rotenone (to reduce the virtual population by 90%) plus stocking at least 50 FYYcarp/ha for at least 5 years into low‐density populations resulted in predicted extirpation probabilities exceeding 0.88. Favorable extirpation probabilities were also obtained by combining YY male stocking and either selective (i.e., no culling of stocked YY males) or non‐selective annual suppression. For example, FYYstocking with only 10% sustained, non‐selective suppression yielded extinction probabilities exceeding 95% in 15 years, while increasing suppression levels to 50% resulted in extirpation probabilities over 95% within 5 years. Without exception, MYYstocking functioned far less efficiently in simulations than FYYstocking, but MYYcarp did work in a small subset of low‐density scenarios and may also have prophylactic utility where prior eradication has occurred and where there is a high risk of re‐invasion. We conclude that stocking of YY male Common Carp is worthy of field testing, but additional simulations are needed to explore other questions not addressed in this study.

Evaluation of growth, sex (male proportion; sexual dimorphism), and color segregation in four cross combinations of different strains of XX female and YY male Nile Tilapia

AbstractFour cross combinations of different YY male and female Nile Tilapia Oreochromis niloticus strains were evaluated for growth, sex, and color segregation. Red color parental strains included blotched phenotypes. The Genetically Improved Farmed Tilapia (GIFT) was the only dark (wild‐type) color parental strain. Fish of the same age and cross were stocked in three replicate tanks for four crosses in one recirculating system for 167 days. Data recorded included feed consumed, body weight, total length, color, sex, and fillet weight. YY males crossed with GIFT females (Cross 2) exhibited superior growth that was significantly different (p &lt; .05) to other three crosses. Male proportions were 79–100%. Only YY males crossed with the LSA female strain (Cross 4) yielded 100% males, but, Cross 4's productivity was inferior to that of Cross 2. Body weight advantage of males over females was 28.7–84.2%. Color segregation indicated that red color trait in Nile Tilapia is autosomal dominant, and black patch coverage was variable. This study showed that different parental strain combinations clearly impact productivity traits, and that YY male technology combined with crossbreeding provide the opportunity for genetic improvement and development of commercially beneficial superior traits in Nile Tilapia.

DESEMPEÑO PRODUCTIVO BAJO CONDICIONES COMERCIALES DE CULTIVO DE LA PROGENIE DE MACHOS YY DE TILAPIA DEL NILO Oreochromis niloticus (L.)

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; Nile tilapia (&lt;em&gt;Oreochromis niloticus&lt;/em&gt;) is one of the most important species worldwide for aquaculture; however, the use of steroids to masculinize large volumes of fry is seen negatively by the market and environmental groups. The use of the progeny of YY males is a recent alternative that, in theory, allows to maintain the same yields, with the advantage of marketing a product free of hormones. &lt;strong&gt;Objective.&lt;/strong&gt; To evaluate the performance during growth, the gonadosomatic index, the biochemical composition, as well as the percentage of males obtained in the progeny of YY males and compare them against those obtained in a commercially masculinized progeny using flouxymesterone. &lt;strong&gt;Methodology.&lt;/strong&gt; Juveniles produced from a YY male and masculinized juveniles were stocked in external tanks of 3 m&lt;sup&gt;2&lt;/sup&gt; (in triplicate) and were cultivated for 105 days following a commercial type feeding protocol. &lt;strong&gt;Results.&lt;/strong&gt; No significant differences were detected between both progenies with respect to productive performance during growth, including fillet yield. However, the progeny of YY males showed significantly higher values (&lt;em&gt;P&lt;/em&gt; &amp;lt; 0.05) of moisture, ashes and lipids in muscle, as well as in the gonadosomatic index, probably due to the presence of a small percentage of females (8%). &lt;strong&gt;Implications.&lt;/strong&gt; The study contributes to the insertion of YY technology into the commercial culture of Nile tilapia. &lt;strong&gt;Conclusion.&lt;/strong&gt; The performance shown by the progeny of YY males compared to that of a masculinized line is similar in terms of growth, yield and survival; therefore, its implementation in the region could reduce production costs and environmental contamination, thanks to the reduction in the use of hormones.&lt;/p&gt;

Evidence of two XX/XY sex-determining loci in the Stirling stock of Nile tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) has been the subject of much research on sex determination due to the problems caused by maturation and reproduction in culture before harvest, and because of the emerging complexity of sex determination in this species. Analysis of the stock held at the University of Stirling, derived directly from Lake Manzala in Egypt about 41 years ago, detected an XX/XY locus in linkage group (LG) 1, and then a locus in LG20 that affected sex-ratio in some families, and was associated with the effects of elevated temperature on sex-ratio. Another XX/XY locus in LG23 with the candidate male-specific Amh gene was found recently to control sex determination in a Nile tilapia stock held at the Agricultural Research Organization (ARO) in Israel which was derived from a stock held at the University of Swansea, which was in turn derived from the Stirling stock. Extensive screening of the Stirling Nile tilapia stock for a marker in this male-specific Amh variant (Y-linked deletion in Amh exon VII) showed that this was present at a low frequency (7 out of 51 male broodstock, 13.73%) and associated with male phenotypic sex. It seems most likely that the dominance of the LG23 locus in sex determination in the ARO stock came about through founder effects associated with serial transfer. The presence of the previously undetected LG23 sex-determining locus may have led to some confusion in earlier attempts to develop YY males in the Stirling stock. Increased knowledge of sex determination in this species should aid marker-assisted selection (MAS) to produce all male fish to prevent unwanted reproduction in tilapia aquaculture, although the presence of multiple sex-determining loci in single stocks is likely to complicate such efforts.

Simulating effects of fitness and dispersal on the use of Trojan sex chromosomes for the management of invasive species

Abstract The use of Trojan Y chromosomes (TYC) for controlling invasive species involves manipulating the sex chromosomes of captive‐raised individuals. Following release, the offspring of these individuals consist of only one sex, thereby skewing the sex ratio of the invasive population and potentially leading to eradication. Simulation models are needed that can inform managers about how to maximize the likelihood of invasive species eradication, since implementation of this novel management approach in the field is still rare. Here, we present the first spatially explicit, mechanistic simulation model of a real‐world TYC program for invasive species eradication. Using a brook trout Salvelinus fontinalis system model, we investigated the effects of competitive and reproductive fitness of the captive‐raised YY males, dispersal behaviour upon their release and landscape heterogeneity on eradication success. Likelihood of eradication was dependent on both the competitive and reproductive fitness of the Trojan individuals. Competitive fitness (i.e. survival) had a higher threshold for eradication, below which the invasive populations were not eradicated. Movement ecology of both the wild and YY male populations was important for eradication. Under a restricted dispersal scenario for YY males following their release, the wild population was not extirpated but maintained a stable, yet reduced, population size. Analysis of landscape configuration indicated that time to eradication of local patches increased with greater connectivity within the stream network. In addition to sex ratio distortion, density‐dependent mortality resulting from outplantings made an important contribution to population decline and therefore may also affect native competitors. Synthesis and applications. The use of Trojan sex chromosomes to skew population sex ratios is a novel method for the suppression and eradication of aquatic invasive species. Results from our modelling work indicate that while eradication is possible, maximizing its likelihood requires an understanding of the fitness and movement ecology of both the wild and YY male populations of the invasive species. Both our model and the principles derived from this study related to fitness and behavioural landscape ecology can be broadly applied to other invaded species and systems.

Allelic segregation of sex‐linked microsatellite markers in Nile tilapia (Oreochromis niloticus) and validation of inheritance in YY population

Stocking of all-male fingerling produced by direct administration of male hormone 17-α-methyltestosterone is the most preferred method for present-day aquaculture of the Nile tilapia Oreochromis niloticus. However, due to the growing concern of negative impact of steroid hormone in food fish, production of ‘genetically male’ tilapia, which depends on the concrete and thorough understanding of sex determination, has long been a scientific curiosity. The objective of the present study was to identify reliable sex-linked markers and to evaluate the applicability of those markers in terms of monosex production approach. ‘XY’ neofemales were produced by using synthetic oestrogen and identified through selective breeding and progeny testing. Three females with progeny not deviating from 3:1 sex ratio (male:female) were designated as ‘XY’ neofemales and were used subsequently to produce putative YY progeny. Among the fifteen microsatellite markers tested, marker ARO172 was most informative in differentiating male and female genotypes. Twenty-seven F2 fish from three families were identified as putative YY males based on marker genotyping, and four of them were crossed to produce F3 to validate marker association by progeny testing. The YY males produced 86%–100% male progeny indicating ARO172 a unique sex-linked marker applicable in marker-assisted selection.

YY males of the dioecious plant Mercurialis annua are fully viable but produce largely infertile pollen.

Summary The suppression of recombination during sex‐chromosome evolution is thought to be favoured by linkage between the sex‐determining locus and sexually antagonistic loci, and leads to the degeneration of the chromosome restricted to the heterogametic sex. Despite substantial evidence for genetic degeneration at the sequence level, the phenotypic effects of the earliest stages of sex‐chromosome evolution are poorly known.Here, we compare the morphology, viability and fertility between XY and YY individuals produced by crossing seed‐producing males in the dioecious plant Mercurialis annua, which has young sex chromosomes with limited X−Y sequence divergence.We found no significant difference in viability or vegetative morphology between XY and YY males. However, electron microscopy revealed clear differences in pollen anatomy, and YY males were significantly poorer sires in competition with their XY counterparts. Our study suggests either that the X chromosome is required for full male fertility in M. annua, or that male fertility is sensitive to the dosage of relevant Y‐linked genes.We discuss the possibility that the maintenance of male‐fertility genes on the X chromosome might have been favoured in recent population expansions that selected for the ability of females to produce pollen in the absence of males.

SELECTION OF POTENTIAL YY MALES OF NILE TILAPIA Oreochromis niloticus (LINNAEUS, 1758) AND EVALUATION OF THE PERCENTAGE OF MALES OBTAINED

&lt;p&gt;Successful development of YY technology depends not only in the identification of YY males (YYM), but also on the evaluation of the percentage of males obtained from them. The progeny of selected potential YYM was evaluated individually in order to determine its genetic status. In total, 12 potential YYM and 12 normal females (XX) were selected. Potential YYM were selected taking into account external color, shape of the genital papillae and size. After individual crossing, a confirmed YYM was crossed consecutively with three XX females and three XY females to further assess the variation in the percentage of males obtained. A significant deviation from the 1:1 sex ratio expected for normal males (XY) was observed for ten of the twelve potential YYM that were evaluated, confirming YY status. Variation ranking between 88 to 93% in the percentage of males was observed in crosses between YYM and XX females. Finally, failure to obtain only 100% males was observed in crosses between YYM and XY females. This variation could be the result of the interaction of minor genetic parental factors or the water temperature during fry period. External parameter used for selection of potential YYM need to be optimized in further work.&lt;/p&gt;

Suitability of Microsatellite DNA Marker UNH995 in Sex Linkage Study of Nile tilapia &lt;i&gt;Oreochromis niloticus&lt;/i&gt; L

The Nile tilapia ( Oreochromis niloticus ) is one of the most commonly farmed species all over the world including Bangladesh. Monosex (male) tilapias are preferred to prevent uncontrolled reproduction by females and for the faster growth of males in case of intensive and semi-intensive aquaculture. In most of the tilapia hatchery of Bangladesh hormonal sex reversal are practiced indiscriminately by feeding androgen hormone to fry starting from their first feeding stage up to 30 days. To avoid public health concern due to direct administration of hormone in food chain, recent YY technology has become an acceptable model to produce genetically all male tilapia (GMT). However due to the plastic nature of sex determination system, the monosex production approach in Nile tilapia is yet to be practical in commercial venture. The present study was performed to analyze the suitability of sex-linked microsatellite DNA marker UNH995 for the identification of polymorphocity and informatory on allelic discrimination with polyacrylamide gel electrophoresis (PAGE) in three different families (HRT23, HRT26 and HTZF824) of Nile tilapia. Locus duplication was observed in the progeny of HRT23 and HRT26 families. In family HRT23 two alleles were equally distributed in male as well as in female offspring. Offspring of Family HRT26 contained more 231bp in female offspring, less in male offspring and totally absent in putative YY males. This information could be investigated thoroughly in future broodstock and their offspring for undertaking a monosex production approach in Nile tilapia.

A microsatellite-based linkage map of salt tolerant tilapia (Oreochromis mossambicus x Oreochromis spp.) and mapping of sex-determining loci

BackgroundTilapia is the common name for a group of cichlid fishes and is one of the most important aquacultured freshwater food fish. Mozambique tilapia and its hybrids, including red tilapia are main representatives of salt tolerant tilapias. A linkage map is an essential framework for mapping QTL for important traits, positional cloning of genes and understanding of genome evolution.ResultsWe constructed a consensus linkage map of Mozambique tilapia and red tilapia using 95 individuals from two F1 families and 401 microsatellites including 282 EST-derived markers. In addition, we conducted comparative mapping and searched for sex-determining loci on the whole genome. These 401 microsatellites were assigned to 22 linkage groups. The map spanned 1067.6 cM with an average inter-marker distance of 3.3 cM. Comparative mapping between tilapia and stickleback, medaka, pufferfish and zebrafish revealed clear homologous relationships between chromosomes from different species. We found evidence for the fusion of two sets of two independent chromosomes forming two new chromosome pairs, leading to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex determination locus in Mozambique tilapia was mapped on LG1, and verified in five families containing 549 individuals. The major XY sex determination locus in red tilapia was located on LG22, and verified in two families containing 275 individuals.ConclusionsA first-generation linkage map of salt tolerant tilapia was constructed using 401 microsatellites. Two separate fusions of two sets of two independent chromosomes may lead to a reduction of 24 chromosome pairs in their ancestor to 22 pairs in tilapias. The XY sex-determining loci from Mozambique tilapia and red tilapia were mapped on LG1 and LG22, respectively. This map provides a useful resource for QTL mapping for important traits and comparative genome studies. The DNA markers linked to the sex-determining loci could be used in the selection of YY males for breeding all-male populations of salt tolerant tilapia, as well as in studies on mechanisms of sex determination in fish.

Effects of Gender and Sex Hormones on Disease Susceptibility of Channel Catfish to Edwardsiella ictaluri

The use of monosex populations for aquaculture is becoming widely used for several species. The current studies determined if there were any differences between male and female channel catfish, Ictalurus punctatus, in disease susceptibility to Edwardsiella ictaluri, one of the most important pathogenic bacteria in catfish culture. Disease challenge experiments were carried out on fingerling channel catfish fed 17β‐estradiol or testosterone before the challenge, and on all male and on sibling all female fingerlings. All male populations were produced by mating YY males with normal XX females. Sibling females were produced by hormonally sex reversing a subpopulation of six of the all male families. Weight gain or specific growth rate did not differ in fish fed testosterone or estrogen. Fish fed the highest dose of estrogen (50 mg/kg) had a significant higher mortality (P &lt; 0.05), while mortality was similar in catfish fed 10 and 50 mg/kg of testosterone compared to controls. There were no differences in mortality between sibling males and females. These data indicate no increased disease susceptibility to E. ictaluri between males and females or due to exogenous sex hormones. Production of all male catfish for culture can proceed without concern for disease susceptibility to E. ictaluri.