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Highly polymorphic Arctic chair (Salvelinus alpinus Linnaeus, 1758) chromosomes were studied using conventional and molecular methods. The diploid chromosome number in the studied individuals was 2n = 81 or 2n = 82, with a fundamental arm number (NF) = 100. These differences are due to Robertsonian fusions. Interindividual variation in the number and size of DAPI and [CMA.sub.3] positively stained chromatin sites was observed in studied specimens. In the case of two individuals, the subtelomeric region of the long arm (q) of the largest acrocentric chromosome (chromosome number 10) was positively stained by [CMA.sub.3] fluorochrome. Both primed in situ labelling (PRINS) and fluorescence in situ hybridization (FISH) revealed that this [CMA.sub.3]-positive region was flanked by telomeric sequences. Previously, the subterminal position of interstitial telomeric sequences located in the vicinity of the [CMA.sub.3]-positive guanine-rich chromatin have been described in two other Salvelinus species, brook trout (Salvelinus fontinalis) and lake trout (Salvelinus namaycush). Moreover, multichromosomal location and variation in size of [CMA.sub.3] bands have been observed in various Salvelinus taxa, including fishes with internally located telomeric sequences. These results suggest that relocation of [CMA.sub.3]-positive chromatin segments in these species may be facilitated by flanking interstitial telomeric sequences (ITSs). Key words: Arctic charr, chromosome rearrangements, interstitial telomeric sequences, telomeres. Les chromosomes tres polymorphes de l'omble chevalier (Salvelinus alpinus Linnaeus, 1758) ont ete etudies a l'aide de methodes conventionnelles et moleculaires. Le nombre diploide de chromosomes chez les individus etudies etait de 2n =81 ou 2n = 82 et le nombre fondamental de bras chromosomiques (NF) etait de 100. Ces differences etaient dues a des fusions robertsoniennes. De la variation entre individus a ete observee en ce qui a trait au nombre et a la taille des sites de chromatines colorees au DAPI ou au [CMA.sub.3]. Chez deux individus examines, la region subtelomerique du bras long (q) du plus grand chromosome acrocentrique (chromosome no. 10) etait marquee par le fluorochrome [CMA.sub.3]. Le marquage par synthese in situ amorcee (PRINS) et par hybridation in situ en fluorescence (FISH) ont revele que cette region marquee au [CMA.sub.3] etait bordee de sequences telomeriques. Anterieurement, la position subterminale de sequences telomeriques internes situees a proximite de chromatine riche en guanine et positive au [CMA.sub.3]avait ete decrite chez deux autres especes du genre Salvelinus, l'omble de fontaine (Salvelinus fontinalis) et l'omble du Canada (Salvelinus namaycush). De plus, de la variation quant a l'emplacement chromosomique et a la taille des bandes colorees au [CMA.sub.3] a ete observee chez plusieurs taxons de Salvelinus dont des poissons qui ont des sequences telomeriques internes. Ces resultats suggerent que la relocalisation de segments de chromatine colores au [CMA.sub.3]chez ces especes serait facilitee par la proximite de sequences telomeriques internes (ITS). Mots-cles : omble chevalier, rearrangements chromosomiques, sequences telomeriques internes, telomeres. [Traduit par la Redaction], Introduction Even though telomeric DNA sequences, consisting of [(TTAGGG/CCCTAA).sub.n] tandem repeats, are supposed to be located only at the ends of vertebrate chromosomes, in some species they are also observed [...]

A Robertsonian polymorphism resulting in diploid chromosome number ranging from 59 to 61 and constant chromosome arm number (fundamental number = 104) was observed in the albino rainbow trout (Oncorhynchus mykiss (Walbaum)) from the yellow color strain. In one individual, 90 mitotic chromosomes and 156 chromosome arms were counted, indicating the fish as a triploid. Morphology of the chromosomes, DAPI staining, and the cytogenetic location of 5S rDNA sequences showed sex-related chromosomal heteromorphism in the specimens. Additionally, length polymorphism of the X chromosome was detected in the studied individuals and two morphs of the X chromosome were described, [X.sup.L] and [X.sup.S], according to the size of its short arm (p). The [X.sup.S] was observed in the female as well as male albino rainbow trout; however, among females, no [X.sup.S][X.sup.S] genotype was found. After primed in situ labeling with 5S rDNA primers, the p-arms of both types of the X chromosome showed similar hybridization signals. On the other hand, fluorescence in situ hybridization with telomeric PNA (peptide nucleic acid) probe exhibited weak hybridization spots on the p-arm of the [X.sup.S] chromosome compared with the distinct hybridization spots observed on the [X.sup.L] p-arm. This could reflect a different telomere length on the p-arm of the [X.sup.S] and [X.sup.L] chromosomes. Partial translocation and deletion of the X chromosome p-arm are considered to be responsible for the p-arm length difference between the two morphological variants of X chromosome. Key words: albino rainbow trout, chromosomal polymorphism, sex chromosomes, triploid. Un polymorphisme chromosomique (de type Robertsonien) produisant une variation quant au nombre de chromosomes a l'etat diploide (entre 59 et 61), en depit d'un nombre constant de bras chromosomiques (nombre fundamental = 104), a ete observe chez la souche jaune de la truite arc-en-ciel (Oncorhynchus mykiss (Walbaum)). Chez un individu, 90 chromosomes mitotiques et 156 bras chromosomiques ont ete observes ce qui suggerait que cet individu etait triploide. La morphologie des chromosomes, la coloration au DAPI et la localisation des sequences d'ADNr 5S ont revele de l'heteromorphisme chromosomique lie aux chromosomes sexuels chez ces specimens. De plus, du polymorphisme pour la taille du chromosome X a ete observe et les deux formes du chromosome X ont ete nommees [X.sup.L] et [X.sup.S] en fonction de la taille du bras court (p). La forme [X.sup.S] a ete observee tant chez les femelles que les males de la truite arc-en-ciel albinos bien qu'aucune femelle [X.sup.S][X.sup.S] n'ait ete trouvee. Apres un marquage in situ realise avec des amorces specifiques de l'ADNr 5S (analyse << primed in situ labelling >>), les bras p des deux types de chromosomes X affichaient des signaux semblables. Par contre, en hybridation in situ en fluorescence avec une sonde d'acide nucleique peptidique telomerique, les signaux d'hybridation sur le bras p etaient plus faibles chez le chromosome [X.sup.S] par rapport aux signaux tres nets observes sur le bras p du chromosome [X.sup.L]. Ceci pourrait indiquer une difference dans la taille des telomeres du bras p des chromosomes [X.sup.S] et [X.sup.L]. Les auteurs discutent de la possibilite qu'une translocation et une deletion partielles des bras p du chromosome X soient a l'origine de la difference de taille des bras p chez les deux variants morphologiques du chromosome X. Mots-cles : truite arc-en-ciel albinos, polymorphisme chromosomique, chromosomes sexuels, triploide., Introduction The occurrence of atypical coloration has been found in several fish species. Among Salmonidae, individuals showing body coloration different from the wild -type coloration are observed in Salvelinus species [...]

Contents Meiotic gynogenesis was induced in the albino form of sterlet Acipenser ruthenus by activation of eggs with UV-irradiated bester ( Huso huso x Acipenser ruthenus) spermatozoa followed by inhibition of the second meiotic division performed by a heat shock. Obtained putative gynogenetic progeny were all albinos. The genetic verification based on three microsatellite DNA markers confirmed the only maternal inheritance of the progeny from the gynogenetic experimental groups. Cytogenetic analysis proved the gynogenetic sterlets were diploids. Application of the albino phenotype together with the molecular and the cytogenetic diagnostic approaches enabled to evaluate the efficiency of the spermatozoa irradiation and application of the heat shock to restore diploid state in the gynogenetic zygotes. [ABSTRACT FROM AUTHOR]

Contents Although, brook charr ( Salvelinus fontinalis Mitchill 1814) and Arctic charr ( Salvelinus alpinus Linnaeus 1758) are able to cross and give fertile offspring, their androgenetic nucleocytoplasmic hybrids are not viable. To overcome incompatibility between the egg cytoplasm of one charr species and the sperm nucleus of another charr species, application of F1 interspecific hybrids as egg donors for the purpose of androgenesis has been proposed. Here, androgenetic development of the brook charr was successfully induced in the brook charr eggs and the eggs derived from the reciprocal brook charr × Arctic charr F1 hybrids. A working androgenesis protocol included inactivation of the maternal nuclear DNA achieved by irradiation of the eggs with 420 Gy of X-rays, insemination of such treated eggs with the haploid sperm cells and exposition of the haploid androgenetic zygotes to the high hydrostatic pressure shock (51.711 MPa for 4 min) applied 420 min after insemination. Androgenetic larvae that hatched from the brook charr and the hybrid eggs were shown to be homozygous brook charr individuals. Androgenetic individuals exhibited 84 chromosomes and 100 chromosome arms ( FN), values characteristic for the brook charr diploid cells. Strategy hybridize first than induce androgenesis should be tested in order to provide androgenetic offspring in other salmonids that are able to cross and produce fertile offspring. [ABSTRACT FROM AUTHOR]

Induced development of haploid embryos (H) with only paternal (androgenesis) or maternal (gynogenesis) chromosomes requires irradiation of eggs before fertilization or activation of eggs with irradiated spermatozoa, respectively. To provide doubled haploids (DHs), androgenetic and gynogenetic haploid zygotes need to be subjected to the thermal or high hydrostatic pressure (HHP) shock to suppress the first mitotic cleavage and to double paternal or maternal haploid set of chromosomes. Androgenesis and mitotic gynogenesis (mito-gynogenesis) result in the generation of fully homozygous individuals in a single generation. DHs have been utilized in selective breeding programs, in studies concerning the phenotypic consequences of recessive alleles and to evaluate the impact of sex chromosomes on the early ontogeny. Moreover, the use of DHs for the NGS approach radically improves de novo the assembly of the genomes. However, reduced survival of the doubled haploids limits the wide application of androgenotes and gynogenotes. The high mortality of DHs may be only partly explained by the expression of recessive traits. Observed inter-clutch variation in the survival of DHs developing in eggs originating from different females make it necessary to take a closer look at the quality of the eggs used during induced androgenesis and gynogenesis. Moreover, the developmental competence of eggs that are subjected to irradiation before fertilization in order to deactivate maternal chromosomes when undergoing induced androgenesis and exposed to the physical shock after fertilization that leads to the duplication of the zygotes in both mito-gynogenesis and androgenesis may be also altered as irradiation and sublethal values of temperatures and hydrostatic pressure are considered as harmful for the cell organelles and biomolecules. Here, recently provided results concerning the morphological, biochemical, genomic, and transcriptomic characteristics of fish eggs showing high and low competence for androgenesis and mito-gynogenesis are reviewed., Competing Interests: Declarations Ethics approval Not applicable. Competing interests The author declares no competing interests., (© 2023. The Author(s).)

Expression of the telomerase reverse-transcriptase (TERT) gene and activity of telomerase have been reported in the somatic tissues and gonads in fish irrespective of their age and size. Nevertheless, little is known about TERT expression in the fish eggs. In the current study, the presence of the TERT transcripts was confirmed in the rainbow trout ovulated eggs before and after activation with nonirradiated and UV-irradiated (gynogenesis) sperm. Eggs originating from eight females had high and comparable quality expressed by similar hatching rates. However, survival of the gynogenetic larvae that hatched from eggs activated with UV-irradiated sperm and further exposed to the high hydrostatic pressure (HHP) shock for duplication of the maternal chromosomes varied between females from 2.1 ± 0.4 to 40.5 ± 2.2%. Increased level of TERT transcripts was observed in eggs originating from two females, and gametes from only one of them showed improved competence for gynogenesis (27.3 ± 1.9%). In turn, eggs from the female that exhibited the highest survival after gynogenetic activation were characterized by the lowest expression of the TERT gene. Telomerase in rainbow trout eggs may compensate erosion of the telomeres during early embryonic development; however, its upregulation does not assure better development after gynogenetic activation., Competing Interests: Declarations Ethics approval The study was carried out in strict accordance with the recommendations in the Polish Act of 15 January 2015 on the Protection of Animals Used for Scientific or Educational Purposes, Journal of Laws 2015, item 266. The protocol was approved by the Local Ethical Committee for the Experiments on Animals in Bydgoszcz (resolution no. 27/2022). Conflict of interest The authors declare no competing interests., (© 2024. The Author(s).)

Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of the Tert gene in various organs of subadult and adult diploid and triploid rainbow trout females. Upregulated Tert mRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly, Tert expression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression of Tert was observed in the liver and in the ovaries of the subadult individuals. In the triploids, Tert expression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by high Tert expression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase in Tert expression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.

The European flounder ( Platichthys flesus ), which is closely related to the recently discovered Baltic flounder ( Platichthys solemdali ), is currently the third most commercially fished species in the Baltic Sea. According to the available data from the Polish Fisheries Monitoring Center and fishermen's observations, the body condition indices of the species in the Baltic Sea have declined in recent years. The aim of the present study was to obtain information on the current patterns of genetic variability and the population structure of the European flounder and to verify whether the Baltic flounder is present in the southern Baltic Sea. Moreover, we aimed to verify whether the observed decline in the body condition indices of the species in the Baltic Sea might be associated with adaptive alterations in its gene pool due to increased fishing pressure. For this purpose, 190 fish were collected from four locations along the central coastline of Poland, i.e., Mechelinki, Władysławowo, the Vistula Lagoon in 2018, and the Słupsk Bank in 2020. The fish were morphologically analyzed and then genetically screened by the application of nineteen microsatellite DNA and two diagnostic SNP markers. The examined European flounder specimens displayed a high level of genetic diversity ( PIC = 0.832-0.903, I = 2.579-2.768). A lack of significant genetic differentiation ( Fst = 0.004, p > 0.05) was observed in all the examined fish, indicating that the European flounder in the sampled area constitutes a single genetic cluster. A significant deficiency in heterozygotes ( Fis = 0.093, p < 0.05) and overall deviations from Hardy-Weinberg expectations (H-WE) were only detected in fish sampled from the Słupsk Bank. The estimated effective population size ( Ne ) among the sampled fish groups varied from 712 (Słupsk Bank) to 10,115 (Władysławowo and Mechelinki). However, the recorded values of the Garza-Williamson indicator ( M = 0.574-0.600) and the lack of significant ( p > 0.05) differences in Heq > He under the SMM model did not support the species' population size changes in the past. The applied SNP markers did not detect the presence of the Baltic flounder among the fish sampled from the studied area. The analysis of an association between biological traits and patterns of genetic diversity did not detect any signs of directional selection or density-dependent adaptive changes in the gene pool of the examined fish that might be caused by increased fishing pressure.

Role of telomerase in specimens with retarded growth (dwarfs) has not been thoroughly examined to date. Considering that some of the fish species show correlation between somatic growth and activity of telomerase, it has been tempting to assume that pattern of telomerase activity in specimens with retarded growth and these with normal growth rate may vary. In the present research, telomerase activity has been examined in liver, skin, and muscles in the androgenetic rainbow trout ( Oncorhynchus mykiss ) with growth deficiency and their normally developed siblings. Among the examined organs, the liver showed the highest telomerase activity in all studied fish, what may be linked to the enormous regeneration capacity of the liver tissue. Although dwarf specimens examined here displayed significantly lower body size and weight they did not exhibit any significant differences in the telomerase activity measured in liver and muscle when compared to the rainbow trout without growth deficiency. In turn, telomerase activity in skin was significantly upregulated in the normally developed androgenotes. The present study indicates that dwarfism in the androgenetic rainbow trout is neither associated with ceased telomerase activity nor its decrease throughout the ontogenetic development.

Somatic growth is considered to affect pace of the telomere attrition in vertebrates. As normally developed and dwarf fish differ in the body size we have decided to compare telomere length in the rainbow trout (Oncorhynchus mykiss) with normal growth and with growth reduced due to the dwarf condition. Examined 1-year-old fish with normal and dwarf appearance were siblings originated from androgenetic fully homozygous doubled haploid (DH) line of rainbow trout. Particular dwarf individuals had body deformities such as humpback, kyphosis, and lordosis. Somatic cells of examined rainbow trout had an average telomere length between 17 and 20 kb, comparable in females and males. Dwarf rainbow trout exhibited significantly lower body length and weight than their normally developed siblings even though no differences in the telomere length were found between these fishes. Statistical analysis did not exhibit any correlation between body size and the telomere length. Equal length of telomeres observed in the studied normal and dwarf rainbow trout suggests morphological and physiological differences in fish with different growth rates do not affect dynamics of telomeric DNA. Or any variation in the telomere length might have been levelled by telomerase that in rainbow trout is active in all tissues irrespective of the individual developmental stage., (© 2021. The Author(s).)

Use of parental individuals from allochthonous lineages to produce stocking specimens resulted in genetic contamination of many local European grayling (Thymallus thymallus) populations. Stocking programs including triploid individuals that are not able to reproduce with stocks located in natural habitats due to being reproductively sterile could contribute to populations of the European grayling and prevent regional lineages from the genetic pollution. The main goal of the present research, therefore, was to provide conditions for triploidization of the European grayling and examine gonads of triploid individuals. High Hydrostatic Pressure (HHP) shock (9000 psi/5 min.) applied to activated and incubated grayling eggs at 10 °C between the 17 min. 30 sec. and 20 minute timepoints subsequent to the time of insemination resulted in inhibition of the second polar body release and triploidization. Histological analysis confirmed that all 1-yr-old cytogenetically confirmed triploids had gonadal tissues indicative of sterility with the gonads being composed of connective tissue including fibroblasts, adipocytes and degenerated epithelial structures without there being any differentiated germ cells detected. There were no differences in the body length and Fulton's condition factor between 1 year old diploid and triploid grayling, however, the average body weight was markedly less in triploid than diploid specimens. Although, 1-yr-old triploid European female and male graylings did not have fully developed gonads, before these triploid specimens are deemed safe, as a result of being reproductively sterile for stocking in natural grayling habitats, there needs to be further examination of the 2- and 3-year-old triploid specimens., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Genome sizes of eukaryotic organisms vary substantially, with whole-genome duplications (WGD) and transposable element expansion acting as main drivers for rapid genome size increase. The two North American mudminnows, Umbra limi and Umbra pygmaea, feature genomes about twice the size of their sister lineage Esocidae (e.g., pikes and pickerels). However, it is unknown whether all Umbra species share this genome expansion and which causal mechanisms drive this expansion. Using flow cytometry, we find that the genome of the European mudminnow is expanded similarly to both North American species, ranging between 4.5 and 5.4 pg per diploid nucleus. Observed blocks of interstitially located telomeric repeats in U. limi suggest frequent Robertsonian rearrangements in its history. Comparative analyses of transcriptome and genome assemblies show that the genome expansion in Umbra is driven by the expansion of DNA transposon and unclassified repeat sequences without WGD. Furthermore, we find a substantial ongoing expansion of repeat sequences in the Alaska blackfish Dallia pectoralis, the closest relative to the family Umbridae, which might mark the beginning of a similar genome expansion. Our study suggests that the genome expansion in mudminnows, driven mainly by transposon expansion, but not WGD, occurred before the separation into the American and European lineage., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) hybridize and their offspring is viable and fertile. This may be a real treat for the native European stocks of Arctic char which gene pools might be unintendedly contaminated with the genetic elements of brook trout. On the other hand, hybrids of these two species are appreciated by customers and have some potential for the aquaculture. Moreover, Salvelinus hybrids and backcross individuals are interesting models in the research focused on influence of hybridization on the genomic organization and chromosome rearrangements. Thus, the main goal of the present study was to examine chromosomes of Arctic char × brook trout F 1 , F 2 hybrids and backcross individuals and compare with genomic information concerning parental species to recognize karyotypic changes provoked by the hybridization events. Application of conventional and molecular (FISH) techniques allow to identify characteristic chromosomes for both parental species in the hybrid progeny and show multiplicity of cytotypes among different types of crosses with variability in structure and number of chromosome (81-85) and chromosome arm (99-101). Chromosome fragment was detected in the karyotype of one F 1 and one backcross individual and the presence of one triploid (3n) fish was documented. Occurrence of chromosomes containing internally located telomeric sequences (ITS) inherited after brook trout or both parental species was shown in F 1 and backcross progeny. Moreover, additional CMA 3 -positive signal on chromosome from Arctic char pair no. 2 in F 1 fish and interstitially located active NOR visible on subtelo-acrocentric (F 2 hybrid) and acrocentric (Sf × H individual) chromosomes were detected. Described polymorphic chromosomes together with specific, interstitial location of CMA 3 -positive found in F 2 and Sf × H hybrids and DAPI-positive regions observed in H × Sa fish at different uniarmed chromosomes pair presumably are remnants of chromosomal rearrangements. Provided results strongly indicate that the hybridization process influenced the genome organization in the Salvelinus hybrid progeny.

The understanding of the evolution of variable sex determination mechanisms across taxa requires comparative studies among closely related species. Following the fate of a known master sex-determining gene, we traced the evolution of sex determination in an entire teleost order (Esociformes). We discovered that the northern pike ( Esox lucius ) master sex-determining gene originated from a 65 to 90 million-year-old gene duplication event and that it remained sex linked on undifferentiated sex chromosomes for at least 56 million years in multiple species. We identified several independent species- or population-specific sex determination transitions, including a recent loss of a Y chromosome. These findings highlight the diversity of evolutionary fates of master sex-determining genes and the importance of population demographic history in sex determination studies. We hypothesize that occasional sex reversals and genetic bottlenecks provide a non-adaptive explanation for sex determination transitions., Competing Interests: QP, RF, EJ, HD, AH, BK, ER, FG, WL, LB, MT, SC, ES, GD, Fv, SC, JL, HV, KO, RG, CE, JL, CR, HH, RT, PD, KN, LJ, HP, CK, EI, VT, MS, JP, YG No competing interests declared, (© 2021, Pan et al.)

The study of fish cytogenetics has been impeded by the inability to produce G-bands that could assign chromosomes to their homologous pairs. Thus, the majority of karyotypes published have been estimated based on morphological similarities of chromosomes. The reason why chromosome G-banding does not work in fish remains elusive. However, the recent increase in the number of fish genomes assembled to the chromosome level provides a way to analyse this issue. We have developed a Python tool to visualize and quantify GC percentage (GC%) of both repeats and unique DNA along chromosomes using a non-overlapping sliding window approach. Our tool profiles GC% and simultaneously plots the proportion of repeats (rep%) in a color scale (or vice versa). Hence, it is possible to assess the contribution of repeats to the total GC%. The main differences are the GC% of repeats homogenizing the overall GC% along fish chromosomes and a greater range of GC% scattered along fish chromosomes. This may explain the inability to produce G-banding in fish. We also show an occasional banding pattern along the chromosomes in some fish that probably cannot be detected with traditional qualitative cytogenetic methods.

In the present research, the eggs from four rainbow trout females were used to provide four groups of gynogenetic doubled haploids (DHs). The quality of the eggs from different clutches was comparable, however, interclutch differences were observed in the gynogenetic variants of the experiment and the survival of DH specimens from different groups varied from 3% to 57% during embryogenesis. Transcriptome analysis of the eggs from different females exhibited inter-individual differences in the maternal genes' expression. Eggs originating from females whose gynogenetic offspring had the highest survival showed an increased expression of 46 genes when compared to the eggs from three other females. Eggs with the highest survival of gynogenetic embryos showed an up-regulation of genes that are associated with cell survival, migration and differentiation (tyrosine-protein kinase receptor TYRO3-like gene), triglyceride metabolism (carnitine O-palmitoyltransferase 1 gene), biosynthesis of polyunsaturated fat (3-oxoacyl-acyl-carrier-protein reductase gene), early embryogenic development (protein argonaute-3 gene, leucine-rich repeat-containing protein 3-like gene), 5S RNA binding (ribosome biogenesis regulatory protein homolog) as well as senescence and aging (telomerase reverse transcriptase, TERT gene), among others. Positive correlation between the genotypic efficiency and egg transcriptome profiles indicated that at least some of the differentially expressed genes should be considered as potential candidate genes for the efficiency of gynogenesis in rainbow trout.

Changes of telomere length with age were assessed in diploid and triploid rainbow trout (Oncorhynchus mykiss ) females in the cross-sectional study using Q-FISH technique. Triploid trout as sterile do not invest an energy in gametogenesis and continue to grow, whereas fertile diploid individuals suffer from declines in growth and survival during sexual maturation. However, triploid and diploid specimens exhibited similar patterns of telomere dynamics. Telomere length in the embryos, larvae and one-year-old juveniles did not change significantly. In the second year after hatching, subadults exhibited substantially shortened telomeres, while significant increase of the telomere length was reported in the three-year-old adults. On the other hand, correlation between telomere length and body size was observed in the triploid, but not in the diploid rainbow trout. Telomere shortening observed in two-year-old subadults may have been associated with the premature period of the fast growth in rainbow trout. Similar pattern of the telomere dynamics reported in the fertile diploids and sterile triploids indicated processes related to reproduction did not affect telomere dynamics in this species. Unexpected increase of the telomere length reported during the third year of life confirmed that in rainbow trout telomeric DNA shortens and lengthens, depending on the developmental stage.

Ionizing radiation is administered to damage nuclear genome in fish eggs during induced androgenesis. In this study, we examined whether 350 Gy of X-ray applied to damage chromosomes in the rainbow trout eggs affects maternal RNA. Shortly after irradiation, we did not find any symptoms of RNA degradation in the treated eggs. Significant (p < 0.01) differences between non-irradiated and irradiated eggs concerned only a few transcripts including increased expression of immediate early response 2 (IER2) and early growth response 1 (EGR1) genes observed in the irradiated eggs. Both genes belong to the group of "immediate early genes" that respond quickly to the diverse extracellular stimuli. Elevated expression of these genes was accompanied by decreased level of ssa-miR-10b-5p and ssa-miR-21b-5p (p < 0.05), for which IER2 and EGR1 are target genes. The level of RNA in the fertilized irradiated eggs was highly significantly lower than in the non-irradiated eggs (p < 0.001) and in the unfertilized irradiated eggs (p < 0.0001). However, transcriptome profiles of fertilized non-irradiated eggs and fertilized irradiated eggs did not differ significantly. Thus, we assume that reduced abundance of mRNA in the fertilized irradiated eggs was associated with post-translational degradation and clearance of the maternal transcripts rather than from the irradiation of eggs.

Ionizing radiation (IR) is applied to inactivate nuclear genome in the salmonid eggs to induce androgenetic development. However, it has been considered that doses of IR used to damage maternal chromosomes may also affect morphology of the eggs and decrease their developmental potential. Thus, the main goal of the present research was to assess alterations in the rainbow trout (Oncorhynchus mykiss) eggs caused by the high dose of IR administered during androgenesis. In the present research, rainbow trout eggs were irradiated with 350 Gy of X-rays, inseminated and exposed to the high hydrostatic pressure (HHP) shock to develop as androgenetic doubled haploids (DHs). The distribution of lipid droplets in the irradiated and non-irradiated rainbow trout eggs, survival rates and morphology of larvae from androgenetic and control groups were compared. It has been observed that non-irradiated and irradiated eggs exhibited altered distribution of lipid droplets. Most of the eggs before IR treatment displayed rather equal distribution of the oil droplets. In turn, majority of eggs studied after irradiation had coalesced lipid droplets, a pattern found in eggs with reduced quality. Incidences of abnormally developed larvae were more frequently observed among fish that hatched from the irradiated eggs. Observed changes suggest X-rays applied for the genetic inactivation of rainbow trout eggs may lead to decrease of their developmental competence., (© 2019 Blackwell Verlag GmbH.)

Poor quality eggs produced by the fully homozygous doubled haploids (DHs) may impair generation of clonal lines in fish species. In the present research, gynogenetic development of rainbow trout (Oncorhynchus mykiss) was induced in eggs originated from the DH females. Eggs were activated with the UV-irradiated grayling (Thymallus thymallus) spermatozoa and subjected to the high hydrostatic pressure (HHP) shock to provide diploid clonal individuals. Only two of four DH females produced eggs that were successfully activated by the irradiated spermatozoa and subsequently developed into the gynogenetic embryos. Survival rates of rainbow trout from the clonal lines equalled 21.5% and 19.8% during embryogenesis and decreased after hatching to 18.6% and 14.9%, respectively. Some of the dead rainbow trout clones collected between hatching and swim-up stage were emaciated and exhibited spinal deformities including scoliosis. Provided results confirmed limited developmental competences of eggs produced by rainbow trout DH females. Clonal rainbow trout developing in such eggs exhibited reduced survival and increased frequency of the body abnormalities., (© 2018 Blackwell Verlag GmbH.)

High hydrostatic pressure (HHP) causes depolymerization of the spindle microtubules. HHP applied to fish eggs prevents extrusion of the second polar body and inhibits the first cell cleavage, and it is used to produce triploids and diploid gynogenetic and androgenetic individuals. HHP has been also found to affect biomolecules including nucleic acids, and it may be presumed that HHP administered to the rainbow trout ( Oncorhynchus mykiss ) eggs disturbs cytoplasmic maternal RNA indispensable for the early embryogenesis. To verify this assumption, quality and quantity of RNA extracted from the rainbow trout eggs subjected to the high hydrostatic pressure shock were analyzed. Provided results exhibited that maternal transcriptome was resistant to a three-minute exposure to 65.5 MPa of HHP treatment. Some trend showing increase of the RNA integrity was observed in the HHP-treated eggs; however, the difference was not statistically significant. Alterations in the expression profiles in the rainbow trout eggs subjected to HHP were also negligible. Greater differences in the maternal gene expression were observed between eggs from different clutches than between HHP-treated and untreated eggs from the same clutch. It may be assumed that exposure to HHP shock was too short to modify significantly maternal transcripts in the rainbow trout eggs.

Investigation of the heterogametic sex in sterlet Acipenser ruthenus L. was performed using meiotic gynogenesis and gonadal histology. Eggs from the albino females were activated by UV irradiated sperm of wild colored males and exposed to a heat shock. The resultant fish were all albino and exhibited exclusively maternal inheritance of the microsatellite DNA markers. Cytogenetic analysis indicated that gynogenetic progeny were diploids with 120 chromosomes. Based on the histological analysis, more than 86% of the gynogenetic individuals were found to be females. Moreover, some males (7%), sterile speciemens (3.5%) and fish with unidentified gonads (3.5%) were observed among the gynogenetic fish. Presence of both females and males in the gynogenetic offspring is indicative that the heterogametic sex in sterlets is female., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Rainbow trout (Oncorhynchus mykiss Walbaum) and sea trout (Salmo trutta Linnaeus, 1758) show large karyotypic differences and their hybrid offspring is not viable due to unstable karyotype and chromosome fragmentation. However, gametes from these two species were used to induce gynogenetic development. Rainbow trout eggs activated by UV-irradiated sea trout sperm were subjected to high hydrostatic pressure (HHP) shock to prevent release of the 2nd polar body (early shock) or to inhibit the first cleavage (late shock) in order to produce diploid meiotic gynogenotes and gynogenetic doubled haploids (DHs), respectively. Cytogenetic analysis proved fish that development was induced by the sea trout spermatozoa were rainbow trout. In turn, molecular examination confirmed homozygosity of the gynogenetic DHs. Presumed appearance of the recessive alleles resulted in lower survival of the gynogenetic DH larvae (~25%) when compared to survival of the heterozygous (meiotic) gynogenotes (c. 50%). Our results proved that genomic incompatibilities between studied trout species result in the hybrid unviability. However, artificial gynogenesis including activation of rainbow trout eggs with UV-irradiated sea trout spermatozoa was successfully induced. As both species are unable to cross, application of the UV-irradiated sea trout spermatozoa to activate rainbow trout development assures only maternal inheritance with no contamination by the residues of the paternal chromosomes.

The goal of the present research was to evaluate the efficiency of 11β-hydroxyandrostenedione (OHA) applied in the diet to achieve sex reversal in the European whitefish (Coregonus lavaretus). At 32day post-hatching, fish were reared in four groups: fish fed with 10ppm of OHA (10 OHA), fish fed with 20ppm of OHA (20 OHA), fish fed without OHA (C) and fish fed without OHA and reared in the water from 20 OHA group (R). The experimental groups were conducted in separate recirculation systems and the first phase of the experiment lasted 63days. For the histological analysis of the gonads, fish from all groups were reared without OHA treatment for an additional 91days (second phase). At the end of the first phase of the experiment, survival of the whitefish ranged from 34.5±11.1% to 51.5±7.3%. The final body weight and coefficient of variation in the weight ranged from 5.6±1.2g to 6.9±1.5g and from 21.5 to 22.7%, respectively. No negative effects of OHA treatment on the growth and the survival of the whitefish were found. Six histological categories of the whitefish gonads were observed. Apart from the typical ovaries and testes, two types of the intersexual gonads (ovotestis and testis-ova) and two types of the sterile-altered gonads were distinguished. No gonadal females were found among fish from any of OHA groups. Gonadal males constituted of 60% and 50% of the fish from 10 OHA and 20 OHA groups, respectively. Intersexes were observed in all groups with the highest proportion found among fish from R variant. Rate of sterile individuals in 10 OHA and 20 OHA groups was 17% and 30%, respectively. The proportion of fish with normal testes to fish with other types of gonad varied from 0.43:1 to 1.5:1 with the higher ratio observed in both OHA groups. Lack of the females among fish from OHA groups suggested OHA affected growth and development of ovaries in the whitefish. However, a high percentage of the sterile fish in both OHA treated groups indicated application of lower doses of OHA for masculinization of the whitefish in the further research., (Copyright © 2017 Elsevier B.V. All rights reserved.)