Cell lines were established from spleen and heart tissues of a juvenile white sturgeon Acipenser transmontanus and designated WSS-2 and WSH-1, respectively. Isoenzyme analyses of both lines confirmed their host of origin. Both lines were hypotetraploid and possessed micro- and macrochromosomes. The modal chromosome number for the WSS-2 line was 219; the WSH-1 line had a bimodal distribution with modes of 237 and 243. The effects of temperature on growth and susceptibility to selected viral pathogens were examined for the WSS-2 line. Cell replication occurred at 15–30°C, optimum temperature was 25°C. Cell survival was observed after 11 d at 10°C but not at 35°C. The WSS-2line was refractory to infections with channel catfish virus (CCV) and infectious pancreatic necrosis virus (IPNV) but susceptible to infectious hematopoietic necrosis virus (IHNV) and white sturgeon iridovirus (WSIV). The need for cell lines from the host of origin in studies of viral pathogens of fish was demonstrated by the ability of the WSS-2 line to support replication of WSIV.

The taxonomic relations between the Sakhalin and North American green sturgeons were revaluated based on afresh conducted comparative morphological analysis of both sturgeons, as well as a renovation of literature cytogenetic, molecular and morphological data. The comparative analysis of different data sets demonstrates the validity of the Sakhalin sturgeon A. mikadoi which differs from the North American green sturgeon A. medirostris in the karyotype structure, the nuclear DNA content value, and several morphological characters. The key for their identification is presented.

Serebryakova EV. Arefjev VA. Vasiliev VP. Sokolov LI

The analysis is made on the karyotype of giant sturgeon based on the spiralization index aimed at precise identiftcation of certain pairs of homologous chromosome by using the polykaryogram method. The comparison of karyological data on protein genetics and results of hybridological analysis has indicated the affinity of giant sturgeon with ship sturgeon and sterlet as well as differences between giant sturgeon on the one hand and Russian and Siberian sturgeons on the other hand. Some changes are suggested to be introduced into the systematics of sturgeon.

The comparative morphological study in different Acipenseriform species demonstrates that there are only two morphological features combining the kaluga and the great sturgeon and separating them from other sturgeons, namely the shape of a mouth and the manner attaching of gill membranes to isthmus in adult specimens; whereas many morphological characters are different in these species. The relations of morphological similarity/distinction among different sturgeon species and polyphyletic origin of genus Huso revealed by both molecular and cytogenetic studies presume the restoration of initial taxonomic states for the great sturgeon and kaluga as members of the same genus Acipenser, namely A. huso and A. dauricus.

Hardie DC. Hebert PDN.

Cytological and organismal characteristics associated with cellular DNA content underpin most adaptionist interpretations of genome size variation. Since fishes are the only group of vertebrate for which relationships between genome size and key cellular parameters are uncertain, the cytological correlates of genome size were examined in this group. The cell and nuclear areas of erythrocytes showed a highly significant positive correlation with each other and with genome size across 22 cartilaginous and 201 ray-finned fishes. Regressions remained significant at all taxonomic levels, as well as among different fish lineages. However, the results revealed that cartilaginous fishes possess higher cytogenomic ratios than ray-finned fishes, as do cold-water fishes relative to their warm-water counterparts. Increases in genome size owing to ploidy shifts were found to influence cell and nucleus size in an immediate and causative manner, an effect that persists in ancient polyploid lineages. These correlations with cytological parameters known to have important influences on organismal phenotypes support an adaptive interpretation for genome size variation in fishes.

Des caractéristiques cytologiques et de l’organisme entier, lesquelles sont associées avec le contenu en ADN, sous-tendent la plupart des interprétations adaptivistes de la variation quant à la taille des génomes. Puisque les poissons constituent le seul groupe de vertébrés chez lequel les relations entre la taille du génome et certains paramètres cellulaires clés sont incertains, les corrélations entre les caractéristiques cytologiques et la taille du génome ont été examinées chez ce groupe d’espèces. Il existait une corrélation positive très significative entre les volumes de la cellule et du noyau chez les érythrocytes ainsi qu’entre ceux-ci et la taille du génome chez 22 espèces de poissons cartilagineux et chez 201 espèces de poissons à nageoires rayonnées. Les régressions sont demeurées significatives à tous les niveaux taxonomiques ainsi que chez tous grands groupes de poissons. Les résultats ont cependant révélé que les poissons cartilagineux possédaient des ratios cytogénomiques plus élevés que les poissons à nageoires rayonnées, tout comme le font les poissons d’eau froide par rapport aux poissons d’eau chaude. Des accroissements de la taille des génomes dus à des changements de ploïdie influençaient directement et immédiatement la taille de la cellule et du noyau, un effet qui persiste chez les anciennes lignées évolutives polyploïdes. Ces corrélations avec des paramètres cytologiques connus pour exercer des influences importantes sur le phénotype de l’organisme viennent appuyer une interpretation adaptative de la variation de la taille du génome chez les poissons.

Vasiliev VP. Sokolov

The method described makes use of cells from the lymphoid organ, which has a high degree of mitotic activity. The diploid number of the Siberian sturgeon, Acipenser baeri, was found to be 249 plus or minus 5, and the number of chromosome arms 308 plus or minus 8.

Song, S. Liu H. Sun D. Fan Z.

Metaphase chromosome specimens of Amur Sturgeon, injected with fetal calf serum, were prepared from short-term culture of kidney cells with air-drying technique. Its diploid chromosome number is 2n=238±8. Karyotype consists of 78m+l2sm+28st, t + 120±mc, NF: 328±. Diploid nucleus DNA content was measured from the peripheral erythrocytes, using flow cytometer (FACStar Pus, made in USA) and erythrocytes of chick (Gallus sp) as internal standard. DNA content of the ash is 11.73 ± 0.68 pg/N and the ratio to that of chickens is 5.06

Song, S. Liu H. Sun D. Fan Z.

Metaphase chromosome specimens of Amur Sturgeon, injected with fetal calf serum, were prepared from short-term culture of kidney cells with air-drying technique. Its diploid chromosome number is 2n=238±8. Karyotype consists of 78m+l2sm+28st, t + 120±mc, NF: 328±. Diploid nucleus DNA content was measured from the peripheral erythrocytes, using flow cytometer (FACStar Pus, made in USA) and erythrocytes of chick (Gallus sp) as internal standard. DNA content of the ash is 11.73 ± 0.68 pg/N and the ratio to that of chickens is 5.06

1) The variability of fishes is an adaptive property. The range of variability is broader in eurybiotic fishes than in steno- biotic ones. Variability in fish species is lower in stenobiotic fishes inhabiting the waterbodies in lower latitudes. 2) Eurybiotic fishes and especially euryphagous ones, occupy broader ecologi- cal niches and a wider range of habitats. At the same time the effectiveness of energy utilisation in eurybiotic fish is lower than in stenobiotic fishes. 3) The range of variability of characters and properties in marine fishes of the same geographical zone is in general lower than in equivalent freshwater fishes. 4) The variability of characters in fishes is correlated with chromosome number, DNA content, and GC value. 5) The range of variability of characters in fishes, the chromosome number, and the DNA content decreases while the effectiveness of food conversion increases from higher to lower latitudes. 6) The phylogenetic status of teleost fishes in general is connected with a diminishing range of variability, with a de- crease in chromosome number and DNA content. The effectiveness of utilisation of energetic resources increases from lower groups of teleost fishes to higher ones.

The hypothesis on tetraploid origin of North American paddlefish, Polyodon spathula based on simple karyotyping of 31 cells from 2 males by Dingerkus & Howell (1976) was recently confirmed by molecular phylogeny but chromosomes of this highly endangered, ancient fish has never been analysed using both conventional and molecular cytogenetic protocols. We examined chromosomes of paddlefish derived from leukocyte cultures using sequentially Giemsa- and Ag-staining, CMA3- and DAPI-fluorescence and FISH with 28 S, 5 S rDNA and telomeric (TTAGGG)n probes. Diploid chromosome number 2n=120 (48 macro-, 72 microchromosomes) and macrochromosomes apparently grouped in quadruplets, including acrocentric “acipenseriform” chromosome marker, were reconfirmed. The major (28S) and minor (5S) rDNA sites co–localize in p arms of four (likely) smallest metacentric chromosomes; while all four 28 S sites displayed signal with the same intensity, 5S sites displayed one pair with remarkable stronger signal intensity. Telomeric signals were situated in telomeres, no interstitial telomeric site was observed. CMA3-fluorescence revealed only four signals onto p arms of four (likely) smallest metacentric chromosomes corresponding to rDNA sites and Ag-staining and four signals in pericentromeric regions of acrocentric “acipenseriform” marker. The DAPI-fluorescence revealed only weak signals in centromeric regions of four the second largest and four smaller metacentric chromosomes and also in pericentromeric region of a one submetacentric pair of chromosomes (i.e., not in quadruplet) in karyotype. Such evident fourfold chromosomal characteristics support the hypothesis about tetraploid origin of paddlefish but presence of a single submetacentric pair with AT-rich heterochromatin indicates some remodelling of its karyotype after tetraploidization.

Van Eenennaam AL. Murray JD. Medrano JF

The surface-spreading synaptonemal complex (SC) technique was used to visualize the process of chromosome synapsis in white sturgeon spermatocytes. Pachytene nuclei had various numbers of univalents (0.3) and self-paired foldback elements with no obvious centromeric region (1.7) that may represent accessory chromosomes. The total SC length was 482 (+/- 56) um and the average number of SC elements per nucleus was 139 (+/- 3.4). This SC number suggests a higher chromosome number than had been reported in previous mitotic studies (2n = 248 +/- 8). There was variation in the SC count both within and between animals. A representative SC karyotype is presented and some differences between the mitotic and meiotic karyotypes for this species are discussed. There was no evidence of multivalent formation, suggesting that the process of diploidization has gone to completion in the males of this ancient polyploid species. Each SC had lateral elements of equal length, and no bivalent exhibited the atypical pairing behavior that is often characteristically associated with heteromorphic sex chromosomes, suggesting that the male is not the heterogametic sex in white sturgeon. Key words: fish, karyotype, meiosis, synaptonemal complex, white sturgeon.

Résumé : La technique d.étalement en surface des complexes synaptonémaux (SC) a été employée pour examiner le processus de synapsis chez les spermatocytes de l.esturgeon blanc. Des noyaux en pachytène montraient un nombre variable d.univalents (0.3) et des éléments repliés sur eux-mêmes sans centromère apparent (1.7) qui représentent potentiellement des chromosomes accessoires. La longueur totale de complexe synaptonémal était de 482 (+/- 56) um et le nombre moyen d.éléments SC par noyau était de 139 (+/- 3,4). Ce nombre de SC suggère la présence d.un nombre de chromosomes plus élevé que ce qui avait été rapporté dans les études mitotiques antérieures (2n = 248+/- 8). Il existait une variation quant au nombre de SC entre individus ainsi qu.à l.intérieur de ceux-ci. Un caryotype représentatif du complexe synaptonémal est présenté et certaines différences entre les caryotypes mitotique et méiotique pour cette espèce sont discutées. Aucune indication de la formation de multivalents n.a été observée ce qui suggère que le processus de diploïdisation est complété chez les mâles de cette espèce polyploïde ancienne. Chaque SC possédait des éléments latéraux de longueur égale et aucun bivalent ne montrait un appariement atypique qui est souvent associé avec la présence de chromosomes sexuels hétéromorphes. Ceci suggère que le mâle n.est pas le sexe hétérogamétique chez l.esturgeon blanc. Mots clés : poisson, caryotype, méiose, complexe synaptonémal, esturgeon blanc.

Sturgeons, shovelnoses and paddlefishes (Acipenseriformes with families Polyodontidae and Acipenseridae) include three evolutionary (paleo) ploidy levels: tetraploid (4n, ~120 chromosomes), octaploid (8n, ~240 chromosomes) and also dodecaploid (12n, ~360 chromosomes in A. brevirostrum). While paleotetraploid level is present in Polyodontidae, the elevated ploidy levels are confined to several species of sturgeons of the genus Acipenser. Sturgeons are also notoriously known to hybridise irrespective to ploidy level producing progeny of intermediate ploidy levels. Larger screening of ploidy level in several European hatcheries revealed a number of such ploidy intermediates indicating uninformed hatchery practices in artificial reproduction of sturgeons. To unravel hybrid and ploidy diversity of sturgeons, we systematically mated pure 4n (A. ruthenus) and 8n (A. gueldenstaedtii, A. baerii) individuals as controls with males and/or females of 6n (~180 chromosomes), 10n (~300 chromosomes) and 12n ploidy levels that were identified in breeding stocks of A. ruthenus, A. gueldenstaedtii and A. baerii. The respective progenies were reared up to check ploidy level using flow cytometry, image cytometry of erythrocyte nuclear dimensions and direct karyotyping. Each crossing between different ploidy level individuals unambiguously confirmed intermediate ploidy levels in progenies resulting in production of 5n (~150 chromosomes), 6n (~180chromosomes), 7n (~210 chromosomes), 9n (~270 chromosomes) and 10n (~300 chromosomes). A part of such progenies is reared up to verify expected fertility. The evident ploidy plasticity of sturgeons with apparent multiples of about 30 chromosomes might suggest that these semi-haploid units (n = 60, n/2 = 30) still reflect original haploid genome of extinct sturgeon paleodiploid ancestor and reinforce the hypothesis of Vasil´ev regarding hybrid origin of sturgeons through the reticulate speciation.

Sturgeons (Chondrostei: Acipenseriformes) display markedly disjunction distributions with a wide distribution in the northern hemisphere. Their unique benthic specializations and conserved morphology, evolutionary age, the variation in their basic diadromous life history, and the large public interest due to their near extinction or critically endangered status make sturgeons and paddlefishes interesting groups for molecular and cytogenetic studies. From altogether 27 acipenseriform species, seventeen species are supposed to be critically endangered, two species are classified as endangered, four species are vulnerable and other species are near threatened or in low-risk (IUCN Red list 2010). Sturgeons are characteristic by a relatively high number of chromosomes in cell nuclei and differences in ploidy levels. Sturgeons displayed a strong tendency for interspecific and inter-generic hybridization under altered environmental conditions as well as under conditions of artificial propagation. Almost 20 inter-specific sturgeon hybrids were described. The decrease of natural populations and tendencies leading to restocking may result in uncontrolled restocking, production of hybrid specimens (even with non-native species) and decrease of natural genetic diversity of species in their original distribution area. Identification of parental species of natural hybrids by modern methods of molecular biology is still not easy. Here, we attempt to briefly summarize the major aspects of sturgeon genetics and cytogenetics related to ploidy levels and interspecific hybridization.