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PubMedDate not supplied

Biplexiform ganglion cells, characterized by dendrites in both outer and inner plexiform layers, are regular, mosaic-forming elements of teleost fish retinae.

Biplexiform ganglion cells were labelled by retrograde transport of HRP in five species of marine fish from the neoteleost acanthopterygian orders Perciformes and Scorpaeniformes. Their forms and spatial distributions were studied in retinal flatmounts and thick sections. Biplexiform ganglion cells possessed sparsely branched, often varicose, dendrites that ramified through the inner nuclear layer (INL) to reach the outer plexiform layer (OPL), as well as conventional arborizations in the most sclerad part of the inner plexiform layer (IPL). Their somata were of above-average size and were displaced into the vitread border of the INL. Mean soma areas ranged from 99 +/- 6 microns2 in Bathymaster derjugini (Perciformes) to 241 +/- 12 microns2 in Hexagrammos stelleri (Scorpaeniformes), but were similar in each species to those of the outer-stratified alpha-like ganglion cells, whose dendritic trees occupied the same IPL sublamina. In the best-labelled specimens, biplexiform cells formed clear mosaics with spacings and degrees of regularity much like those of other large ganglion cells, but spatially independent of them. Biplexiform mosaics were plotted in three species, and analyzed by nearest-neighbor distance and spatial correlogram methods. The exclusion radius, an estimate of minimum mosaic spacing, ranged from 113 microns in Hexagrammos stelleri, through 150 microns in Ernogrammus hexagrammus (Perciformes), to 240 microns in Myoxocephalus stelleri (Scorpaeniformes). A spatial cross-correlogram analysis of the distributions of biplexiform and outer-stratified alpha-like cells in Hexagrammos demonstrated the spatial independence of their mosaics. Similar cells were previously observed not only in the freshwater cichlid Oreochromis spilurus (Perciformes) but also in the goldfish Carassius auratus (Cypriniformes) which, being an ostariophysan teleost, is only distantly related. Thus, biplexiform ganglion cells may be regular elements of all teleost fish retinae. Their functional role remains unknown.

Animals↗
PubMed2002

Evidence for a slowed rate of molecular evolution in the order acipenseriformes.

A test of the hypothesis that the members of the order Acipenseriformes (sturgeons and paddlefishes) possess a slowed rate of molecular evolution was carried out by conducting relative-rate comparisons with representatives of four groups of teleost fishes (Cypriniformes, Elopomorpha, Salmonidae, and Percomorpha) using 21 nuclear or mitochondrial protein loci and the nuclear and mitochondrial small subunit rRNA genes, obtained from the literature or our own research. In 70 out of 81 comparisons between individual taxa (86%), acipenseriform sequences showed slower rates of change than the homologous teleost loci examined. When teleost sequences are considered together, 21 of the 23 loci show slower rates of substitution in the acipenseriform lineage. Teleost proteins show 1.85 times as many unique amino acid differences as acipenseriform proteins, when both are compared with outlier sequences. These results support a hypothesis of slowed molecular evolutionary rate in the Acipenseriformes.

Animals↗
PubMed1993

Muscarinic cholinoceptors that mediate pigment aggregation are present in the melanophores of cyprinids (Zacco spp.).

Like melanophores of many teleosts, those of the dark chub, Zacco temmincki, and the common minnow, Z. platypus (Cyprinidae, Cypriniformes) responded to norepinephrine (NE) by the aggregation of pigment. It was further found that some melanophores were responsive to acetylcholine (ACh) in the same way. The response to NE was blocked by an alpha-adrenergic blocker, phentolamine, whereas the response to ACh was not. By contrast, two muscarinic cholinoceptor antagonists, namely, atropine and scopolamine, effectively blocked the action of ACh. The pigment aggregation due to the liberated sympathetic neurotransmitter was blocked by phentolamine but not by cholinergic blockers. These results suggest that, although the melanophores of these species are controlled in an orthodox manner by the sympathetic nervous system, some of them possess extra muscarinic cholinoceptors that also mediate the aggregation of pigment. The present report is the first to describe the presence of cholinoceptors on the chromatophores in species of fish other than those that belong to the order Siluriformes. The evolutionary implications of these findings are discussed.

Acetylcholine↗
PubMed1998

Comparison of fast startle responses between two elongate bony fish with an anguilliform type of locomotion and the implications for the underlying neuronal basis of escape behavior.

A comparative anatomical and behavioral approach was used to elucidate the role of medullary networks associated with Mauthner cells (M-cells) in determining the type of fast startle responses of elongate bony fish with an anguilliform type of locomotion. The M-cell initiates fast startle responses in goldfish and is thought to initiate such responses in other fish as well [Wilson, 1959; Eaton et al., 1977; Currie and Carlsen, 1987; Currie, 1991]. Goldfish M-cells have a specialized structure, termed an axon cap, that surrounds their axon hillock-initial segment region and is critical for the control of M-cell excitability. The M-cell axon cap is present in some elongate fish such as the African lungfish (Protopterus, Lepidosireniformes) and absent in others such as the American eel (Anguilla, Anguilliformes). The lungfish startle response is characterized by a rotation of the head and upper trunk, similar to the initial phase of the goldfish (Carassius, Cypriniformes) startle response. The American eel, on the other hand, displays a withdrawal-type startle response. We hypothesize that the withdrawal-type startle response of the American eel results from the absence of inhibitory networks associated with the M-cell axon cap. The correlation of the absence of an axon cap and a withdrawal-type startle response may be a general feature of all Anguilliformes and elongate ray-finned fish with an anguilliform type of locomotion.

Anguilla↗
PubMed2000

Fiber connections of the corpus mamillare in a percomorph teleost, tilapia Oreochromis niloticus.

The hypothalamus and perhaps its function appear to be similar among vertebrates. Thus, studying the teleostean hypothalamus could be a good model for understanding common neural circuits and mechanisms retained through the vertebrates. However, connections of the inferior lobe, which is considered the hypothalamus in teleosts, is poorly known. The corpus mamillare (CM) is a nucleus of the inferior lobe named after the mammalian mamillary body based on similarities in external morphology. Afferent connections of the CM have been reported only in cypriniform teleosts. These include projections from the nucleus pretectalis superficialis pars magnocellularis, a nucleus lacking in percomorph teleosts, and projections from the secondary gustatory nucleus. Efferent connections of the CM have not been reported in teleosts. In the present study, the CM and its subdivisions and the connections of these subnuclei were identified in isolated and maintained brains of tilapia Oreochromis niloticus by local DiI and biocytin injection. Afferent connections confirmed by reciprocal injections were from the nucleus diffusus lobi inferioris (NDLI) and the nucleus diffusus tori lateralis (NDTL). Efferent connections of each CM subnuclei were also reciprocally confirmed. These connections were to the area dorsalis pars medialis of the telencephalon, the nucleus ventromedialis (NVM) of the thalamus, the tectum opticum (TO), and the nucleus posterioris periventricularis. Because the NDLI is known to receive gustatory information in tilapia, the CM could relay gustatory inputs to multisensory areas, the TO and NVM, for which there are no current reports regarding gustatory inputs.

Afferent Pathways↗
PubMed1992

Differences in optokinetic and vestibular ocular reflex performance in teleosts and their relationship to different life styles.

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10-15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and per-/postrotatory nystagmus lasted about 10-12 s in the goldfish, but only 2-3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a 'goldfish-like' response pattern as well. Ostariophysan species differed in their reflex performance as well. A 'goldfish-like' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Animals↗
PubMed1990

Neural pathway for aggressive display in Betta splendens: midbrain and hindbrain control of gill-cover erection behavior.

Horseradish peroxidase (HRP) was used to identify parts of the presumptive neural pathway for gill cover erection, a behavioral display pattern performed by Siamese fighting fish (Betta splendens) during aggressive interactions. Motor, motor integration and sensory areas were identified in the medulla and mesencephalon. Motor neurons of the dilator operculi muscle, the effector muscle for gill cover erection, are located in the lateral and medial parts of the caudal trigeminal motor nucleus. Iontophoretic injections of HRP into the lateral trigeminal motor nucleus resulted in labeled cell bodies in two motor areas (medial part of the trigeminal motor nucleus, anterior part of the motor nucleus of cranial nerve IX-X), two parts of the reticular formation (medial and inferior reticular areas), and two nuclei of the octavolateralis system (nucleus medialis, magnocellular octaval nucleus). The HRP injections in the medial part of the caudal trigeminal motor nucleus resulted in labeled cells in the lateral part of the nucleus and in the medial reticular nucleus. Discrete injections of HRP into nucleus medialis revealed a strong axonal projection that terminated in the torus semicircularis. The medial reticular area and both of the octavolateralis nuclei received projections from their contralateral counterparts. Connections between motor areas, and between parts of the reticular formation, may coordinate the performance of gill cover erection with other behavioral patterns used during aggressive display. Connections with the octavolateralis system may provide information on the strength of an opponent's tail beats via the lateral-line system, as well as vestibular information about the fish's own orientation during aggressive display. The organization of inputs to the trigeminal motor nucleus in Betta, a perciform fish, was found to differ from that reported in the common carp, a cypriniform fish. These differences may underlie the different behavioral capabilities of the two groups of fish.

Afferent Pathways↗
PubMed2004

Identification and characterization of a glucagon receptor from the goldfish Carassius auratus: implications for the evolution of the ligand specificity of glucagon receptors in vertebrates.

The structural basis of ligand selectivity of G protein-coupled receptors for metabolic hormones has been an area of intense investigation, and yet it remains unresolved. One approach to delineating the mechanism of ligand-receptor interactions is to compare the ligand specificities of receptors expressed in species that emerged at different times within vertebrate evolution. In this paper we describe the isolation, functional, and phylogenetic characterization of the glucagon receptor from the goldfish Carassius auratus (Teleostei, order Cypriniformes), and compare its ligand specificity with that of the homologous rat receptor. Goldfish (gf) glucagon stimulated glucose production in a dose-dependent manner from isolated goldfish hepatocytes, resulting in 5-fold increase at 1 microm. The goldfish glucagon receptor (gfGlucR) shares 56, 51, 50, and 52% amino acid identities with frog Rana tigrina regulosa, mouse, rat, and human glucagon receptors, respectively. In competitive binding experiments, the recombinant gfGlucR displays high affinity toward goldfish, zebrafish, and human glucagons (IC(50) = 0.6, 9, and 13 nm, respectively) but not toward goldfish glucagon-like peptide-1 or human glucagon-like peptide-1 (7-36) amide. Whereas both goldfish and human glucagons stimulated dose-dependent increases in intracellular cAMP through the recombinant gfGlucR, the recombinant rat GlucR interacted only with human glucagon, analogous to the specificity of the previously characterized glucagon receptor from the frog R. tigrina regulosa. Our results demonstrate that the binding pocket of gfGlucR can accommodate a broad range of glucagon structures and that in the frogs and mammals, there is a structural switch to a more restrictive conformation of glucagon receptors.

Amino Acid Sequence↗
PubMed1994

THE RELATIONSHIP BETWEEN THE LENGTH OF THE CUPULAE OF FREE NEUROMASTS AND FEEDING ABILITY IN LARVAE OF THE WILLOW SHINER GNATHOPOGON ELONGATUS CAERULESCENS (TELEOSTEI, CYPRINIDAE)

Free mechanosensory neuromasts of larval fishes have been described as playing a complementary role to vision in feeding behaviour (Disler, 1971; Iwai, 1972a,b). In certain species or under limited conditions, free neuromasts play a major role in detecting prey. The larvae of mottled sculpin Cottus bairdi can feed on Artemia in the dark by using free neuromasts (Jones and Janssen, 1992). Artificially blinded surface-feeding Aplocheilus lineatus can detect insects on the water surface by means of free neuromasts (Muller and Schwarts, 1982; Tittel et al. 1984; Bleckmann, 1988; Bleckmann et al. 1989). Furthermore, vibrations produced by swimming crustaceans are known to be a potent natural stimulus for the lateral line system in the Antarctic fish Pagothenia borchgrevinki (Montgomery and Macdonald, 1987; Montgomery, 1989). We found that larvae of a plankton feeder, the willow shiner Gnathopogon elongatus caerulescens (Sauvage) (Cypriniformes, Cyprinidae), fed on nauplii of Artemia in complete darkness. Ototoxic compounds, such as streptomycin, have been shown to disturb the function of the lateral line organ or free neuromasts (Kaus, 1987; Blaxter and Fuiman, 1989; Janssen, 1990; Jones and Janssen, 1992). Willow shiner larvae treated with streptomycin sulphate no longer feed on Artemia in the dark (Y. Mukai, in preparation). The willow shiner inhabits calm lakes and feeds on zooplanktonic prey (Nakamura, 1949). The larvae show a high sensitivity to minute water displacements. From these observations and from our findings, it appears that larval willow shiner must feed on zooplankton by using free neuromasts in the dark. In larval willow shiner, the vane-like cupulae of the free neuromasts protrude from the body surface and the long cupulae are 100-250 microm in length (Mukai and Kobayashi, 1991). The prey is detected by the free neuromasts as a result of a slight bending of the cupula in response to local water movements. The shape of the cupula, especially its length, must therefore be related to the sensitivity of the free neuromast, as inferred from the results of Coombs and Janssen (1989) and van Netten and Kroese (1989).

Journal Article↗
PubMed2004

Duplicated receptors for VIP and PACAP (VPAC1R and PAC1R) in a teleost fish, Fugu rubripes.

Two principal groups of receptors orthologous with human PAC1R and VPAC1R and were identified and characterised at the genomic level in the teleost fish Fugu rubripes. An additional group orthologous with VPAC2R was also identified and partially characterised. In Fugu, gene duplication of each of the PAC1Rs, VPAC1Rs and VPAC2Rs appears to have occurred. The topology of the tree surrounding the Fugu duplications and other isolated piscine sequences indicates that the duplication events for these six genes clearly preceded the speciation event leading to the Cypriniformes and Tetraodontiformes and is probably teleost-specific. Overall, the combined pattern of gene expression for each pair of duplicated genes mirrored the expression in other vertebrates. However, within each pair of duplicates further specialisation had occurred, with each demonstrating differential tissue distribution profiles suggesting they that may be responsible for the divergent action of the ligands, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP). The Fugu VPAC1R gene regions showed conserved synteny with human chromosome 3p21.3 and also C. elegans chromosome X, indicating that the putative ancestral human chromosome 3 region may be equivalent to chromosome X in Caenorhabditis elegans.

Amino Acid Sequence↗
PubMed2001

Possible involvement of nitric oxide in signaling pigment dispersion in teleostean melanophores.

The possible involvement of nitric oxide (NO) in regulating the motile activities of teleostean melanophores was studied in the dark chub Zacco temmincki (Cyprinidae, Cypriniformes) and in the translucent glass catfish Kryptopterus bicirrhis (Siluridae, Siluriformes). NO donors, including (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexaneamide (NOR1), molsidomine (MSD), sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), had no pigment-aggregating action on melanophores, but actively dispersed melanosomes in those cells. Among those reagents, NOR 1, a spontaneous releaser of NO, was the most effective. Inhibitors for nitric oxide synthase (NOS), i.e. N omega-nitro-L-arginine methyl ester (L-NNA), N omega-nitro-L-arginine (L-NAME) and N omega-monomethyl-L-arginine (L-NMMA), showed melanosome-aggregating effects. A membrane-permeable analogue of cyclic guanosine-3',5'-monophosphate (8-Br-cGMP) was effective in dispersing melanosomes. The sum of these results suggests that NO plays an active role in the elaborate control of color changes in teleosts by dispersing pigment in melanophores via activation of soluble guanylyl cyclase to increase cytosolic levels of cGMP.

Animals↗
PubMed1999

Species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidae) from cyprinid fishes in North America.

A taxonomic study of Proteocephalus species parasitizing cyprinid fishes in North America, namely Proteocephalus ptychocheilus Faust, 1920 and Proteocephalus cobraeformis Haderlie, 1953, has demonstrated their conspecificity with Proteocephalus torulosus (Batsch, 1786), a common parasite of cypriniform fishes (Cyprinidae and Cobitidae) in the Palaearctic Region. Proteocephalus ptychocheilus and P. cobraeformis are considered junior synonyms of P. torulosus.

Animals↗
PubMedDate not supplied

[Distribution of coccidians (Sporozoa: Coccidiida) in various systematic groups of fishes].

There are about 250 coccidian species associated with fishes. They belong to 8 genera (Calyptospora, Cryptosporidium, Crystallospora, Eimeria, Epieimeria, Goussia, Isospora, Octosporella) and 3 families (Calyptosporidae, Cryptosporidiidae, Eimeriidae). Two genera are represented by great number of species associated with fishes: Eimeria--157 and Goussia--69 species. Most diverse fauna of coccidians was found in fishes of the class Actinopterigii; fishes of the class Elasmobranchii have significantly less number of coccidians. These parasites have never been recorded on the class Holocephali. Coccidian have been recorded in 55 orders of fishes. Within the Actinopterigii, the richest coccidian fauna is recorded from Cypriniformes and Perciformes. Accumulated data on host associations proves that coccidian species have mainly a restricted hosts specificity.

Animals↗
PubMed2001

The ultrastructure of spermatozoa of the slender catfish Silurus microdorsalis (Teleostei, Siluriformes, Siluridae) with phylogenetic considerations.

The spermatozoa of the slender catfish Silurus microdorsalis examined using transmission and scanning electron microscopy are characterized by a tubular structure and the absence of axonemal fins. Their characteristics can be considered to represent a valid symplesiomorphy uniting the Siluridae and taxon-specific for this family. The tubules of Silurus spermatozoon are not observed in the other siluroids. Unusual tubules occur in Citharinus spermatozoa of Characiformes. In addition, there is a considerable similarity in the absence of axonemal fins between Siluridae and Characiformes. Thus the two shared characteristics provide strong evidence that there exists a phylogenetic link between Characiformes and Siluriformes. Silurus appears to be plesiomorphic in having lost the axonemal fins while retaining the tubules in midpiece. The spermatozoa of S. microdorsalis are similar to those of other siluroids having a spherical head with a deep nuclear fossa, a short midpiece and an elongated tail. However, there are some differences between Silurus and other siluroids in the orientation of the centrioles, the number of the mitochondria and the axonemal fins, and minor differences between S. microdorsalis and S. asotus, in particular the orientation of the centriolar complex, and the arrangement of the tubules and the mitochondria in the midpiece. The deep nuclear fossa represents a synapomorphy uniting the Siluriformes, while the shallow nuclear fossa and the absence of axonemal fins are shared by two orders, Characiformes and Cypriniformes.

Animals↗
PubMed2002

Immunohistochemical study of the endocrine cells in the pancreas of the carp, Cyprinus carpio (Cyprinidae).

The regional distribution and relative frequency of some endocrine cells in the pancreas of the carp, Cyprinus carpio Linnaeus, belonging to the family Cyprinidae in the order Cypriniformes, were observed using specific mammalian antisera against insulin, glucagon, somatostatin and human pancreatic polypeptide (hPP) by peroxidase antiperoxidase (PAP) method. The pancreas was divided into four regions (principal and secondary islets, exocrine and pancreatic duct regions). In addition, the pancreatic islet regions were further subdivided into three regions (central, mantle and peripheral regions) and the pancreatic duct regions were subdivided into two regions (epithelial and subepithelial regions). Spherical to spindle or occasionally round to oval shaped immunoreactive (IR) cells were demonstrated in the pancreatic islets, exocrine and pancreatic duct. In the principal islet regions, some cells were also detected in the other regions, most of insulin- and somatostatin-IR cells were located in the central regions, and glucagon- and hPP-IR cells were situated in the peripheral regions. In this regions, insulin-IR cells were most predominant cell types and then, glucagon, somatostatin and hPP in that order. In the secondary islet regions, the regional distribution and relative frequency of these four types of endocrine cells were quite similar to those of the principal islets except for cell clusters consisted of hPP-IR cells that were situated in the peripheral to mantle regions. In the pancreatic duct regions, all four major pancreatic endocrine cells were demonstrated in the inter-epithelial cells and/or basal regions of the epithelial linning. In addition, cell clusters composed of numerous insulin-, moderate glucagon- and somatostatin-IR cells of low frequency were also observed in the subepithelial regions of the pancreatic duct. In the exocrine regions, insulin-, glucagon-, somatostatin- and hPP-IR cells were located in the inter-acinus regions with rare, a few, moderate and moderate frequencies, respectively. In conclusion, the regional distribution and relative frequency of four major pancreatic endocrine cells, insulin-, glucagon-, somatostatin- and hPP-IR cells, in the pancreas of the carp showed general patterns which were observed in other stomachless teleost. However, some species- dependent different distributional patterns and/or relative frequencies were also demonstrated.

Animals↗
PubMed2005

[Phylogeny of chinese catfishes inferred from mitochondrial cytochrome b sequences].

The mitochondrial DNA cytochrome b gene was sequenced from 27 catfish species representing 11 families and 24 genera catfishes in China. Aligning with cytochrome b sequences of eight catfish species from North America and Africa retrieved from GenBank, and selecting Astyanax mexicanu, Cyprinus carpio, and Sardinops melanostictus as outgroups, we constructed a matrix of 38 DNA sequences. The phylogenetic trees were constructed by using Bayesian method and Maximum Parsimony (MP) method. The results showed that (1) there are three base pair deletions of mitochondrial cytochrome b gene compared with Characiformes, Cypriniformes, and Clupeiformes; (2) the representatives of Chinese catfish species form a monophyletic group; and (3) the molecular phylogenetic trees constructed with both methods suggest that the families Sisoridae, Akysidae and Amblycipitidae form a monophyletic group, and the families Clariidae, Schilbidae, Ariidae, Ictaluridae, Cranoglanididae, Pangasiidae, Siluridae, Claroteidae, and Bagridae also form a monophyletic group. The families Cranoglanididae from China and Ictaluridae from North America form a sister-group relationship, and the families Clariidae, Ictaluridae, Siluridae, and Sisoridae are obviously monophyletic groups. But the position of the family Plotosidae was not resolved by Bayesian analysis and maximum parsimony inference.

Animals↗
PubMed2006

Rhabdochona kharani sp. n. (Nematoda: Rhabdochonidae) from the fish Labeo gedrosicus Zugmayer, 1912 from Garruk, District Kharan, Balochistan, Pakistan.

A new nematode species, Rhabdochona kharani sp. nov., has been isolated from the intestine, stomach and swim bladder of the fish Labeo gedrosicus Zugmayer, 1912 (Fam. Cyprinidae: Cypriniformes) from spring water at Garruk, District Kharan, Balochistan. The new species is characterized largely by the presence of eight anterior teeth in the prostom, inconspicuous deirids, by the shape and length of unequal spicules (0.08 - 0.09 and 2.9 - 3.1 mm), and by 17-18 pairs of caudal papillae including 6-7 postanal, one adanal, and 10 -11 preanal. Other characteristics include a pointed tail tip, non filamented eggs, a bulbous, voluminous, vaginal complex that is directed backward, and a vulva that is post-equatorial with a triangular large anterior lip and a smaller posterior lip.

Animals↗
PubMed1991

[Electron microscopic observation of synaptonemal complexes in spermatocytes of six species of fishes].

The synaptonemal complexes (SCs) in spermatocytes of six species of fishes were detected with a combination of surface spreading and silver staining technique and observed under both light and electron microscopes. These fishes are Tilapia nilotica, T. mossambica and Mastacembelus sinensis of Perciformes. Sarcocheilichthys nigripinnis, Pseudorasbora parva and Hemibarbus maculatus of Gobioninae in Cypriniformes. The formation of SCs started in Zygotene and completed at Pachytene. During the pachytene, each SC was morphologically intact, preferentially stained and attached to the nuclear envelope by a dense terminal plaque. Interlock in SCs frequently occurred in Zygotene. In several cases breakage and disentangling of interlocked lateral elements were observed. SCs disappeared in diplotene. The pairing of the SCs started at telomeres and stretched towards kinetochore. The sex determination of Mastacembelus sinensis was xx/xy. The X and Y chromosomal SCs' axes had a distinctive morphology at pachytene and were clearly distinguishable from autosomal SCs. The X and Y chromosomes begain to pair at early pachytene. The X and Y chromosome axes paired to form a length of SC that is somewhat longer than the unpaired portion at the mid-pachytene. There was a dense substance at unpaired portion. Quantitatine evaluation demonstrated that relative length and arm ratio were distinctive characteristics for each autosomal SC. The consistency of relative length and arm ratio indicates the stability of the techniques. The idiograms of SC karyotypes of three species (Tilapia niloticus, T. mossambicus and Mastacembelus sinensis) have been constructed.

Animals↗