Characiform Fish Research Articles

Annulotrematoides bryconi sp. n. (Monogenea: Dactylogyridae) parasitic on Brycon cephalus (Osteichthyes: Characidae) from Brazil.

Annulotrematoides bryconi sp. n. is described and illustrated from specimens collected from gills of characiform fish, Brycon cephalus (Günther, 1869), in pisciculture ponds from Pirassununga, São Paulo, Brazil. Diagnostic characters of the new species are the tegument of trunk showing annulations, except on the cephalic regiona, and copulatory complex comprising sclerotized male copulatory organ coiled in 1 1/2 rings. This is the first record of monogeneans parasitic on the gills of B. cephalus.

A new Eocene citharinoid fish (Ostariophysi: Characiformes) from Tanzania

ABSTRACT A single specimen of the anterior portion of a small fish was collected from the Eocene Mahenge site of Tanzania in 1996. The specimen, preserved as part and counterpart natural mold, is identified as belonging to a characiform fish, although the presence of a Weberian apparatus has not been confirmed beyond doubt. Features of the bones, such as the prominent lateral ridge on the anterodorsal corner of the opercle, the fused postcleithra 2+3, and the lack of a dentary symphyseal hinge, indicate that the fish is related to the Citharinidae and Distichodontidae. The fossil cannot be included in any known genus, and is described here as a new genus and species, Eocitharinus macrognathus. The fossil record of characiforms includes few articulated skeletons, of which only one had been reported previously from Africa, described in the family Characidae (=Alestidae).

Nuclear DNA content determination in Characiformes fish (Teleostei, Ostariophysi) from the Neotropical region

In the present study, nuclear DNA content was analyzed in 53 species of Characiformes fish from the Neotropical region. Diploid number ranged from 2n = 48 in Astyanax fasciatus, Gymnocorymbus ternetzi and Hyphessobrycon griemi to 2n = 102 in Potamorhina squamoralevis, with a modal number of 54 chromosomes. Nuclear DNA content ranged from 1.70 ± 0.04 pg of DNA per diploid nucleus in Acestrorhynchus pantaneiro to 3.94 ± 0.09 pg in Tetragonopterus chalceus. A general analysis showed a mean value of 2.9 pg of DNA per diploid nucleus. Very similar DNA content values were observed in the species of the family Cynodontidae which showed a variation of 3% between the two genera studied. Small variations were observed between populations of Gymnocorymbus ternetzi, Astyanax fasciatus and Moenkhausia sanctaefilomenae (Characidae, Tetragonopterinae). The subfamilies Tetragonopterinae and Acestrorhynchinae (Characidae) presented the widest range, about 96%. Even in those families in which diploid number and karyotypic formulae were conserved such as the families Anostomidae, Curimatidae, and Prochilodontidae, episodes leading to losses or gains of genetic material became fixed in their evolutionary history.

New cases of supernumerary chromosomes in characiform fishes

Supernumerary chromosomes were described for five species of Neotropical characiform fishes. These extra chromosomes were small, acrocentric and fully heterochromatic in Leporinus friderici from two different localities as well as in Leporinus sp., but metacentric and fully heterochromatic in Cyphocharax modesta and Prochilodus nigricans. In Characidium cf. zebra, this element was small, acrocentric and euchromatic. GC-rich DNA blocks were observed in the supernumerary chromosome of Leporinus sp. using chromomycin A3. The widespread occurrence of these extra chromosomal elements suggests their independent origins.

Ecology of Cichla (Cichlidae) in Two Blackwater Rivers of Southern Venezuela

We investigated the ecology of peacock cichlids (Cichla spp.), diurnal piscovores and important gamefishes, in the Rio Cinaruco (Rio Orinoco drainage of the southern Venezuelan llanos) during the dry seasons of 1992-1993 and the Rio Pasimoni (Rio Negro-Amazonas drainage) during early 1993. In the Cinaruco, three Cichla species partitioned available habitats: C. intermedin near structure in primary river channel within or near swift current, C. orinocensis in shallow water along the shoreline of lagoons or slow channel reaches, and C. temensis in deeper waters along sandbanks and steeper rocky banks of lagoons and the river channel. During the dry season, C. orinocensis and C. temensis fed heavily on small characiform fishes, and C. intermedin consumed a variety of fishes, including loricariid catfishes. Only two peacock cichlids, C. orinocensis and C. temensis, were found in the Pasimoni, a more acidic and less seasonal ecosystem. These two species were larger in the Pasimoni compared with Cinaruco conspecifics; however, conspecifics from the two locations conformed to similar mass-length relationships. In both river systems, C. temensis were significantly larger than congeners, and C. temensis consumed larger prey than congeners in the Cinaruco. Examination of gonads and sizes of intraovarian oocytes indicated that reproduction by all five populations probably is initiated during the late low water period and may continue into the flooding period. Investigamos la ecologia de los pavones (Cichlidae, genero Cichla), picivores diurnos importantes en la pesca deportiva, en el Rio Cinaruco (cuenca del Rio Orinoco en el sur del estado Apure, Venezuela) durante la sequia de los alios 1992-1993, y del Rio Pasimoni (cuenca Rio Amazonas, estado Amazonas) de Venezuela durante los primeros meses del 1993. En el Cinaruco, tres especies de Cichla reparten los habitat disponibles: C. intermedin se ubica cerca de cobertura (arboles sumergidas, etc.) en el cauce principal cerca 0 dentro de la corriente rapida; C orinocensis se

Weight-length relationship and condition of the characiform Triportheus guentheri

The sources of variations in the weight-length relationship parameters, and in the Fulton's, allometric, and relative condition factors (K) of the characiform fish Triportheus guentheri were investigated. The use of these indices as indicators of condition were also discussed. The 2899 females and 2491 males were captured with gill nets from January 1986 to March 1988 in Tres Marias Reservoir (18° 15′ and 45° 15′ W), Brazil. Weight-length relationship parameters varied monthly in both sexes mainly due to the skewness of the relative frequency of the number of fish per body length. This suggests that a selective sample and/or the population length structure may strongly influence the estimate of those parameters. The K showed high correlations (r ≥ 0.99) among themselves. Their variations were ascribed to carcass weight in both sexes when analyzed by month, or to the ovary weights when analyzed by female gonad development intervals. The monthly weight-length relationship parameters of T. guentheri presented low or null correlation with K, except for the female's coefficient of regression. Problems using these parameters as indicators of condition suggested that they are not good indices to express condition. Some restrictions regarding the use of K are discussed.

The radiation of characiform fishes and the limits of resolution of mitochondrial ribosomal DNA sequences.

Phylogenetic relationships among fishes from ostariophysan orders, characiform families, and serrasalmin genera (e.g., "piranhas") were examined using partial mitochondrial ribosomal DNA sequences of the 12S and 16S genes. Phylogenetic information content of these sequences was assessed at three levels of taxonomic inclusiveness by analyzing the patterns of nucleotide substitution using secondary structure models. Conserved and variable regions were identified, mapped onto the structural models, and compared at increasing levels of taxonomic divergence. In general, loop regions (unpaired) exhibited a higher level of variation than did stem regions (paired). A high proportion of compensatory substitutions was observed in stem regions in three data sets, suggesting strong selection to maintain the secondary structure. Saturation due to multiple substitutions was indicated by decreasing transition/transversion ratios and strong structural constraints on variation in comparisons among orders of Ostariophysi but was not obvious among families of Characiformes and was not detected among serrasalmin genera. Reliable phylogenetic signal successfully reconstructed relationships among serrasalmin genera. However, aside from a few well-supported clades, relationships could not be reconstructed with confidence among characiform families and ostariophysan orders. The reciprocal monophyly of African and Neotropical characiform lineages was rejected (based on maximum likelihood ratio tests), and some support for previous hypotheses based on morphology was provided by the molecular data. The radiation of characiform fishes is discussed in a historical biogeographic context.

The Radiation of Characiform Fishes and the Limits of Resolution of Mitochondrial Ribosomal DNA Sequences

The Radiation of Characiform Fishes and the Limits of Resolution of Mitochondrial Ribosomal DNA Sequences

Trends in chromosome evolution of neotropical characiform fishes

SUMMARYNeotropical characiform fishes present two main trends of chromosomal evolution: some taxa show a heterogeneous pattern, with an extensive numerical and structural variation while others show a more homogeneous one, with a clear stability in their karyotype macrostructure. The implications of the populational features and some other conditions to these two general paths are discussed.

Heterochromatin and NORs variability inLeporinusfish (Anostomidae, Characiformes)

SUMMARYC-banding studies in four species of Characiformes fish of the genus Leporinus (Anostomidae) identified interspecific differences despite the strict similarity in karyotype macrostructure among them. A perceptible reduction in centromeric heterochromatin observed in L. piau seems to be a derived condition. L. amblyrhyncus and L. taeniatus exhibit a centromeric and telomeric heterochromatin pattern which is possibly basic in the group, and L. striatus shows a few exclusive intercalary blocks probably derived from inversions and/or transpositions. The nucleolar organizer regions, which were always found to be associated with heterochromatin segments, appear in different chromosomes or chromosome sites in the species studied, also indicating the occurrence of modifications during karyotype evolution in these fish.

Patterns of variation in life history among South American fishes in seasonal environments.

Ten traits related to life history theory were measured or estimated for 71 freshwater fish species from two locations in the Venezuelan llanos. Multivariate statistics and cluster analysis revealed three basic endpoint patterns bounding a two-dimensional continuum. A suite of attributes associated with parental care and aseasonal reproduction appeared to correspond to an equilibrium strategy. A second group of small fishes was distinguished by traits associated with rapid colonizing ability: early maturation, continuous reproduction, and small clutches. The third basic pattern was associated with synchronized reproduction during the early wet season, high fecundity, absence of parental care, and breeding migrations. A subset of mostly small fishes exhibiting little or no parental care, small clutches, and two to four month reproductive seasons was intermediate between the opportunistic (rapidly colonizing) and seasonal strategies. All ten life history variables showed significant effects of phylogeny. The cluster of species corresponding to the equilibrium group was dominated by siluriform fishes and perciforms of the Cichlidae. The opportunistic cluster was dominated by cyprinodontiform and characiform fishes, whereas the seasonal cluster contained primarily characiform and siluriform fishes. Seven of nine traits were significantly correlated with body length. The three reproductive patterns are interpreted as being adaptative with respect to relative intensity and predictability of temporal and spatial variation in abiotic environmental parameters, food availability, and predation pressure.