Faunal structure of Japanese freshwater fishes and its artificial disturbance

The hierarchical structure of areas of endemicity of freshwater fishes in the Japanese Archipelago was analyzed using parsimony analysis of endemicity (PAE) and its modification. Supporting the results of previous studies, the present analysis, which includes species, subspecies, intraspecific monophyletic lineages, and/or hypothetical ancestors, revealed the uniqueness of the local ichthyofauna in northeastern Hokkaido, large changes in ichthyofauna across the Fossa Magna region, central Honshu, and some additional new patterns. A split network analysis was used to represent the complex relationships among local faunas in the archipelago and also in East Asian regions. Artificially disturbed fish faunas have recently lost part of their original endemic areas, producing a remarkable ??homogenization?? among local faunas (+9.0% in Jaccard??s similarity coefficient). The majority of this homogenization can be explained by introduction of domestic species (+8.6%), especially from Lake Biwa, the largest lake in Japan.     

The prevalence of Trypanosoma catostomi in white sucker (Catostomus commersoni) from southern Ontario.

During the summer of 1975, 285 white suckers (Catostomus commersoni) from 10 localities in southern Ontario were examined for trypanosomes. Trypanosoma catostomi Daly and DeGiusti, 1971 was found in the blood of 11.6% of the fish examined using the haematocrit centrifugation technique. Infected juvenile fish (33%) and infected adult fish (4%) were found in 6 of 10 locations.     

The specificity of Helicoverpa armigera stunt virus infectivity.

Helicoverpa armigera stunt virus (HaSV) is a member of the Tetraviridae family of RNA viruses whose replication and expression strategies are not well understood due to the absence of an in vitro cell culture system. We set out to find such a system for HaSV by screening an array of 13 insect and 1 mammalian cell culture lines with both virus particle infection and genomic RNA transfection. No cell line was found to be permissive for replication, although entry of genomic RNA was verified. The apparent specificity of this virus for its in vivo midgut target site was strongly corroborated by studies involving Northern blots of RNA extracted from infected insects. Only larval midgut RNA showed the presence of virus after hosts were infected per os or by injection which exposed other host cell types to the virus. The absence of replication in cell culture was due to a lack, or presence, of host factors important to replicase activity and also the likely absence of virus particle binding and entry. We thus provide both in vitro- and in vivo-based evidence demonstrating that this virus is extremely specific in the type of cells in which it will initiate an infection.     

Ecological speciation in marine v. freshwater fishes

Absolute barriers to dispersal are not common in marine systems, and the prevalence of planktonic larvae in marine taxa provides potential for gene flow across large geographic distances. These observations raise the fundamental question in marine evolutionary biology as to whether geographic and oceanographic barriers alone can account for the high levels of species diversity observed in marine environments such as coral reefs, or whether marine speciation also operates in the presence of gene flow between diverging populations. In this respect, the ecological hypothesis of speciation, in which reproductive isolation results from divergent or disruptive natural selection, is of particular interest because it may operate in the presence of gene flow. Although important insights into the process of ecological speciation in aquatic environments have been provided by the study of freshwater fishes, comparatively little is known about the possibility of ecological speciation in marine teleosts. In this study, the evidence consistent with different aspects of the ecological hypothesis of speciation is evaluated in marine fishes. Molecular approaches have played a critical role in the development of speciation hypotheses in marine fishes, with a role of ecology suggested by the occurrence of sister clades separated by ecological factors, rapid cladogenesis or the persistence of genetically and ecologically differentiated species in the presence of gene flow. Yet, ecological speciation research in marine fishes is still largely at an exploratory stage. Cases where the major ingredients of ecological speciation, namely a source of natural divergent or disruptive selection, a mechanism of reproductive isolation and a link between the two have been explicitly documented are few. Even in these cases, specific predictions of the ecological hypothesis of speciation remain largely untested. Recent developments in the study of freshwater fishes illustrate the potential for molecular approaches to address specific questions related to the ecological hypothesis of speciation such as the nature of the genes underlying key ecological traits, the magnitude of their effect on phenotype and the mechanisms underlying their differential expression in different ecological contexts. The potential provided by molecular studies is fully realized when they are complemented with alternative (e.g. ecological, theoretical) approaches.     

Determinants of host-specificity in parasites of freshwater fishes.

Factors responsible for interspecific variability in host-specificity were investigated within 15 genera (including 176 species) of metazoan parasites found in Canadian freshwater fish. For each species in a genus, the parasite's number of known hosts was determined from published host-parasite records. The effects of the total number and mean size of potential hosts (i.e. all fish species belonging to the family or families that include a parasite's known hosts) on number of hosts of congeneric species were evaluated using multiple regressions. Since parasite species that have been recorded often tend to have greater numbers of known hosts than do seldom-recorded parasites, it was necessary to control for the confounding effect of study intensity. In all parasite genera, whether from highly specific taxa such as monogeneans or from less host-specific ones, there was a positive relationship between the number of potential hosts and the number of known hosts. However, no consistent relationships were observed between the mean size of potential hosts and number of known hosts. These results suggest that the availability of suitable host species may have been a key factor limiting the colonization of new hosts by fish parasites.     

Substrate specificity of the Trypanosoma cruzi trans-sialidase.

Trypanosoma cruzi trypomastigotes acquire sialic acid (SA) from host glycoconjugates by means of a plasma membrane-associated trans-sialidase (TS). Here we study the substrate specificity of TS, which differs from all known sialyltransferases in that it does not require cytidine monophosphate (CMP)-SA as donor. The T. cruzi TS reversibly transfers SA to saccharides with terminal beta-Gal (but not alpha-Gal) residues. Donors are saccharides with SA linked to terminal beta-Gal residues by (alpha 2-3), but not (alpha 2-6) bonds. The type of beta-linkage of the terminal Gal residue is of minor importance (beta 1-4 and beta 1-6 are slightly better than beta 1-3), whereas chain length and the structure of additional vicinal sugar residues are not relevant. SA on the surface of living trypomastigotes of T. cruzi is transferred back and forth between the parasite surface and acceptor molecules with terminal beta-Gal, either in solution or on the surface of neighbouring mammalian cells. Addition of fucose residue on or close to the terminal galactose impairs TS activity. As a consequence, the enzyme acts poorly on the E-selectin ligand sialyl-Lewisx and its precursor Lewisx, and in vitro adhesion of TS-treated neutrophils to L-cells expressing L-selectin is not affected. Modifications in the structure of the (alpha 2-3)-linked N-acetyl-neuraminic acid (Neu5Ac) (deoxy or methoxy) of the donor molecules do not impair transfer if the changes are at C9, whereas changes at C4, C7 and C8 impair the ability to donate the modified SA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nutrient and energy content of freshwater fishes

The analyses of fresh total body homogenates of 2385 freshwater fishes from 17 species originating in natural waters and aquaculture facilities resulted in average values of 19.1–37.8% dry matter, 13.6–18.3% crude protein, 0.8–18.3% crude fat, 0.16–2.17% nitrogen-free extracts (NFE), 2.2–2.9% nitrogen and 0.39–1.02% phosphorus. The gross energy content ranged from 3.83 to 11.49 MJ/kg. With increasing fat content in the fishes, water content decreased and dry matter content increased. Through this interdependence, a significant correlation was found between dry matter and crude fat and energy content (r²=0.92–0.97). The values of crude protein, crude ash, NFE, nitrogen and phosphorus did not show any significant influence on dry matter content (r²=0.0005–0.46). Based on the significant correlation between dry matter and gross energy (gross energy [MJ/kg]=0.0253 dry matter [%]^1.6783), the energy content of freshwater fishes can easily be estimated by the dry matter content in the total body.     

Trypanosoma brucei: infectivity and immunogenicity of cultured parasites

Trypanosoma brucei brucei, derived from the salivary glands of infected tsetse flies (Glossina morsitans morsitans) and maintained in culture for over 4 years, were infective to both albino rats and tsetse flies. Virulence was markedly enhanced during the first passage in albino rats or tsetse flies. Irradiated cultured trypanosomes induced immunity to homologous challenge but not to tsetse fly or blood-induced challenge with the same stock.     

DNA barcoding to characterize biodiversity of freshwater fishes of Egypt

Molecular Biology Reports - The current study represents the first molecular characterization of freshwater fish species in Egypt from two major fish resources; the River Nile and Lake Nasser. A...     

Geographical distribution of African freshwater fishes

Geographical distribution of African freshwater fishes is discussed with emphasis on the effects of major continental features, hydrographic history, and Pleistocene climatic fluctuations. Differences in the modes of dispersal and biological interactions among various categories of fishes, ecological as well as phyletic, have also had marked effects on distribution.
The African continent can be divided into ten ichthyofaunal provinces. The geography of these provinces and composition of their fish faunas is briefly described. The paper concludes with a consideration of the faunistic relationships of African lakes with endemic fishes.     

Reproductive ecology of Brazilian freshwater fishes

We used metadata on nine reproductive traits of 67 species of Brazilian iteroparous, oviparous, teleost freshwater fishes to test phenotypes associations to discriminate species that only spawn in large rivers (lotic fishes) from those capable to spawn in lentic habitats (lentic fishes). We tested the hypothesis that lotic fishes present spawning migration, shorter spawning season, single spawning, no parental care, free eggs, higher relative fecundity, faster embryogenesis, and larger size, while lentic fishes present no spawning migration, longer spawning season, multiple spawning, parental care, adhesive eggs, lower relative fecundity, slower embryogenesis, and smaller size. Our analyses supported the hypothesis but not all phenotypic associations satisfied it, specifically with regard to lentic fishes or to pairs of phenotypes typical of lentic fishes. We also concluded that spawning in large rivers is a better predictor of bionomic characters than spawning in lentic habitats, and lotic fishes are specialists compared to lentic fishes.