Bone lipids of marine fishes.

Assessment of candidates for investigation of bone lipid metabolism yielded the following findings. (1) A tropical marine butterflyfish, Chaetodon ornatissimus, had oil-filled bones (66-80% lipid, percent dry weight) hence may be a suitable condidate. (2) The tropical marine fishes Exallias brevis, Pomacentrus jenkensi, and Chromus agilis, and a Canadian fish Sebastes ruberrimus, had intermediate quantities of oil in their bones (12-49% lipid). (3) In all the foregoing species the major bone lipid was triglyceride, usually more abundant in skull than spine. Sterol and phospholipid were also present. (4) The major fatty acids of the triglycerides (and phospholipids) were 16:0, 18:0, 18:1, and C20, C22 acids. Those acids were dominated by 20:4, 20:5, 22:5, and 22:6. (5) There was more total unsaturation in the bone lipids of S. ruberrimus (from 10 degrees C water; 67-72% unsaturation) compared to the tropical fish (from 25 degrees C water; 32-67% unsaturation) with the exception of E. brevis. (6) One of the tropical species (Arothron meleagris) and a Canadian Chimaeran (Hydrolagus colliei) contained only 1-3% lipid in their bones.     

Chromosome numbers of fishes. I

The published chromosome numbers for 208 temperate and tropical freshwater fishes have been compiled in alphabetical order within the families. This facilitates the work for ichthyologists interested in the karyotype(s) of a particular species, genus or family as well as giving an overall account of the basic chromosome numbers and karyological trends in fishes.     

Extracellular calcium-sensing receptors in fishes.

The extracellular calcium-sensing receptor (CaSR) in fishes, like the CaSRs of tetrapod vertebrates, is a dimeric seven transmembrane, G protein-coupled receptor. The receptor is expressed on the plasma membranes of a variety of tissues and cells where it functions as a sensor of extracellular calcium concentration ([Ca(2+)](o)) in the physiological range. In the context of systemic calcium homeostasis, CaSR expressed in endocrine tissues that secrete calciotropic and other hormones (pituitary gland and corpuscles of Stannius) may play a central role in global integrative signaling, whereas receptor expressed in ion-transporting tissues (kidney, intestine, gills, and elasmobranch rectal gland) may have local direct effects on monovalent and divalent ion transport that are independent of endocrine signaling. In fishes, specifically, CaSR expression at the body surface (at the gills and olfactory tissues, for example) may permit direct sensing of environmental Ca(2+) and Mg(2+) concentrations, especially in the marine environment. Additionally, CaSRs may have other widespread and diverse roles in extracellular Ca(2+) sensing related both to organismal calcium homeostasis and to intercellular Ca(2+) signaling. As a consequence of the broad spectrum of recognized ligands, including polyvalent cations and amino acids, and of binding site shielding by monovalent cations, additional receptor functionalities related to salinity and nutrient detection are proposed for CaSRs. CaSR expression in the gastrointestinal tract may be multifunctional as a sensor for polyvalent cations and amino acids. Structural and phylogenetic analyses reveal strongly conserved features among CaSRs, and suggest that calcium sensing by mammalian parathyroid gland-type CaSR proteins may be restricted to chordates. Comparative functional and genomic studies that include piscine CaSRs can be useful model systems for testing existing hypotheses regarding receptor function, and will shed light on the evolutionary developmental history of calcium homeostasis in the vertebrates.     

Digestive enzymes of three teleost fishes.

The activity of amylase, sucrase, protease and lipase has been examined in Wallago attu, Clarias batrachus and Labeo rohita. The optimum pH value for carbohydrases ranges from 5.0 to 7.0 and that for trypsin between pH 6.8 and 7.8. Lipase is active at a slightly more alkaline medium. The optimum pH for a given enzyme varies in different sections of the alimentary canal of the same fish and also from species to species. Variations are also found in the optimum substrate concentration for a given enzyme in the different sections of the alimentary canal. The activity of carbohydrases is higher in the herbivorous fish Labeo, than in the carnivorous fish Wallago, and the omnivorous fish Clarias. As for protease, maximum activity is found in Wallago. The difference is not so well marked for the activity of lipase. There is a correlation between the normal diet of the fishes and the relative activity of the digestive enzymes.     

A new hemogregarine from marine fishes.

Haemogregarina uncinata sp. n. is described from the blood of 2 marine eelpouts, Lycodes lavalaei and Lycodes vahlii (Perciformes: Zoarcidae). Erythrocytic schizogony occurred in peripheral and cardiac blood, but mature schizonts were restricted to the latter site. Mature and rupturing schizonts contained 10 to 30 merozoites, which were short and thick in small schizonts while slender and long in larger schizonts. Gametocytes developed in mature erythrocytes and displayed morphologic and morphometric characters that distinguished them from other species described. Syzygy and gamete formation occurred in the gut of a leech, Johanssonia sp. Each microgametocyte produced up to 4 apparently nonflagellated gametes. Oocysts developed intracellularly in the epithelial wall of the intestine and at maturity produced under 100 sporozoites from (apparently) several germinal centers. Sporozoites subsequently migrated to the probosces of the leeches. The failure to transmit the parasite to a sculpin (Myoxocephalus octodecemspinosus) and 3 Atlantic cod (Gadus morhua) via regurgitation by the leeches might be indicative of host specificity.     

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.     

Monogenea of Chinese marine fishes. XIV. Two new species of Microcotylidae from fishes of the South China Sea

Two new species of microcotylid monogeneans are described. Solostamenides platyorchis n. sp. was obtained from the gills of Mugil cephalus (Mugilidae) and Polylabroides guangdongensis n. sp. from the gills of Sparus macrocephalus, S. berda and Acanthopagrus latus (Sparidae). Solostamenides platyorchis is morphologically similar to S. mugilis (Vogt, 1878) Unnithan, 1971 and S. pseudomugilis (Hargis, 1956) Unnithan, 1971 in the structure of the copulatory organ, but differs from them in the number, arrangement and shape of the testes. Features of P. guangdongensis distinguishing it from other species of the genus include a copulatory organ lacking small spines and an extremely long polar filament on the egg. In view of this species, we suggest omitting the presence of small spines on the copulatory organ as a diagnostic character of the genus Polylabroides Mamaev & Parukhin, 1976.     

濒危鱼类

报道了国内外18种著名的濒危鱼类、分析了濒危原因,提出了保护措施和建议。     

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.