Parasitic copepods of fishes: a new genus of the Hatschekiidae from New Caledonia,and new records of the Pennellidae,Sphyriidae and Lernanthropidae from the South Atlantic and South Pacific

A new genus and species of the Hatschekiidae, Laminohatschekia synaphobranchi, is described from an eel caught off New Caledonia. It is characterised by its long ribbon-like trunk and by the possession of three pairs of biramous legs. The pennellid Sarcotretes scopeli is redescribed from a macrourid also taken off New Caledonia. Sarcotretes lobatus is recognised as a synonym of S. scopeli. Phrixocephalus carcellesi is described in detail for the first time, from the stomach contents of a King Shag caught in the Falkland Islands. A wide range of individual variability in holdfast structure was noted in P. carcellesi. A new species, Peniculisa bellwoodi, is described from Pomacentrus amboiensis collected at Lizard Island on the Great Barrier Reef. The sphyriid Lophoura cornuta is redescribed from a synaphobranchid eel caught off New Caledonia and both sexes of a lernanthropid, Aethon morelandi, are redescribed from Nemadactylus macropterus in southern Australia.     

The Human Red Cell Voltage-regulated Cation Channel. The Interplay with the Chloride Conductance,the Ca<Superscript>2+</Superscript>-activated K<Superscript>+</Superscript> Channel and the Ca<Superscript>2+</Superscript> Pump

Electrocytes from the electric organ of Electrophorus electricus exhibited sodium action potentials that have been proposed to be repolarized by leak currents and not by outward voltage-gated potassium currents. However, patch-clamp recordings have suggested that electrocytes may contain a very low density of voltage-gated K⁺ channels. We report here the cloning of a K⁺ channel from an eel electric organ cDNA library, which, when expressed in mammalian tissue culture cells, displayed delayed-rectifier K⁺ channel characteristics. The amino-acid sequence of the eel K⁺ channel had the highest identity to Kv1.1 potassium channels. However, different important functional regions of eel Kv1.1 had higher amino-acid identity to other Kv1 members, for example, the eel Kv1.1 S4-S5 region was identical to Kv1.5 and Kv1.6. Northern blot analysis indicated that eel Kv1.1 mRNA was expressed at appreciable levels in the electric organ but it was not detected in eel brain, muscle, or cardiac tissue. Because electrocytes do not express robust outward voltage-gated potassium currents we speculate that eel Kv1.1 channels are chronically inhibited in the electric organ and may be functionally recruited by an unknown mechanism.     

Gelatinous zooplankton (ctenophores,salps and medusae): an important food resource of fishes in the temperate SW Atlantic Ocean

This study quantifies the occurrence of gelatinous zooplankton in the stomach contents of fishes from the southwest Atlantic Ocean (33°–55°S). More than 69,000 fish stomachs belonging to 107 species were examined. A total of 39 fishes were documented as consumers of gelatinous zooplankton, 23 of which were newly discovered. Three gelatinous organism consumption categories are recognized: (1) very frequent consumers (10 species, six of which were exclusive); frequent consumers (five species); and occasional consumers (26 species). Three types of gelatinous prey (ctenophores, salps and medusae) were found in the stomach contents of fishes. Ctenophores were consumed at high levels across almost the entire continental shelves of Argentina and Uruguay. Salps were frequent prey on the slope and southern shelf. In contrast, medusae were consumed in coastal areas, slopes and the southern shelf. Classification methods (group average sorting of the Bray–Curtis similarity measures based on log (X?+?1)-transformed percentage data) determined six areas where fishes predated on gelatinous organisms. SIMPER (similarity percentages) analysis determined which fishes contributed more to the consumption of gelatinous organisms. Results revealed that two fish species (Stromateus brasiliensis and Squalus acanthias) had high gelatinous zooplankton predation rates throughout the entire study area, while another six species (Patagonotothen ramsayi, Helicolenus dactylopterus lahillei, Macrourus holotrachys, Merluccius hubbsi, Schroederichthys bivius, and Macruronus magellanicus), while widely distributed, seemed to have specific areas where consumption occurred. This study not only provides new knowledge about the importance of gelatinous zooplankton in the diet of numerous fishes, but might also be valuable for planning and managing local fisheries.     

Nine polymorphic microsatellite loci in the Neotropical electric eel Eigenmannia (Teleostei: Gymnotiformes)

Ten microsatellite loci were isolated from a species of the Neotropical electric eel, Eigenmannia, a genus of freshwater fish characterized by small populations and low vagility. Nine microsatellites were polymorphic, the number of alleles ranging from seven to 27, and values of observed heterozygosity ranging from 0.327 to 0.741. These loci were developed for population genetic studies of Eigenmannia sp. 2, however, cross‐amplification carried out with other species of this genus as well as other Gymnotiformes genera indicate that these molecular markers are also potentially useful for population‐level studies in closely related species.     

Dietary effects on fatty acid composition in muscle tissue of juvenile European eel, <Emphasis Type="Italic">Anguilla anguilla</Emphasis> (L.)

The role of intracontinental migration patterns of European eel (Anguilla anguilla) receives more and more recognition in both ecological studies of the European eel and possible management measures, but small-scale patterns proved to be challenging to study. We experimentally investigated the suitability of fatty acid trophic markers to elucidate the utilization of feeding habitats. Eight groups of juvenile European eels were fed on eight different diets in a freshwater recirculation system at 20°C for 56 days. Three groups were fed on freshwater diets (Rutilus rutilus, Chironomidae larvae, and Gammarus pulex) and four groups were reared on diets of a marine origin (Clupea harengus, Crangon crangon, Mysis spec., and Euphausia superba) and one on commercial pellets used in eel aquaculture. Fatty acid composition (FAC) of diets differed significantly with habitat. FAC of eel muscle tissue seemed to be rather insensitive to fatty acids supplied with diet, but the general pattern of lower n3:n6 and EPA:ARA ratios in freshwater prey organisms could be traced in the respective eels. Multivariate statistics of the fatty acid composition of the eels resulted in two distinct groups representing freshwater and marine treatments. Results further indicate the capability of selectively restraining certain fatty acids in eel, as e.g. the n3:n6 ratio in all treatments was <4, regardless of dietary n3:n6. In future studies on wild eel, these measures can be used to elucidate the utilization of feeding habitats of individual European eel.     

Occurrence of exotic eels in natural waters of South Korea

We surveyed the proportion of anguillid eel species inhabiting South Korea natural waters. From September 2014 to August 2015, 429 eels were collected in various habitats for identification using morphological features and DNA-based molecular methods. We found 424 Japanese eels (Anguilla japonica, 98.8%), two European eels (A. anguilla, 0.5%), one American eel (A. rostrata, 0.23%), one tropical eel (A. marmorata, 0.23%), and one short-finned eel (A. bicolor pacifica, 0.23%). Three (A. anguilla, A. rostrata, and A. bicolor pacifica) are exotic species to the natural waters of South Korea; this study is the first record of their distribution in this region. Specifically, A. anguilla was found in the Lake Soyang and Cheongpyeong, while A. rostrata was found only in the Lake Cheongpyeong, and A. bicolor pacifica was found in the Geum River estuary.     

New records of two deep-sea eels collected from the Western Pacific Ocean based on COI and 16S rRNA genes

Background

Two deep-sea eels collected from the Western Pacific Ocean are described in this study. Based on their morphological characteristics, the two deep-sea eel specimens were assumed to belong to the cusk-eel family Ophidiidae and the cutthroat eel family Synaphobranchidae.

Methods and results

To accurately identify the species of the deep-sea eel specimens, we sequenced the mitochondrial genes (cytochrome c oxidase subunit I [COI] and 16S ribosomal RNA [16S rRNA]). Through molecular phylogenetic analysis based on mtDNA COI and 16S rRNA gene sequences, these species clustered with the genera Bassozetus and Synaphobranchus, suggesting that the deep-sea eel specimens collected are two species from the genera Bassozetus and Synaphobranchus in the Western Pacific Ocean, respectively.

Conclusions

This is the first study to report new records of the genera Bassozetus and Synaphobranchus from the Western Pacific Ocean based on COI and 16S rRNA genes

     

Effects of eel atrial natriuretic peptide on NaCl and water transport across the intestine of the seawater eel

Summary Eel atrial natriuretic peptide inhibited the serosa-negative transepithelial potential difference and short-circuit current, accompanied by a decrease in NaCl and water absorption across the seawater eel intestine. Similar effects were obtained after treatment with N-terminally truncated eel atrial natriuretic peptide (5–27), indicating that N-terminal amino acids are not essential for the action of eel atrial natriuretic peptide. Although mammalian atrial natriuretic peptides also inhibited the short-circuit current, a 100-fold higher concentration was reuired to obtain the same effect as with eel atrial natriuretic peptide, indicating that eel atrial natriuretic peptide is 100 times as potent in eel intestine as the mammalian atrial natriuretic peptides. Similarly, in mammalian atrial natriuretic peptide, the four N-terminal amino acids had no significant effects. However, when the C-terminal tyrosine was removed, the potency of rat atrial natriuretic peptide was lowered. Compared with the effects of acetylcholine, serotonin and histamine, eel atrial natriuretic peptide was the most potent inhibitor, with 100% inhibition at 10^-7 M; 50% inhibition was obtained at 10^-2 M in acetylcholine, and 30% inhibition in serotonin (10^-5 M) and histamine (10^-3 M). These inhibitory effects of eel atrial natriuretic peptide were not diminished even in the presence of tetradoxin, and were mimicked by 8-bromoguanosine 3,5-cyclic monophosphate. Based on these results, structure-activity relationships of eel atrial natriuretic peptide and a possible mechanism of action of eel atrial natriuretic peptide are discussed.Abbreviations 8BrcGMP 8-bromoguanosine 3,5-cyclic monophosphate - eANP eel atrial natriuretic peptide - hANP human atrial natriuretic peptide - 5-HT 5-hydroxytryptamine creatine sulphate - I _sc short-circuit current - PD transepithelial potential difference - rANP rat atrial natriuretic peptide - R _t tissue resistance - TTX tetrodotoxin     

Grazing by the intertidal fish Anoplarchus purpurescens upon a distasteful polychaete worm

Synopsis Cirratulid worms are common inhabitants of the central California rocky intertidal zone and appear to offer a potentially rich source of food for intertidal fishes. However, analyses of stomach contents revealed that they do not appear in the diets of the commonest intertidal fishes. Apparently only one species, the eel blenny Anoplarchus purpurescens, feeds on cirratulids in significant amounts.Feeding experiments employing local intertidal fishes showed that the common intertidal cirratulid, Cirriformia luxuriosa, is distasteful to most of the fishes. Only two species ate its tentacles, and only A. purpurescens consistently ate large quantities. We propose that C. luxuriosa possesses a predation-deterring chemical similar to that reported in C. spirabrancha, although A. purpurescens apparently has been able to circumvent this anti-predator mechanism.The ability of A. purpurescens to eat Cirriformia tentacles allows it to tap a seemingly little-used food source, and thus may decrease competition between A. purpurescens and other intertidal fishes. This feeding relationship also represents a possible example of coevolution between a predator and its prey.     

Studies of the blood chemistry of Electrophorus electricus and a new physiological saline solution based thereon

Based upon analyses of the composition of electric eel blood serum we suggest a new physiological saline solution as follows: 188 mM NaCl, 5 mM KCl, 2 mM MgCl₂, 2 mM CaCl₂, 0.15 mM NaH₂PO₄, 1.45 mM Na₂HPO₄ and 5 mM glucose; pH 7.4. The major difference between this saline and that used in most of the previous investigations using eel electroplaques is that the total Na⁺ concentration is increased from between 162.7 and 171.7 mequiv/l to 191 mequiv./l. This increase does not appear to affect the electrophysiological properties of the electroplaque.     

The case for sequencing the genome of the electric eel Electrophorus electricus

A substantial international community of biologists have proposed the electric eel Electrophorus electricus (Teleostei: Gymnotiformes) as an important candidate for genome sequencing. In this study, the authors outline the unique advantages that a genome sequencing project of this species would offer society for developing new ways of producing and storing electricity. Over tens of millions of years, electric fish have evolved an exceptional capacity to generate a weak (millivolt) electric field in the water near their body from specialized muscle‐derived electric organs, and simultaneously, to sense changes in this field that occur when it interacts with foreign objects. This electric sense is used both to navigate and orient in murky tropical waters and to communicate with other members of the same species. Some species, such as the electric eel, have also evolved a strong voltage organ as a means of stunning prey. This organism, and a handful of others scattered worldwide, convert chemical energy from food directly into workable electric energy and could provide important clues on how this process could be manipulated for human benefit. Electric fishes have been used as models for the study of basic biological and behavioural mechanisms for more than 40 years by a large and growing research community. These fishes represent a rich source of experimental material in the areas of excitable membranes, neurochemistry, cellular differentiation, spinal cord regeneration, animal behaviour and the evolution of novel sensory and motor organs. Studies on electric fishes also have tremendous potential as a model for the study of developmental or disease processes, such as muscular dystrophy and spinal cord regeneration. Access to the genome sequence of E. electricus will provide society with a whole new set of molecular tools for understanding the biophysical control of electromotive molecules, excitable membranes and the cellular production of weak and strong electric fields. Understanding the regulation of ion channel genes will be central for efforts to induce the differentiation of electrogenic cells in other tissues and organisms and to control the intrinsic electric behaviours of these cells. Dense genomic sequence information of E. electricus will also help elucidate the genetic basis for the origin and adaptive diversification of a novel vertebrate tissue. The value of existing resources within the community of electric fish research will be greatly enhanced across a broad range of physiological and environmental sciences by having a draft genome sequence of the electric eel.     

Global Spread of the Eel Parasite Gyrodactylus Anguillae (Monogenea)

Gyrodactylus anguillae is known from four continents, and intraspecific variation in the morphology of specimens from each continent is negligible. However, morphological characters alone may not always be adequate for recognizing populations that have been isolated geographically over evolutionary time. We were unable to obtain specimens from Northeast Asia, but G. anguillae collected from North America, Europe and Australia had identical ribosomal DNA sequences (ITS1-5.8SrRNA-ITS2 region). This lack of even minor genetic variation in populations from three remote continents leads us to conclude that they share a contemporary common ancestor. This is one of at least five pests of eels to have invaded new continents as a result of the eel trade in the last four decades; these other known eel pests include Pseudodactylogyrus spp. (Monogenea) and Anguillicola spp. (Nematoda). Their dispersal has probably been secondarily augmented by longshore migration of infected eels, and perhaps also by transportation in ballast waters. The only other known gyrodactylid from eel gills, G. nipponensis from Japanese eel, is not closely related to G. anguillae, because the ITS1 region of the former is short (370 bases) and that of the latter long (685 bases). G. anguillae probably originated in Europe, because it was recorded there over 40 years ago, before the development of the international eel trade. We predict that the worm has a high potential to invade eel populations in East Africa, Southeast Asia, and New Zealand.     

Kinetics of Water Transport in Eel Intestinal Vesicles

Brush border membrane vesicles, BBMV, from eel intestinal cells or kidney proximal tubule cells were prepared in a low osmolarity cellobiose buffer. The osmotic water permeability coefficient P _f for eel vesicles was not affected by pCMBS and was measured at 1.6 × 10⁻³ cm sec⁻¹ at 23°C, a value lower than 3.6 × 10⁻³ cm sec⁻¹ exhibited by the kidney vesicles and similar to published values for lipid bilayers. An activation energy E _a of 14.7 Kcal mol⁻¹ for water transport was obtained for eel intestine, contrasting with 4.8 Kcal mol⁻¹ determined for rabbit kidney proximal tubule vesicles using the same method of analysis. The high value of E _a , as well as the low P _f for the eel intestine is compatible with the absence of water channels in these membrane vesicles and is consistent with the view that water permeates by dissolution and diffusion in the membrane. Further, the initial transient observed in the osmotic response of kidney vesicles, which is presumed to reflect the inhibition of water channels by membrane stress, could not be observed in the eel intestinal vesicles. The P _f dependence on the tonicity of the osmotic shock, described for kidney vesicles and related to the dissipation of pressure and stress at low tonicity shocks, was not seen with eel vesicles. These results indicate that the membranes from two volume transporter epithelia have different mechanisms of water permeation. Presumably the functional water channels observed in kidney vesicles are not present in eel intestine vesicles. The elastic modulus of the membrane was estimated by analysis of swelling kinetics of eel vesicles following hypotonic shock. The value obtained, 0.79 × 10⁻³ N cm⁻¹, compares favorably with the corresponding value, 0.87 × 10⁻³ N cm⁻¹, estimated from measurements at osmotic equilibrium. Received: 28 January 1999/Revised: 15 June 1999     

Interspecific and sexual differences in riverine distribution of tropical eels Anguilla spp.

A total of 261 individuals of the four tropical eel species, Anguilla celebesensis, Anguilla marmorata, Anguilla bicolor pacifica and Anguilla interioris, were collected from 12 locations around Sulawesi Island, Indonesia, to gain knowledge about the riverine distribution of tropical eels. Anguilla marmorata was predominant in the lower reaches of Poso River (94·4% of total eel catch in the sampling area), Poso Lake (93·3%), three small inlet rivers of Tomini Bay (100%) and Laa River (92·3%). Anguilla celebesensis occurred frequently in the inlet rivers of Poso Lake (63·5%). Anguilla bicolor pacifica and Anguilla interioris were rare (1.5 and 0.4%, respectively). Otolith Sr:Ca ratio electron‐probe micro analysis (EPMA) for individual migratory histories revealed that 15 A. celebesensis caught in Poso Lake and its inlet rivers were categorized into 14 river eels (Sr:Ca < 2·5) showing upstream migration seemingly at their elver stage and only one sea eel (Sr:Ca ≥ 6·0) that stayed in the marine habitat for the majority of its life after recruiting to Sulawesi Island before its late upstream migration. In A. marmorata, 19 examined eels from Poso Lake and its inlet rivers were all river eels, while 17 eels from the lower reaches of Poso River were two river eels, six sea eels and nine estuarine eels (2·5 ≤ Sr:Ca < 6·0) that mostly lived in the brackish water. The sex ratio of A. celebesensis was highly skewed towards a dominance of females (99%). In A. marmorata, females were predominant in Poso Lake (95·2%), its inlet rivers (94·7%) and Laa River (100%), while males were more frequent in the lower reaches of Poso River (76·5%) and small inlet rivers of Tomini Bay (94·1%). These results indicate that the riverine distribution pattern of tropical eels differs among species and between sexes.     

Novel tacrine-pyridinium hybrid reactivators of organophosphorus-inhibited acetylcholinesterase: Synthesis,molecular docking,and in vitro reactivation study

First-line medical treatment against nerve agents consists of co-administration of anticholinergic agents and oxime reactivators, which reactivate inhibited AChE. Pralidoxime, a commonly used oxime reactivator, is effective against some nerve agents but not against others; thus, new oxime reactivators are needed. Novel tacrine-pyridinium hybrid reactivators in which 4-pyridinealdoxime derivatives are connected to tacrine moieties by linear carbon chains of different lengths (C2–C7) were prepared (Scheme 1, 5a–f). Their binding affinities to electric eel AChE were tested because oximes can inhibit free AChE, and the highest AChE activity (95%, 92%, and 90%) was observed at 1?μM concentrations of the oximes (5a, 5b, and 5c, respectively). Based on their inhibitory affinities towards free AChE, 1?μM concentrations of the oxime derivatives (5) were used to examine reactivation of paraoxon-inhibited AChE. Reactivation ability increased as the carbon linker chains lengthened (n?=?2–5), and 5c and 5d showed remarkable reactivation ability (41%) compared to that of 2-PAM (16%) and HI-6 (4%) against paraoxon-inhibited electric eel AChE at 1?μM concentrations. Molecular docking simulation showed that the most stable binding free energy was observed in 5c at 73.79?kcal?mol^?1, and the binding mode of 5c is acceptable for the oxygen atom of oximate to attack the phosphorus atom of paraoxon and reactivate paraoxon-inhibited eel AChE model structure.     

Conclusive evidence for panmixia in the American eel

Eels are unique species in the biological world. The two North Atlantic eel species, the American eel (Anguilla rostrata) and the European eel (A. anguilla), occupy a broad range of habitats from the Caribbean to Greenland in the western Atlantic and from Morocco to Iceland in the eastern Atlantic, respectively. North Atlantic eels have a catadromous life cycle, spawning only in the Sargasso Sea and spending the majority of their lives in continental (fresh, brackish and coastal) waters. Despite such a wide distribution range, North Atlantic eels have been regarded as a textbook example of panmictic species. In contrast with the large amount of population genetic studies testing the panmixia hypothesis in the European eel, a relatively modest effort has been given to study the population structure of the American eel. In this issue of Molecular Ecology, Côté et al. ( 2013 ) present the most comprehensive American eel data set to date, which includes samples of different life stages obtained throughout all its distribution range in North America. Results show a total lack of genetic differentiation among samples and provide decisive evidence for panmixia in the American eel.     

Factors determining length distribution and abundance of the European eel, Anguilla anguilla, in the River Mondego (Portugal)

1. The distribution and abundance of the European eel, Anguilla anguilla, were investigated in the Mondego River, a strongly modified river in central Portugal. Nine freshwater sites, located below the first impassable obstacle to eel migration, were surveyed for 2 years. The study was conducted monthly during the first year and seasonally during the second year. Fish were caught by electric fishing and, physical and biotic variables potentially influencing eel length distribution and abundance were determined at each sampling session. 2. Canonical correspondence analysis (CCA) was used to explain the relationships between abiotic and biotic habitat variables, and eel length distribution. Spatial variation was strongly associated with distance from the sea, number of obstacles, river width and percentage of instream cover. Depth, river flow, water temperature and cannibalism had weaker effects on the longitudinal distribution, but contributed as explanatory variables for the model. The influence of spatial variables outweighed the importance of temporal variables as predictors in this model. 3. Length distribution changed in space from a dominance of small eels (<100 mm) closer to the sea to larger eels (≥250 mm) in the upper reaches of the river. The smallest length class (eels <100 mm) was strongly associated with wider stretches where instream cover, mainly composed of aquatic submerged macrophytes, was abundant (>75% area coverage). On the contrary, larger eels (≥250 mm) preferred deeper stretches with stronger river flow and less instream cover. 4. The effect of biotic interactions with conspecifics as well as with the non‐native red swamp crayfish Procambarus clarkii, in sites with poor instream cover, modified this general pattern of distribution leading to fewer eels <100 mm at some sites closer to the sea. Therefore, despite the ubiquity and plasticity shown by this species, there were clear ontogenetic variations in habitat use such that the first two canonical axes of a CCA accounted for 58.4% of the spatial variability in size structure.     

Broader head,stronger bite: In vivo bite forces in European eel Anguilla anguilla

This work examined three different phenotypes of the yellow‐eel stage of the European eel Anguilla anguilla, broad‐heads, narrow‐heads and eels with an intermediate head shape. The aim was to see whether broad‐headed A. anguilla, which generally consume harder, larger prey, such as crustaceans and fish, exerted greater bite force than the narrow‐headed variant, which mainly consume soft, small prey such as chironomid larvae. It was found that in 99 yellow A. anguilla, in vivo bite force of broad‐heads are higher compared with narrow‐heads and intermediates.     

Seasonal and size-related changes in the food of the short-finned eel,Anguilla australis in Lake Ellesmere,Canterbury, New Zealand

Synopsis An approximately monthly sampling programme in Lake Ellesmere, Canterbury, New Zealand, from January 1974 to April 1976 yielded 487 eels. The stomachs were fixed in 10% neutralised formalin and the contents examined. Preliminary analysis indicated that the mollusc Potamopyrgus antipodarum, the isopod Austridotea annectens, the mysid Tenagomysis chiltoni, the amphipod Paracalliope fluviatilis, the midge larva Chironomus zealandicus and the teleosts Retropinna retropinna, Galaxias maculatus and Gobiomorphus cotidianus together made up the bulk of the diet. The pre-ingested dry weight (i.e. the reconstructed weight) of the most important of these prey species was obtained by relating the length of a digestion resistant part to actual dry weight in field collected specimens. Regression equations for this relationship in each season enabled the reconstructed dry weight of each stomach item to be calculated. In some instances reconstructed weight was less than the actual digested dry weight of the prey specimen. In every case the larger value was used. This method is referred to as Combination Dry Weight (CDW) and is believed to be new. These data, used in conjunction with the energy content of the species concerned, enabled the caloric dietary contribution of each prey species to be determined. Comparison of relative contribution to eel diet between CDW and energy values calculated from CDW and bomb calorimetry revealed large differences. Marked variations in diet between ⩽40 cm, 40.1–50 cm, and>50.1 cm size classes were also shown. Eels ≤40 cm feed primarily on invertebrates and become progressively more piscivorous as they grow. Eels >50.1 cm are almost entirely piscivorous. Seasonal differences in diet also exist within each size class examined.