A new species of Procamallanus (Nematoda: Camallanidae) from Pacific eels (Anguilla spp.)

A new species of parasitic nematode, Procamallanus (Procamallanus) pacificus n. sp., is described from the stomach of the Pacific shortfinned eel, Anguilla obscura (type host), and from the speckled longfin eel, Anguilla reinhardtii, from northern New Caledonia (Melanesia, South Pacific); from Anguilla sp. (cf. obscura) from the Fiji Islands (Melanesia, South Pacific); and from the giant mottled eel Anguilla marmorata from Futuna Island (Wallis and Futuna Islands, Polynesia). Although a total of 450 nematodes were collected, all specimens were females; this suggests either an extremely rare occurrence of males or parthenogenetic reproduction in this species. Procamallanus pacificus differs markedly from all congeners from fish hosts in possessing a greater number (4-9) of caudal mucrons in the female and by other morphological features. This parasite might become a serious pathogen of cultured eels in the region of the South Pacific. Batrachocamallanus Jackson and Tinsley, 1995 is considered a junior synonym of Procamallanus Baylis, 1923, to which 2 species are transferred as Procamallanus occidentalis (Jackson and Tinsley, 1995) n. comb. and Procamallanus siluranae (Jackson and Tinsley, 1995) n. comb. One third-stage larva of Procamallanus (Spirocamallanus) sp. was also recorded from Anguilla sp. (cf. obscura) from the Fiji Islands.     

Detection of infection and susceptibility of different Pacific salmon stocks (Oncorhynchus spp.) to the haemoflagellate Cryptobia salmositica

The haematocrit centrifugation technique, modified by keeping the haematocrit tubes cold (between 1 and 10 C), was sensitive for detecting light infections of Cryptobia salmositica (as few as 75 flagellates per ml of blood). In wet mount preparations, infections lighter than 7.5 X 10(3) flagellates per ml of blood could not be detected consistently. Different Pacific salmon stocks from British Columbia demonstrated differences in susceptibility to C. salmositica in experimental studies using laboratory reared juvenile fish. Oncorhynchus keta and Oncorhynchus tshawytscha from the Big Qualicum River stocks (Vancouver Island), and Oncorhynchus nerka from the Fulton River stock (Skeena River system), were all equally susceptible and suffered high mortalities at low exposures (100 flagellates in 0.1 ml physiological saline inoculated intraperitoneally per fish). Oncorhynchus nerka from the Weaver Creek stock (Fraser River system) was the most resistant with no mortalities even at exposures of 10(6) flagellates (in 0.1 ml physiological saline) per fish. Oncorhynchus kisutch seemed to be slightly less resistant than the Weaver Creek O. nerka, but fewer than 16% of the inoculated fish died. Oncorhynchus kisutch from the Big Qualicum River seemed to be slightly more resistant than O. kisutch from the Capilano River stock (a coastal river near Vancouver), with fewer mortalities and lighter infections when the experiments were terminated. Differences in susceptibility are believed to be associated with innate, genetically transmitted resistance.     

Chemosensory responses of juvenile Coho salmon, Oncorhynchus kisutch, Dolly Varden, Salvelinus malma, and sculpins (Cottus spp.) to eggs and other tissues from adult Pacific salmon

The carcasses of semelparous Pacific salmon (Oncorhynchus spp.) provide nutrients that enter aquatic ecosystems by various pathways, including direct consumption of tissue by fishes. Salmonids and other species frequently eat eggs and other tissues from dead salmon but the roles of vision and olfaction are unclear, as is the relative attraction to different tissues. Accordingly, we conducted a series of in situ experiments using minnow traps in two natural streams in Alaska to test the relative roles of chemosensory and visual cues in attraction of fishes to eggs from adult Pacific salmon, and then compared catch rates of traps baited with eggs, muscle, liver, and testis. Experiments indicated that chemical traces were necessary and sufficient to attract juvenile Dolly Varden (Salvelinus malma), coho salmon (Oncorhynchus kisutch), and sculpins (Cottus spp.) into traps. Combining both sites, 70 salmonids and 19 sculpins were trapped using visual and chemical cues, and 53 and 21, respectively, for traps with only chemical cues. Traps with only the sight of eggs caught no salmonids and only 5 sculpins, comparable to empty control traps. In addition, eggs were markedly more attractive than the other tissues, trapping 68?% of the salmonids and 69?% of the sculpins, compared to 14?% and 15?% for muscle tissue, 12?% and 11?% for liver, and 6?% and 5?% for the testis. Visual cues undoubtedly play a role in egg consumption in streams, but these experiments indicated a very important role of chemical traces in attracting fish to the vicinity of the eggs, and selective attraction of eggs over other salmon tissues.     

Timing games in the reproductive phenology of female pacific salmon (Oncorhynchus spp.)

We use a game-theoretic framework to investigate the reproductive phenology of female kokanee (Oncorhynchus nerka). As in the other semelparous species of Pacific salmon, females construct nests in gravel, spawn with males, bury their fertilized eggs, and defend their nest sites until they die several days later. Later-breeding females may reuse previous nest sites, and their digging behavior is thought to subject previously buried eggs to mortality. Using game-theoretic models, we show that females can reduce this risk by allocating resources to longevity (the period between arrival and death) as opposed to eggs. Waiting before territory settlement is also expected if it allows females to conserve energy and delay senescence. The models demonstrate how these costs and benefits interact to select for a seasonal decline in longevity, a well-known phenomenon in the salmonid literature, and a seasonal decline in wait duration. Both of these predictions were supported in a field study of kokanee. Female state of reproductive maturity was the most important proximate factor causing variation in longevity and wait duration. With more than 30% of territories being reused, dig-up is likely an important selective force in this population.     

Prevalence, intensity, and differential development of Pseudodelphis oligocotti (Nematoda: Dracunculoidea) in sympatric fish hosts of the northeastern Pacific coast

Counter to expectations of coevolved parasite-host relationships, parasites frequently infect hosts that never contribute to their reproduction, making the identification of a parasite's true host-specificity problematic. Pseudodelphis oligocotti (Nematoda: Dracunculoidea) infects several coastal Pacific fishes, but its course of development appears highly variable, suggesting that incidence does not reflect effective host range. To determine the host range of P. oligocotti and describe its relationship to various potential hosts, 24 fish species were examined from several British Columbia localities for prevalence, intensity, and extent and tissue location of parasite development. Pseudodelphis oligocotti infects 9 species of fishes from 5 orders, of which penpoint gunnel, Apodichthys flavidus, showed the highest prevalence and intensity, up to 80% and 19 (+/- 17.1 SD) worms per host, respectively. Although subadult and adult P. oligocotti occurred in all 9 fishes, larvigerous P. oligocotti only occurred in A. flavidus and rarely in the northern clingfish, Gobiesox maeandricus. Infective first-stage larvae were recovered from gill tissue of A. flavidus. Thus, at most only 2 of the 9 host species infected by P. oligocotti actually contribute to its transmission. The occurrence of P. oligocotti in diverse hosts may be accounted for by the parasite's indiscriminant mode of transmission via ingestion of free-living intermediate copepod hosts, where highly exposed or more suitable fishes (or both) are closely related by diet and microhabitat. This study demonstrates how parasite transmission and host ecology can greatly affect observed host range and ultimately its potential for expansion.     

Helminth parasites from North Pacific anadromous chinook salmon, Oncorhynchus tshawytscha, established in New Zealand

The following marine species of parasites are reported from the gastrointestinal tract of pre-spawning chinook salmon, Oncorhynchus tshawytscha, taken in the Rakaia River, New Zealand: the digeneans Derogenes varicus, Lecithocladium seriolellae, Parahemiurus sp., and Tubulovesicula angusticauda; and a tetraphyllidean metacestode, possibly of the genus Phyllobothrium. A small larval nematode tentatively assigned to the genus Contracaceum was found in the intestine and may be either of marine or freshwater origin. All are species acquired in the new environment of the salmon, descendants of stock introduced from California.     

Hellcotytencnus spp. (Nematoda: Tylenchida) from managed soils in New Zealand

Abstract

Helicotylenchus species collected from managed soils in New Zealand were identified. They were found at 159 sites. H. pseudorobustus was found at 82 of these sites, H. labiatus at 56, H. varicaudatus at 28, and H. canadensis at 4. Only 11 sites had more than one species present and most (7) of these sites had mixtures of H. pseudorobustus and H. labiatus. H. labiatus, reported only twice before, was the most common species found in cotula bowling greens. H. canadensis was restricted to sites south of 45°S. Measurements are given for 15 populations, and H. labiatus is illustrated. Characters separating the four species are given.     

Observations on the seasonal prevalence, pathology and transmission of Dracunculus insignis (Nematoda: Dracunculoidea) in the raccoon (Procyon lotor (L.) in Ontario.

Lesions due to Dracunculus insignis in the legs of raccoons (Procyon lotor) in southern Ontario occur seasonally as most larvigerous females emerge in the spring and early summer (April-June). The pathology of dracunculiasis in the raccoon is described and the transmission of the parasite in the wild is discussed with respect to seasonality and local agricultural practices. Crayfish, fishes and frogs (including tadpoles) were given infective third-stage larvae of D. insignis to test their suitability as paratenic hosts. Most of the larvae fed to adult Rana pipiens and R. clamitans were recovered from the somatic musculature. Larvae had increased in size and were highly infective to raccoons.     

Effect of salinity on hatching, survival and infectivity of Anguillicola crassus (Nematoda: Dracunculoidea) larvae

The effect of salinity on hatching, larval survival and infectivity of Anguillicola crassus was studied under experimental conditions using eggs obtained from naturally infected eels. Egg hatching rate, second-stage larval survival and larval infectivity were maximal in fresh water and declined with increase in salinity. Larvae survived up to 100 d in fresh water, 70 d in 50 % sea water and 40 d in 100% sea water. Infectivity experiments demonstrated that salinity influenced transmission success throughout the life cycle by decreasing total infectivity of the larval population in utero within female A. crassus and when larvae were free-living in the aquatic environment. Infectivity was age-dependent in relation to salinity. Larvae were infective to intermediate and paratenic hosts for up to 80 d in fresh water, 21 d in 50% sea water and up to 8 d in 100% sea water. The data confirm field observations that infection levels decrease with an increase in salinity. The study contributes to experimental verification of the colonization abilities of A. crassus and supports the hypothesis that A. crassus can be disseminated and transmitted in brackish water. The importance of regular monitoring and stringent hygiene practices in the transportation of eels is emphasized.     

Dioctophyme renale (Nematoda: Dioctophymatoidea) in the abdominal cavity of Rattus norvegicus in Japan

We collected 24 brown rats, Rattus norvegicus, in Kanagawa Prefecture in Japan and found one rat harboring a dioctophymatid nematode. A single male and a female worm were recovered from the abdominal cavity and were identified as Dioctophyme renale based on morphologic features and a BLAST DNA sequence analysis. We describe the morphological features of the adult worms and eggs from this extremely rare case of D. renale infection in a brown rat.     

In situ and laboratory studies on the behaviour and survival of Pacific salmon (genus Oncorhynchus)

Juvenile Pacific salmon display a marked surface water orientation during downstream migration, estuarine and nearshore coastal rearing phases. Many estuaries in British Columbia are vertically stratified with a shallow, well-defined halocline which can restrict the dispersion of wastes discharged into less saline surface waters and impose constraints upon aquatic organisms. In situ experiments in an estuary receiving a surface discharge of treated pulp mill wastes, revealed conditions which were lethal to underyearling salmon at, and below the halocline (4.0–6.5 m depth). Behavioural bioassays determined that juvenile chinook salmon were biased towards the water surface and avoided waters at depth. Dissolved oxygen was the variable which affected this distribution most significantly. Surface waters receiving effluent from another pulp mill were lethal to juvenile salmon within 350 m, and a significant vertical avoidance response occurred within 350–950 m of the outfalls. The behavioural response was significantly correlated with in situ temperature, pH and colour (effluent).As a complement to field experiments we developed a 4500 l water column simulator (WCS) to examine salmon behaviour in the laboratory. We investigated the surface water orientation behaviour of juvenile salmon in relation to variations in salinity and dissolved oxygen. Under simulated vertically stratified estuarine conditions, the fish moved freely between overlying fresh water and salt water. Induction of hypoxic conditions in fresh water elicited a downward distribution shift towards the halocline and oxygenated, but more saline, waters. Avoidance reactions (50% level) occurred consistently up to 7–8 mg · l^–1 dissolved oxygen. Salmon continued to examine the hypoxic freshwater zone despite sub-optimal conditions.     

Changes in the lipid class and proximate compositions of coho salmon (Oncorhynchus kisutch) smolts infected with the nematode parasite Philonema agubernaculum

Coho salmon (Oncorhynchus kisutch) smolts infected with the nematode Philonema agubernaculum had 36% lower mean lipid content (1.4%) than nonparasitized coho salmon (2.2%) harvested simultaneously from the same outmigration. Lengths, weights, and condition factors, as well as protein and moisture content, did not differ significantly between the two groups. Lipid class compositions differed significantly between the parasitized and nonparasitized fish. None of the nematode-infected fish contained detectable triacylglycerols (TAG) or monoacylglycerols (MAG). In contrast, mean TAG and MAG contents of the nonparasitized fish totaled 5.5% of the extracted lipid. Infected smolts had lower cholesterol contents than did uninfected coho (17% for infected, 33% for uninfected). Parasitized fish had significantly higher levels of free fatty acids (mean of 57% for parasitized vs. 35% for nonparasitized) as well as the phospholipids phosphatidylethanolamine (PE) and phosphatidylcholine (PC). However, the PC/PE ratios for infected and noninfected coho did not differ significantly (2.2 for infected vs. 2.0 for uninfected). These differences suggest that the parasitic nematodes are either harvesting storage energy directly from the coho or are placing additional energetic demands on the fish to cope with the infection.     

Acclimatization of salmon Oncorhynchus gorbuscha (Walbaum) in the European north: data from restriction analysis of mtDNA

Pink salmon spawners introduced into the White Sea basin (the Umba River) were compared to the spawners from the basin of the Sea of Okhotsk (the Ola River) using restriction analysis of two fragments of mitochondrial DNA (mtDNA). One of the fragments included genes ND5/ND6, the other, the cytochrome b gene and the control region. It was found that mtDNA variation and diversity at the earlier examined nuclear allozyme genes significantly decreased in the odd broodline of pink salmon 8 years after the introduction. The haplotype diversity in the even broodline was considerably lower than in the odd broodline exhibiting virtually no change two generations after the introduction. Based on the results obtained, a possible role of these changes in adaptation of White Sea pink salmon from the odd broodline to the new environment is discussed.     

Annual changes in the population size of the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) on high-seas Pacific Salmon (Oncorhynchus spp.), and relationship to host abundance

The population size of the salmon louse, Lepeophtheirus salmonis, was monitored annually in the summers of 1991–1997 by examining six species of Pacific salmon (Oncorhynchus spp.) caught by surface long-lines in oceanic offshore waters of the North Pacific Ocean and Bering Sea. The annual copepod population size on all salmonids caught was estimated by combining the calculated number of copepods carrying on each salmonid species. The copepod population fluctuated markedly from year to year, which resulted largely from marked annual changes in abundance of pink salmon (O. gorbuscha). Since pink salmon were most frequently and heavily infected and since their abundance changed every year, the copepod population was high in the years when this salmonid species was abundant, but low when it was rare. On the contrary, chum salmon (O. keta) did not show high prevalence and intensity of infection, but the annual abundance of this host species was consistently high, i.e. chum salmon carried many copepods every year. Copepods on other salmonid species (sockeye salmon O. nerka, coho salmon O. kisutch, chinook salmon O. tshawytscha, and steelhead trout O. mykiss) constantly formed a small percentage of the total copepod population. Both chum and pink salmon are the most important hosts in terms of their substantial contribution to support the copepod population, but the importance as hosts of each species is definitely different between the species. Chum salmon is a stable important host supporting the copepod population at a relatively high level every year, while the number of copepods on pink salmon annually exhibits marked fluctuations, and this salmonid species is regarded as an unstable important host.     

The major acidic glycolipids from the kidney of the Pacific salmon (Oncorhynchus keta): characterization of a novel ganglioside, fucosyl-N-acetylgalactosaminyl-GM1.

Two fractions of a major ganglioside from the kidney of the pacific salmon, Oncorhynchus keta, were eluted from a DEAE-Sephadex column in the monosialosyl fraction. The faster moving ganglioside (X1) on TLC was separated from the slower moving one (X2) by HPLC using a silica beads column. By methylation analysis, chemical and enzymatic degradation, reaction with monoclonal antibodies, LSIMS, and (1)H-NMR spectroscopy, X1 was determined to be a monosialosyl ganglioside belonging to the ganglio-series with a unique Fucalpha1-3GalNAc linkage at the nonreducing terminal: Fucalpha1-3GalNAcbeta1-3Galbeta1-3GalNAcbeta1-4[ NeuAcalpha2-3]Galbeta 1-4Glcbeta1-1Cer. Analysis of the lipophilic moiety indicated predominance of 24:1 fatty acid in combination with sphingenine. X2 was found to have a glycon structure identical to X1. The ceramide of X2 consisted predominantly of saturated fatty acids (18:0 and 16:0). The tissue concentrations of X1 and X2 in kidney were 3.7 and 2.8 nmol/g, respectively.     

Skrjabillanus cyprini n. sp. (Nematoda: Dracunculoidea) from the scales of common carp Cyprinus carpio (Pisces) from Hungary

A new species of the histozoic nematode, Skrjabillanus cyprini n. sp., is described from the subsquamal part of the scales of common carp Cyprinus carpio L. from Lake Balaton, Hungary. It differs from the other three congeneric species mainly in possessing an extremely small, oval-shaped buccal capsule with a large tooth at the bottom, in the shape of the cephalic end (somewhat bulbously inflated, truncated anteriorly), the extent of the oesophageal glands and body size (body length of male and female 1,800–3,000 µm and 3,200–4,100 µm, respectively). A key to the identification of Skrjabillanus spp. is provided.