摘要:

Larvae of the nematodePhocanema decipiens(Ascaridida: Anisakidae), known as "codworm" in the vernacular, occur in the musculature of some cod and other marine fishes in both hemispheres, particularly in the temperate and polar climatic zones. The natural definitive hosts are Pinnipedia (seals, sea lions, walruses). For many years regarded incapable of surviving in man, recent reports from Japan indicate that in certain circumstances codworm larvae may temporarily invade the human gastric mucosa, producing clinical symptoms. Several nonclinical cases, in which the larval worms were expelled orally or in the feces of humans, have been reported from Canada (1), the USA (5), Greenland (1), and the U.K. (1). The source of human infections was raw, lightly marinated, or insufficiently cooked sea fish. The ability of codworm larvae to penetrate the stomach wall of other mammals has been demonstrated experimentally in rabbits, rats, dogs, and pigs. Natural infection of a dog in Hokkaido has been reported. For the human cases, information on age and sex of patients, specific source of infection, symptoms, and gross pathology are reviewed. The name applied to human infections and their diagnosis, treatment, prognosis, prevention, and public health implications are discussed. Cooking at 70 °C for 7 min or 60 °C for 10 min and freezing at −20 °C for 24 h are lethal to codworm larvae in fish flesh, thus providing reliable methods for preventing human infections. Some comparisons are made with larvalAnisakisinfections in man and future research needs, particularly in relation to the public health question, are discussed.

ISSN:0706-652X    

DOI:10.1139/f77-140

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

High concentrations of zinc and other heavy metals were found in lakes in the immediate vicinity of the Flin Flon smelters. In a study of 31 lakes, 7 had Zn levels above 100 μg/ℓ, 6 had levels between 50 and 100 μg/ℓ, and the remainder had concentrations < 50 μg/ℓ. The accuracy and precision of the heavy metal chemical analyses were evaluated using intercomparisons with other laboratories and a standard reference water. A linear relationship was demonstrated between log10concentration of Zn, Cu, and SO42−and log10distance from the smelter, suggesting atmospheric fallout as the main source of these substances in the lakes. Fishes were more tolerant of these high zinc concentrations than would be expected on the basis of the responses of fish and other aquatic organisms to similar concentrations of zinc in some laboratory toxicity tests.Key words: heavy metals, zinc, atmospheric fallout, fish toxicity, lake contamination, chemical analysis, Flin Flon, Canada

ISSN:0706-652X    

DOI:10.1139/f77-141

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Phytoplankton production and distribution were examined over a 2-yr period in relation to man-induced and natural factors that stress the system by mainly affecting the light regime in surface layer(s) of Howe Sound, British Columbia. Production rate and biomass values were greatest at the seaward boundary of the Sound where surface waters mix with the Strait of Georgia. Production decreases linearly in an up-inlet direction, reaching minimum values at the head of the Sound where the influence of the turbid Squamish River discharge is greatest. Annual production in the boundary waters of the Sound for 1973 and 1974 was 300 and 516 g C∙m−2, compared to an average of 118 and 163 for remaining stations. Strong light attenuation by the turbid Squamish River and flushing by the seaward moving surface layer were considered the most important factors controlling phytoplankton production and distribution in Howe Sound. Colored effluent from two pulp mills and turbid mine tailings and gravel washing water were minor perturbants to the system as a whole, but in affected bays and subregions of the Sound their effects on phytoplankton production were considerable. Annual production in Howe Sound was slightly higher than values for the Strait of Georgia and considerably greater than estimates from the North Pacific.Key words: phytoplankton, production, fjord–embayment, coastal marine, phytoplankton distribution, successi

ISSN:0706-652X    

DOI:10.1139/f77-142

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Phosphoais fractions in 15 samples of rain, rain plus dust, or snow were analyzed to shed light on the role of aeolian P in the nutrient budgets of lakes. Total Plevels varied (6.6 to 122.4 μg P/ℓ) but were generally high (mean = 47.0 μg P/ℓ; 76% of this was dissolved. Biologically available orthophosphate comprised an average of 38% of the total. Neither soluble reactive P nor small molecular weight P eluting with32P-PO4in gel filtration were consistently adequate estimates of orthophosphate concentrations.Key words: nutrient budgets, orthophosphate, phosphorus, bioassay,

ISSN:0706-652X    

DOI:10.1139/f77-143

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Number of young perch (Perca flavescens) consumed by walleye (Stizostedion vitreum vitreum) in Oneida Lake was determined from analysis of feeding chronology and digestion rates. Young perch were ingested between sunset and sunrise and digestion rates were estimated from the decrease in weight of perch in stomachs during the day. Walleye prédation began in late June and by October the number of young consumed ranged from 17,940 to 242,900 ∙ha−1in 1971–73. Concurrent studies indicated an additional 590 to 56,130 young were eaten by adult perch.Minimum population of young perch in June was calculated by adding to the number of young that survived to fall, the number consumed by walleye and adult perch. Populations reconstructed in this manner approximated independent estimates of the pelagic population in June. Mortality of young perch was apparently attributable to predation by percids and reconstructed populations accurately portrayed seasonal trends in abundance of young perch.Key words: predation, walleye, yellow perch, digestion, mortali

ISSN:0706-652X    

DOI:10.1139/f77-144

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Nine salmonid species and nine hatchery strains of chinook salmon (Oncorhynchus tshawytscha) were examined for susceptibility to infection byCeratomyxa shasta. All salmonid species tested were susceptible to infection by this myxosporidan, although no deaths occurred in the Atlantic salmon (Salmo salar). The level of resistance varied widely among the different species. A low prevalence of ceratomyxosis occurred in hatchery strains of chinook salmon from the Columbia River basin, while those chinook strains derived from outside this drainage system were highly susceptible to the parasite.Key words:Oncorhynchus tshawytscha, salmonidae, ceratomyxosis,Ceratomyxa shasta, resistance, susceptibility

ISSN:0706-652X    

DOI:10.1139/f77-145

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Residues of DDT group insecticides and of PCBs were measured in samples of maternal blubber, milk, and pup blubber from grey seals (Halichoerus grypus) from Sable Island, N.S. Mean ΣDDT and PCB levels in maternal blubber lipid were 14.0 and 14.5 μg/g, respectively. Concentrations of DDT and PCBs in milk lipid were approximately 60 and 30%, respectively, of those found in maternal blubber lipid, suggesting a partial barrier to passage of these residues through mammary tissue. Concentrations in pup blubber lipid were the same as, or slightly higher than, those in milk lipid.We estimated that a grey seal will lose about 30% of its total ΣDDT burden and about 15% of its PCB burden through lactation; this would be approximately balanced by its estimated annual intake of these residues from food. Thus, the observation that female seals show no increase in residue burdens with age (in contrast to males) is explained.Key words: organochlorine, DDT, DDE, PCB, seal, blubber, milk

ISSN:0706-652X    

DOI:10.1139/f77-146

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The life history of the exploited lake whitefish (Coregonus clupeaformis) population of Lesser Slave Lake, Alberta, is described. Mean age is high, having increased under continued exploitation during the last 30 yr. A method of estimating the population age structure is described. The apparent annual rate of survival of adult fish has fluctuated markedly, but on average seems to lie in the interval 0.40–0.50; the annual rate of natural survival is estimated to be 0.53. Juveniles survive better than adults. Rate of survival during the 1st yr of life was estimated to be about 0.0002. Maturity was late, the median age at first reproduction being 6–61/2 yr. The regressions of fecundity on age and length are described; length now contributes almost all the attributable variance to maturity and fecundity. The sex ratio fluctuates in time; this is caused by the fluctuations in age structure, since sex ratio varies with age. The relationship between sex ratio and age is used to calculate the relative rates of survival of male and female fish.These data are used to construct a life table and to compute population parameters. It is inferred that the ability of the population to respond to exploitation has been eroded during the last 30 yr. In some respects, the life history of the Lesser Slave Lake stock appears to be unusual.After about 30 yr of large-amplitude oscillation the whitefish population collapsed in 1965. This does not seem to have been caused by chronic overfishing. In the first place, the rate of fishing mortality is no more than moderate. Secondly, a multiple regression equation describing whitefish catch in 48 other Alberta lakes in which there has been no overall decline in catch successfully predicts the observed mean catch at Lesser Slave Lake. The oscillations in catch are claimed to reflect a limit cycle in the abundance of the whitefish, driven by a lagged relationship between a predator (the fishermen) and its prey (the whitefish). Whether or not this cycle was deterministically stable, such behavior will inevitably put the population in risk of extinction during troughs in the cycle. We suggest that current management policies may encourage the destabilization of whitefish populations, and we propose a remedy.Key words: population dynamics, population regulation, life history, exploitation, survival, fecundity,Coregonus clupeaformis

ISSN:0706-652X    

DOI:10.1139/f77-147

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Temporal patterns of change in growth, condition, and mean age of samples of lake whitefish (Coregonus clupeaformis) taken from Lesser Slave Lake, Alberta, during 1941–75 are described. Growth rate and condition have declined, while mean age has increased. Gillnet fisheries are highly selective of large, heavy, fast-growing individuals, and we suggest that culling of this sort will provoke an evolutionary response in the stock, which may be reflected in patterns of change in growth and age. This hypothesis and others are discussed, and the general importance of artificial selection in lake fisheries is briefly considered. The possible implications for fishery management are outlined.Key words: artificial selection, evolution, growth rate, gillnet,Coregonus clupeaformis.

ISSN:0706-652X    

DOI:10.1139/f77-148

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Principal component analysis is used to develop a technique for predicting the limnological characteristics of a lake from knowledge of its midsummer limnetic crustacean zooplankton community. Patterns of variation in zooplankton community structure are summarized in the principal components extracted, via the species covariance matrix, from the matrix of transformed proportionate numerical abundances of species in a sample of lakes. The relation between these patterns and the limnological characteristics of the lakes is determined from the first-order rank correlations of the limnological variables with the components. In relatively undisturbed lakes of northwestern Ontario, results indicate that lakes characterized byCyclops bicuspidatus thomasi,Diaptomus minutus, and others are large and clear, whereas those characterized byTropocyclops prasinus mexicanus,D.oregonensis, and others are smaller and of lower water clarity. These patterns are contrasted with those extracted from the same data using more subjective techniques. In the acid-stressed Killarney region, Ontario, lakes dominated byD.minutusare predicted to be acidic, small, and clear, whereas those dominated byDiaphanosoma leuchtenbergianum,Bosmina longirostris,Mesocyclops edax, and others will be less clear, larger, and with higher pH. In Haliburton lakes, Ontario, those withDiaptomus oregonensis,M.edax, andCeriodaphnia lacustrisare predicted to be small and productive, whereas those withD.minutus,D.sicilis,B.longirostris, andDaphnia dubiawill be larger and less productive. The usefulness of the technique and some modifications are discussed.Key words: zooplankton communities, principal component analysis, ELA lakes, Haliburton lakes, Killarney lakes

ISSN:0706-652X    

DOI:10.1139/f77-149

出版商:NRC Research Press    

年代:1977

数据来源: NRC