摘要:

Blubber samples from 18 harp seals taken near the Saguenay River in the Gulf of St. Lawrence were analysed for DDT metabolites, PCBs, and dieldrin. The concentration of total DDT and metabolitesranged from 3.1 to 22.6 ppm, PCBs (as Aroclor®1254) from 2 to 22 ppm, dieldrin from 0.1 to 0.3 ppm of blubber. Rank correlation of residue level and age indicated that significant portions of theand PCB variance could be assigned to increased residue levels with age. Within thegroup, DDE alone showed a strong proportional increase in concentration with age. Dieldrin concentration was not appreciably correlated with age. Among factors other than age, changes in blubber thickness did not account for any significant amount of the variance in blubber residue concentration. Examination of other published data suggested that parturition and/or lactation may cause reductions in blubber residue concentrations.

ISSN:0706-652X    

DOI:10.1139/f73-106

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The incidence of attack by the sea lamprey (Petromyzon marinus) was studied on freshwater teleosts of similar and different size. Splake (Salvelinus namaycush×Salvelinus fontinalis), carp (Cyprinus carpio), and white suckers (Catostomus commersoni) were attacked a significantly greater number of times than lake whitefish (Coregonus clupeaformis), burbot (Lota lota), shorthead redhorse suckers (Moxostoma macrolepidotum), and brown bullheads (Ictalurus nebulosus). Lampreys rarely preyed upon walleye (Stizostedion vitreum vitreum). Most attacks occurred between the head and caudal peduncle below the lateral line and particularly in the region behind the pectoral fins. Lampreys attacked the largest individuals of any species more frequently than the smaller representatives. The presence of lampreys on a fish did not further the incidence of attack on that fish. None of the species of fish appeared to avoid lamprey attacks, nor did they avoid fish on which lampreys were attached. Only rarely were fish observed to dislodge lampreys.

ISSN:0706-652X    

DOI:10.1139/f73-107

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The use of the scale method to determine age of mature white suckers should be avoided. Sections of pectoral fin rays can provide accurate age determinations for most populations once the position of the first annulus has been identified. The age of immature white suckers can be estimated by both methods. It is suggested that, for identification of the first fin ray annulus and facility in the determination of the age of immature white suckers, both pectoral fins and scales should be sampled in all age and growth studies of this species.White suckers (Catostomus commersoni) from populations examined in this study attained ages of up to 17 years although little or no growth occurred in the latter years. Considerable variation in size at sexual maturity was found throughout the range for this species and, thus, the validity of a subspecies designation for a dwarf white sucker (C.c.utawana) based primarily on size differences should be reexamined.

ISSN:0706-652X    

DOI:10.1139/f73-108

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Determination of respiration ofTubifex tubifex,Limnodrilus hoffmeisteri, andPeloscolex multisetosusin the laboratory provided evidence of interspecific interactions between two tubificid species. The same individuals in mixed species culture respire significantly less than in pure culture. The effector of the interaction in the one interaction betweenT.tubifexandL.hoffmeisteriis waterborne, smaller than 0.45 μ, and it is rendered ineffective by heating at 60 C for 20 min.

ISSN:0706-652X    

DOI:10.1139/f73-109

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

A method of estimating food consumption rates of fish in nature from laboratory growth data was evaluated using juvenile coho salmon (Oncorhynchus kisutch) in three similar experiments. One group of coho was held individually in aquariums where movement was restricted. Another group was maintained in an experimental stream where the coho displayed many of their typical behavior patterns. All fish were fed known rations and both groups had similar growth efficiencies over a wide range of rations. Coho feeding at intermediate rates had the highest gross efficiencies. Aggressive activity did not affect growth efficiency. Results suggested that laboratory food and growth data may provide reasonably accurate estimates of food consumption of coho salmon in nature.

ISSN:0706-652X    

DOI:10.1139/f73-110

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

This review considers questions concerning the growth and toxin production ofClostridium botulinumin cold-smoked salmon. In order to produce a product which would be safe as well as acceptable from the consumers’ point of view, consideration must be given to the worst abuses to which the product might be exposed. Present knowledge regarding the effects of salt, smoke, and other factors on the preservation of cold-smoked salmon is inconclusive. Strict control of the storage temperature is the only method of positively preventing toxin production or outgrowth of spores ofC.botulinum. In comparison with fish processed through a hot-smoke procedure, cold-smoked salmon appears to present a lesser hazard, but for unknown reasons.

ISSN:0706-652X    

DOI:10.1139/f73-111

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Rainbow trout (Salmo gairdneri) were held in cages in the South Saskatchewan River to assess mercury uptake following curtailment of mercury discharges to the river. There was a rapid uptake of mercury by the fish during the first warm summer period (1970) with much less uptake during the rest of the year. A second summer experiment (1971) produced no significantly different results suggesting that a long-term contamination exists within this river system. Analyses showed that the bulk of mercury present in the fish carcasses was present as methylmercury.

ISSN:0706-652X    

DOI:10.1139/f73-112

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Exposure of young Atlantic salmon (Salmo salar) to 1.0 ppm fenitrothion for 15–16 hr caused a 50% decrease in the number holding territories 6 days following treatment. Some severely affected fish also swam stiffly and ceased feeding, but these effects disappeared within 48 hr following return to clean water. Territories were not reclaimed for approximately 2–3 weeks. Exposure to 0.1 ppm fenitrothion for 15–16 hr caused a lesser (20%) reduction in numbers of fish holding territories.When mealworms (Tenebriosp.) injected with 2–5-μliters pure (100%) fenitrothion were force-fed to young salmon, 50% were regurgitated 8–12 hr afterwards. Almost all mealworms containing 10–20-μliter fenitrothion were regurgitated. The proportion of worms regurgitated remained constant during a week of daily force-feedings but, 24 hr after the third or fourth feeding, all fish except controls could be made to flex tetanically by rapping on the aquarium, and they made little attempt to escape a dipnet.

ISSN:0706-652X    

DOI:10.1139/f73-113

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Two long distance migrating fishes, the American eel (Anguilla rostrata) and the Atlantic salmon (Salmo salar), consistently showed conditioned cardiac responses to weak electric fields applied perpendicular but not parallel to their bodies. In fields with a power density of 0.11 × 10−3 pW/cm3, 63% of the eels tested were successfully conditioned, as were 56% of the salmon tested at 0.9 × 10−4 pW/cm3. At greater field intensities greater percentages of salmon and eels were successfully conditioned. However, at two lower intensities fewer salmon and no eels responded. These fields are of the magnitude that occur naturally in ocean currents. As geoelectric fields are perpendicular to the water motion that generates them, this sensitivity might allow a migrating fish to align itself upstream or downstream in an ocean current in the absence of fixed references. Results of magnetic conditioning experiments in eels were equivocal. Attempts to condition salmon to weak magnetic fields were unsuccessful.

ISSN:0706-652X    

DOI:10.1139/f73-114

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Three Nearctic species ofMonodiamesaare described:Monodiamesa depectinatasp.n. from male imagines, pupa, and fourth- and third-instar larvae;Monodiamesa tuberculatasp.n. from imagines, pupae, and fourth- and third-instar larvae; andMonodiamesa prolilobatasp.n. from male imagines. A larva possibly belonging toM.prolilobatais described. These are the first records and descriptions of imagines of Nearctic species of this genus.Keys are given for male imagines, pupae, and larvae of the Nearctic and Palaearctic species of the genus.Monodiamesa depectinataoccurs in the Laurentian Great Lakes area and in Lake Winnipeg, Man. It was taken from sandy substrates in the lower littoral and the sublittoral zones of oligotrophic to mesotrophic lakes.Monodiamesa tuberculataoccurs from the mainland of British Columbia through the prairie provinces and the Northwest Territories to the Laurentian Great Lakes. It was taken from the sublittoral and profundal zones of oligotrophic lakes and in some lakes is probably a glacial relict.Monodiamesa prolilobata, from west of the Rocky Mountains, probably covers the combined ecological niches of the two more easterly species.

ISSN:0706-652X    

DOI:10.1139/f73-115

出版商:NRC Research Press    

年代:1973

数据来源: NRC