摘要:

Forty years (1937–76) of data from Lake Michigan water intakes at Chicago, Illinois, were examined to explain reported differences in the apparent temperature optima of phytoplankton. The bimodal seasonal plankton distribution, typical at Chicago, still occurs. However, there has been a shift in seasonal periodicity with spring peaks occurring in March from 1957 to 1976 instead of May–June as previously reported for 1937–56. An optimum temperature of 10 °C for the plankton community was observed between 1936 and 1956, while for the last 20 yr an optimum temperature range from 0 to 4 °C was observed. This change in optimum temperature of the plankton community is related to a change in the abundance of the generaAsterionella,Fragilaria,Stephanodiscus, andTabellaria. AsterionellaandFragilariawere the dominant spring plankton with maximum standing crops observed around 10 °C prior to 1956.Stephanodiscusfirst increased significantly in 1957 and was the dominant spring plankter through 1976. More recently (1972–76), blue-green algae have increased in numbers. Differences in apparent temperature optima reported are real and are caused by the emergence of cold water species ofStephanodiscusas the dominant spring plankter from 1957 to 1976.Key words: plankton, temperature optima, Lake Michigan

ISSN:0706-652X    

DOI:10.1139/f79-168

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Grass carp (Ctenopharyngodon idella), bred in Arkansas and maintained in British Columbia under defined culture conditions on pelleted diets and on aquatic weeds, were examined to determine their commensal gastrointestinal bacterial flora. Using anaerobic incubation, the total bacterial numbers cultured ranged from 6 × 104to 4 × 108(average 4 × 106) per g of alimentary tract plus contents. Obligately anaerobic bacteria were isolated and identified as species ofActinomyces,Bacteroides,Eubacterium,Fusobacterium, andPeptostreptococcus. This is the first description of the presence of these strictly anaerobic organisms in the gastrointestinal tract of fish. Indeed, many of the anaerobes isolated did not conform to previously described species. Members of the GenusClostridiumwere also isolated by enrichment culture and appeared to be associated with a pond weed diet. A wide variety of facultative anaerobic bacteria were also isolated, withAeromonas hydrophilapredominating. The gastrointestinal tracts of goldfish (Carassius auratus) were also found to contain sizable numbers of obligate anaerobes, but the gastrointestinal tracts of hatchery-cultured rainbow trout (Salmo gairdneri) contained insignificant numbers.Key words: grass carp, anaerobic bacteria, gastrointestinal microflora,Aeromonas hydrophila, rainbow trout, goldfish

ISSN:0706-652X    

DOI:10.1139/f79-169

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

In the early 1970s Lake Huron fishermen converted their gill nets from multifilament to monofilament nylon web in the lake whitefish (Coregonus clupeaformis) fishery. Catch comparisons in the two gears showed that monofilament nets were 1.8 times more efficient (but varied seasonally), resulting in biased commercial catch statistics. The use of monofilament web has probably increased exploitation pressure on whitefish. Both gears selected whitefish of the same size despite stock differences in individual size and shape. Catches in both gears declined during the full moon phase, possibly due to increased net visibility.Key words: mono-multifilament gillnet efficiency, selectivity, lunar illuminance,Coregonus clupeaformis, Lake Huron

ISSN:0706-652X    

DOI:10.1139/f79-170

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Exposure of rainbow trout (Salmo gairdneri) to 5.7 × 10−10 M(5 × 10−5 mg/L) morpholine during smoking period did not influence the subsequent neural response to this substance, when tested immediately and 12 mo after smoking. No significant difference in the morpholine-induced responses was obtained between the exposed and unexposed fish. UsingN-ethylmaleimide, a sulfhydryl reagent, it was further confirmed that the morpholine-effect is caused by a mechanism not directly associated with the normal olfactory function. Perfusion of the olfactory organs with 1.0 × 10−1and 1.1 × 10−1 M(1%) morpholine for 10 min irreversibly inhibited the olfactory responsiveness to odorants. Sensitization of the olfactory bulbar electrical response is discussed in connection with homing of morpholine-imprinted salmonid fishes.Key words: olfaction, olfactory bulbar response, rainbow trout, salmon, imprinting, morpholine, homing, migration

ISSN:0706-652X    

DOI:10.1139/f79-171

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The crayfishOrconectes virilisis a major component of the benthos of three small lakes in northern Michigan. These lakes contained stocked brook trout (Salvelinus fontinalis) populations (age-0 and age-I) at densities of 188, 411, and 1398 fish/ha. Crayfish were preyed upon by brook trout, but only during their first year of life. Two-year production of age-0 crayfish was approximately 94 kg in each lake; brook trout consumed only about 1–2% in lakes with lower density offish. Even with greater trout density and accompanying higher rate of exploitation (40%), there was no impact on recruitment of young crayfish because compensatory mortality of crayfish occurred in lakes with less trout predation. However, stocking trout at higher densities decreased trout growth and condition. While 2-yr production was highest (59 kg/ha) in the lake stocked at the highest density and lowest (17 kg/ha) in one stocked at the lowest density, the former was achieved at the cost of a very slow growing trout population. Most of the crayfish production is not utilized as trout food but enters the non-predatory pool of detrital organic matter.Key words:Orconectes virilis, brook trout, predation, production growth, mortality

ISSN:0706-652X    

DOI:10.1139/f79-172

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A quantitative hypothesis is presented that current velocity and roughness at the sediment–water interface control the numbers, biomass, and growth of suspension-feeding macrobenthic animals. The controls are the effect of tidal currents on turbulent mass transfer of food to suspension-feeding animals and direct inhibition of growth and settlement by currents in excess of 12–30 cm/s. The rate of turbulent supply of ATP associated with seston is proposed as a practical way of determining growth potentials of suspension-feeding macrobenthos at current velocities less than 30 cm/s.Key words: sublittoral macrobenthos, tidal velocity, potential population growth, Bay of Fundy estuaries

ISSN:0706-652X    

DOI:10.1139/f79-173

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Variations in energy contents of liver and musculature of immature pollock (Pollachius virens) were analyzed by bomb calorimetry and then correlated to the liver index (liver weight as a percentage of body weight). For fish weighing between 400 and 1500 g, relationships between energy contents of liver and musculature and the liver index were described by mathematical functions. The mean energy content of other fish tissues, excluding liver, musculature, and gonads was constant. The total energy content of an immature pollock can thus be determined. The same relationships should be adaptable to other species that store their primary fat reserves in the liver.Key words:Pollachius virens, liver index, energy content

ISSN:0706-652X    

DOI:10.1139/f79-174

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Two forms of lake whitefish (Coregonus clupeaformisspecies complex sensu McPhail and Lindsey [1970]) were found in each of five lakes in Yukon Territory. They are characterized by differences in gill raker counts. Low gill raker fish are benthic feeders and are found almost exclusively near the bottom while high raker fish are largely plankton feeders, being found throughout the lake water column. High raker fish have longer and more closely spaced gill rakers than low raker fish. They also have shorter life spans and mature earlier than low raker fish. Lakes supporting these sympatric populations of lake whitefish have no cisco populations. The low gill raker member of these sympatric populations seems to be equivalent to most other Yukon lake whitefish whereas the high raker member appears to be the unusual member of each sympatric pair.Key words: whitefish, lake, feeding, morphology, growth, divergence, Yukon Territory, sympatric populations

ISSN:0706-652X    

DOI:10.1139/f79-175

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Seiche motions observed in San Juan Harbour with a bottom-mounted pressure gauge have been Fourier-analyzed and interpreted in terms of a theoretical model of oscillations in a rectangular basin with an exponential depth profile. Two of the observed periods (at 14.6 and 38.5 min) are identified with resonances of the basin; two other significant low frequency peaks (at 21 and 55 min) do not coincide with resonant periods of the basin and must be due to strong external forcing. Higher frequency fluctuations (20–160 s) are attributed to swell and to its subharmonic interactions with edge waves.Key words: water waves, seiches, mathematical model, Juan de Fuca Strait, British Columbia

ISSN:0706-652X    

DOI:10.1139/f79-176

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Observations made on the shelf-break front off Nova Scotia during winter on 2 successive yr show the concentration of chlorophyllain the euphotic zone to be correlated to the inclination of the subsurface front. The steepness of the front influences the depth to which phytoplankton are mixed which in turn controls the average amount of illumination received by a given cell. The two winter observations showed the subsurface front at each of two extremes: vertical with little phytoplankton biomass and almost horizontal with significant quantities of chlorophyll. Calculations were made as to the amount of production enchancement that could result from shallowing of the mixed layer by decreased frontal inclination. They show that during the winter under ideal conditions as few as 35 d of intermittent growth increase annual production in the frontal region by 25%.Key words: front, winter production, phytoplankton, shelf-break, chlorophylla, frontal oscillations, growth enhancement, stability, stratification

ISSN:0706-652X    

DOI:10.1139/f79-177

出版商:NRC Research Press    

年代:1979

数据来源: NRC