摘要:

This work conducted during two seasons (May–October 1969, 1970) was designed to study the dynamic aspects of the settlement of benthic epifauna on hard substrata. The stations were distributed on a 200-km distance, the salinity gradient ranging from 15 to 27‰. Although over 60 species were identified on the plates, the analysis shows that only three of these are abundant:Polydora ciliata,Balanus balanoides, andBalanus crenatus. In general, the settlement period of the species is very short and most of the settling processes are concentrated in June, July, and August. The populations reached a peak of abundance during settlement and decreased regularly afterwards. This decrease is due mainly to intraspecific and interspecific competition for space, accumulation of sediment, and hydrodynamic factors in autumn. The marked physical seasonality of this subarctic environment, more than true biotic succession, is reflected in the development of the community: during the summer, the community is biologically accommodated, whereas in autumn and winter it is physically controlled.

ISSN:0706-652X    

DOI:10.1139/f73-149

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

A description is given of the life cycle ofSalmincola californiensis(Copepoda: Lernaeopodidae), studied by continuous observation of developing parasites and by intermittent examination of infected sockeye salmon (Oncorhynchus nerka). The cycle consists of six stages: copepodid (free-swimming), four chalimus stages (attached by second maxillae to frontal filament), and adult (attached by bulla). The copepodid settles on the fish and uncoils its frontal filament. Each successive chalimus stage reattaches the filament during moulting, but chalimus IV breaks off, searches for the site of final attachment, and excavates an implantation cavity for the bulla. The male cycle is similar but its chalimus IV is of shorter duration and soon moults into the male adult, actively searching for the female. Morphology of all stages is described in detail. Some comments are made on life cycles in Caligoida.

ISSN:0706-652X    

DOI:10.1139/f73-150

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Previous investigations have demonstrated that stimulation of gonadal recrudescence in the green sunfish (Lepomis cyanellus) depends on the concurrent presence of long photoperiods (15 hr) and elevated temperatures (> 15 C). The present investigation indicates that recrudescence can be stimulated in seasonally regressed ovaries and testes by injections of a crude extract of fish pituitary glands, and in testes by testosterone propionate, but only under elevated temperature. The low temperatures that block gonadal responses to long photoperiods also effectively prevent gonadal responses to administered hormones. These observations indicate that the responsiveness of the gonads of this species to stimulating hormones is markedly modified by temperature; however, the results do not obviate the possibility that secretion of gonadotropins by the brain–pituitary system may also be affected.

ISSN:0706-652X    

DOI:10.1139/f73-151

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

A monolayer culture of fibroblast-like cells was initiated from a trypsin digest of heart, liver, kidney, and spleen tissue of young Atlantic salmon (Salmo salar). This culture has been subcultured 81 times over a period of 21 months and appears to be an established cell line, which we have designated AS. Cells of the AS line multiply over a temperature range of 4–28 C with an optimum growth temperature of 20 C. Temperatures in excess of 29 C cause rapid cell death. The AS cells remain viable for periods up to 6 months at 4 C. An absolute plating efficiency of 30% has been determined for AS cells at 20 C. Analysis of the cell cycle of AS cells reveals a generation time (Gt) of 19.5 hr. The duration of the DNA synthetic period (S) is 10.5 hr, while the G1and G2periods are 1.1 and 7.1 hr, respectively. The duration of mitosis (M) has been calculated to be 0.9 hr with a mitotic index (M.I.) for the culture of 3.3%. Preliminary studies indicate a modal chromosome number of 54. The AS cell line is susceptible to infectious pancreatic necrosis (IPN) virus, infectious hematopoietic necrosis (IHN) virus and the myxovirus of bluegills.

ISSN:0706-652X    

DOI:10.1139/f73-152

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

The rate of change of heat contents in the lakes and the relative ability of each lake to transfer heat vertically to warm its hypolimnion was investigated. Rates of warming of hypolimnion water ranged from 0.06 C/month in Okanagan to 0.54 C/month in the north basin of Osoyoos. All lakes reached maximum static stability through the thermocline in late August except for Osoyoos (N), which reached its maximum somewhat earlier. Maximum heat content ranged from 18,100 cal/cm2in Wood Lake to 33,300 cal/cm2in Lake Okanagan. Maximum values of heat content were observed in late August in all lakes.There is a direct relation between the hypolimnetic warming rates and the maximum observed stability in the thermocline regions of all the lakes. However, the relatively low rate of Lake Wood indicates that there is an external cooling source such as groundwater influx. The late summer increase in volume of the epilimnion in Wood and the corresponding entrainment of nutrients from the hypolimnion to the epilimnion appear to control the amount of production observed at that time.

ISSN:0706-652X    

DOI:10.1139/f73-153

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Walleye (Stizostedion vitreum vitreum) and sauger (S.canadense) commonly yield four isozymes of malate dehydrogenase (MDH) in electropherograms of white muscle extracts from individual homozygous fish. The heat stability of each isozyme as well as reactivity with nicotinamide-adenine dinucleotide (NAD) and NAD analogues have been investigated by measuring the density of each isozyme directly on the electropherograms, after the usual specific staining procedure that links malate oxidation to tetrazolium dye reduction. At least two kinds of supernatant and one kind of mitochondrial MDH in individual fish of each species was demonstrated.Relative abundance of the various isozymes varies with the tissue of origin. In liver, only one heat stable isozyme is observed in both species, and it is likely constituted mainly of supernatant MDH. In heart tissue four isozymes are observed and the liver supernatant form also predominates. In white muscle the two kinds of supernatant MDH appear to be synthesized in comparable amounts and, including the mitochondrial MDH, four isozymes of nearly equivalent catalytic activity are produced. In walleye the three kinds of MDH homozygotes all showed similar enzymatic properties of their corresponding isozymes.In contrast to the polymorphic nature of walleye MDH isozymes the closely related sauger are monomorphic for MDH, and a number of analogous isozymes have identical electrophoretic mobility in the two species. More significantly, the major mitochondrial MDH isozymes have different mobility in each species. This fact is suggested as a taxonomic criterion to distinguish the two species. Some very rare fishes, evidently interspecific hybrids, produced three mitochondrial MDH isozymes. It was also possible to hybridize walleye and sauger MDH isozymes in vitro to produce phenotypes indistinguishable from presumed wild hybrid fishes.

ISSN:0706-652X    

DOI:10.1139/f73-154

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Two new "simple" fishery models based on delay-differential equations are introduced and compared to three currently used differential equation models. These new models can account for reproductive lag and allow oscillatory behavior of population biomass, but require only catch and effort data for their application. Equilibrium levels are calculated for both models and examples of various types of growth curves are given. Levels of fishing effort which maximize yield are calculated and found in one case to depend on the previous population and in the other to be constant.

ISSN:0706-652X    

DOI:10.1139/f73-155

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Infection incidence among 15 brood years of smolts in the period 1952–71 was estimated from smolt and underyearling samples, and among late run fish from the main part of Babine Lake ranged from 6 to 45% (average 26%). In early run fish from the North Arm–Nilkitkwa area it ranged from 5 to 46% (average 22%) in 10 years during 1958–71.Infection intensity changed substantially during 1967; but about one fish in eight, or 200,000 individuals in the early run, carried parasite loadsof fish weight. MatureE.salvelini(Schrank 1790) averaged 32 mg in weight and 34 mm in length during a period of high incidence and intensity of infection in 1967.Although no proof was found of direct mortality caused byE.salvelini, indirect effects such as inferior growth, poor swimming performance, or aberrant behavior due to large cestode loads may increase host susceptibility to death from other causes.Changes in relative abundance of the zooplankton intermediate host, and midsummer shifts in feeding preferences of young sockeye likely account for increasing infection incidence in June and July, and stable incidence thereafter.

ISSN:0706-652X    

DOI:10.1139/f73-156

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Thermally shocked juvenile rainbow trout and chinook salmon were selectively preyed upon by larger trout in the laboratory when exposure times to elevated temperatures exceeded a minimum duration. This duration was 10% (chinook) and 20% (rainbow) of the exposure duration that caused obvious loss of equilibrium (complete body inversion) of half a test population at that temperature. Longer exposures increased vulnerability to predation relative to controls almost exponentially. Shorter exposures made shocked fish less susceptible to predation. Shocked fish showed some recovery from heat effects when returned to the initial holding temperature foror 1 hr prior to predation. Susceptibility of rainbows to predation (relative to controls) appears to follow the time- and temperature-dependant response pattern previously shown by others for death and visible equilibrium loss. Selective predation began at exposures about 10% of the median death time in the range 26 to 30 C.

ISSN:0706-652X    

DOI:10.1139/f73-157

出版商:NRC Research Press    

年代:1973

数据来源: NRC

摘要:

Thermal requirements for brook trout reproduction were determined at a natural day-length cycle and five constant temperatures (10–21 C) and one treatment that followed the seasonal temperature regime of Lake Superior. The optimum range for growth (unrestricted rations) and relative condition factor was 10–19 C. Survival was 90% or greater and gonad growth and secondary sexual characteristics were well developed at all temperatures. The maximum temperature at which males became functionally mature and contained motile spermatozoa was 19 C. Ovulation and spawning occurred at 16 C and lower. Water temperature had little influence on time of spawning, but had a major influence on spawning activity and egg viability. The upper median effective temperature (ET50) for the number of viable eggs spawned per female was 11.7 C. The upper median tolerance limit (TL50) for normal hatch was 12.7 C; the optimum temperature was near 6 C. Major factors influencing the number of embryos surviving to hatch were spawning and incubation temperatures and age of the embryo when exposed to test temperatures. Thermal criteria that recognize seasonal changes in their thermal requirements are recommended for self-sustaining brook trout populations.

ISSN:0706-652X    

DOI:10.1139/f73-158

出版商:NRC Research Press    

年代:1973

数据来源: NRC