摘要:

Thirty‐three collections ofGymnoscopelus nicholsiwere made between 1976 and 1981 in the South Atlantic using both krill and bottom trawls. In the Antarctic waters the main part of the stock consisted of adult fish 3–7 years old, characterized by a benthopelagic mode of life. Fish of year‐class I were observed only in the vicinity of South Georgia, South Sandwich Islands and the Scotia Sea; year‐class II individuals were absent from Antarctic samples. In the notal zone of the western South Atlantic, fish aged 1–5 years were found. The existence of only one population in the region is a possible explanation of these findings: this population is divided into a pelagic stock of juveniles and sub‐adults which occur in the offshore waters of the western South Atlantic and benthopelagic stocks of adults distributed over the slope regions off Argentina, South Georgia and Antarctic archipelagos.The computed values of K (von Bertalanffy growth) were 0.48, 0.41 and estimated total annual instantaneous mortality rates (Z) were 0.45, 0.67, and 0.70 for South Georgia, South Shetlands and notal zone of western South Atlantic stocks, r

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03213.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

We measured serum calcium concentrations in mature white suckers and bluegills collected from clear‐water Wisconsin lakes before spawning. The mean serum calcium concentration in female white suckers was greater in a circumneutral lake than in two naturally acidic lakes, whereas mean concentrations in fish from the two acidic lakes did not differ. Serum calcium concentrations in female bluegills from four acidic and four circumneutral lakes varied among lakes, but no relation was apparent between serum calcium level and either lake pH or waterborne calcium. In contrast, a strong negative correlation between mean serum calcium concentration and relative density of bluegill populations in the eight lakes was observed, suggesting that serum calcium levels in this species are affected by density‐dependent factors. Mean serum calcium concentrations were substantially lower in mature male bluegills than in females, which is the norm prior to spawning. We hypothesized that serum calcium levels in female white suckers are depressed by exposure to pH 6.0 or less in calcium‐poor waters. The utility of serum calcium concentrations, measured before spawning, as a measure of pH‐related stress on populations of white suckers and other synchronous spawners merits further study. However, this measure is probably not useful for evaluating acid stress on fish species such as the bluegill, which have asynchronous reproductive

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03214.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The river Nidelva, situated in central Norway, is regulated for production of electricity. Water discharge may vary from 150 to 30 m3s‐1 over a period of 10 min at the outlet of the power stations. The water level then sinks 50 cm during the next 30 min. The Nidelva produces both salmon and trout. Water fluctuations were found responsible for large losses of O+ salmon and trout. The recruitment of salmon was concluded as satisfactory, while recruitment of trout was reduced as a result of strandin

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03215.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Specimens ofHaptenchelys texts(9),Ilyophis arx(3),I. brunneus(36) (Synaphobranchidae),Nessorhamphus ingolfianus(5) (Derichthyidae),Nettastoma melanurum(9) andVenefica proboscidea(3) (Nettastomatidae) have been studied from collections in the eastern North Atlantic. An additional twoV. proboscideawere also included from eastern South Atlantic material. The samples were used to augment the incomplete descriptions of these scantily known species, in order to allow further clarification of their taxonomic status. Data from the three synaphobranchid species have been used to clarify the sub‐familial relationships and provide a preliminary family diagnosis. They have also been incorporated in an annotated key to the identification of the species found in the area. In an addition, all the specimens have provided supplementary information on the ecology of the various species, in aspects of distribution, both horizontal and vertical, diet and reproductio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03216.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Brown trout (Satmo truttaL) lymphocytes were shown to separate into two fractions on a Percoll discontinuous gradient, with 53% of the cells in the 1.07gl‐1fraction. The cells from the two fractions showed equal enzyme activity when stained for acid esterase and acid phosphatase. About 70% of the lymphocytes gave a positive enzyme reaction, which if the reaction is comparable with mammalian lymphocyte cytochemistry would indicate they were T‐lymphocytes. There appears to be increasing evidence among fish for the existence of T‐ and B‐lymphocytes, and cytochemical staining could prove a comparatively convenient method for their demons

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03217.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Non‐fed perch and perch fed a reduced ration were exposed to copper (0.15 of the 96‐h LC50) for 40 days. Starvation and growth rates were determined at 5‐day intervals to estimate the copper's effects on metabolism and food consumption. In general, copper increased starvation rates, reduced growth rates but did not affect food consumption. Weight reductions occurred in the first, but not in the second, 5‐day interval. There then followed an accelerated and linear weight reduction for 10–15 days, after which the rate of weight reduction was constant and at its highest level. Thus, perch did not acclimatize but a steady state of high metabolic cost was indicated over the last 20 days. The establishment and maintenance of this steady state was attributed to a detoxification mechanism. The increase in metabolic rate was, at steady state, estimated to increase the standard metabolic rate by at least 1.8 times. There was no apparent increase in specific dynamic action but increased activity due to an increase in competition for food was estimated to further increase the metabolic rate by

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03218.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Trawl surveys in an area of 237 km2to the east of Anglesey (Irish Sea) indicated a population of recruited plaice (c. 480000 fish) between 2 and 15 years old. Seasonal growth began in early April and annual growth in the dominant cohorts was analysed for males and females separately. Net annual production was estimated to be 0.17 g m‐2from a standing crop of 0.3 g m‐2;c. 50% of the production is removed by fishing. The annual consumption (2.5 g m‐2) ofAbraandPectinariawas converted with 6.8% efficiency by weight (8.0% in energy u

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03219.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The effects of an increase in group size on the location of a concealed food resource by stone‐loach were examined. Food was located more rapidly when group size was increased from one to five individuals. This was achieved by a reduction in the time taken to start searching for food, and by a reduction of travel time. We also found, at group sizes of two and five fish, consistent differences in individual foraging abilities, which were correlated with each fish's patch location performance when alon

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03220.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Acetazolamide‐sensitive esterase activity was elevated in branchial homogenates of control juvenile bluegill sunfish,Lepomis macrochirus, acclimated at 20° C but decreased rapidly within 9 h following an acute hypothermal shock to 8° C. After 2 weeks at 8° C, shocked‐fish enzyme activity was similar to control fish. At 20° C acclimation temperature, specific activity of bluegills was similar in swimbladder, liver, kidney, gill, spleen, and gonad homogenates and was significantly higher (α=0.05 level) in whole blood homogenates. The pH optima for enzymes extracted from fish acclimated at 20° and 8° C were 7.29 and 8.00, respectively. Polyacrylamide gel electrophoresis (PAGE) demonstrated two distinct forms of acetazolamide‐sensitive esterase activity present in both 20° and 8° C acclimated fish. Specific activity for homogenates from both 20° and 8° C acclimated fish differed significantly when assayed at 20° C, suggesting both qualitative and quantitative changes in acetazolamide‐sensitive esterase. It is postulated that relatively rapid alterations in esterase activity promote survival in bluegill following acute cold shock through the central role of enzymes in the regulation of plasma ion concentrations and a

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03221.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Comparison of the different populations of non‐anadromous Atlantic salmon in Europe has revealed some common traits. The non‐anadromous populations probably became isolated from the anadromous salmon populations during a period of rapid land‐upheaval after the last ice age, about 10 000 years ago. The oceanic temperature in the eastern part of the Atlantic was especially low in this period. This probably diminished the advantage gained from the anadromous habit. During this period the low temperatures in the rivers probably increased the frequency of females which matured without migrating seawards. A large number of individuals in the different populations seems to have been favourable for the formation and survival of such races. The occurrence of a lake in such a river system would probably ease the transition to non‐anadromous behaviour, because the salmon would not then be forced to adjust its entire life‐history when isolated (the salmon could spawn in the river in the usual manner and the smolts then migrate downstream into lakes). Larger lakes would also seem to infer problems for the navigation of the smolts towards the outlet. The only known exception is the river‐living land‐locked salmon population found in the River Namsen, Norway.The factors mentioned above have led to an increase in the probability of occurrence and thriving of mature females without a sea migration or to a decrease in the competitive advantage of anadromous behaviour. The above mentioned similarities can explain the seemingly casual distribution of the non‐anadromous populations of Atlantic s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03222.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY