摘要:

SUMMARY.The growth in length and weight (wet and dry) of 0+ perchPerca fluviatilisduring their first summer of life in Windermere, has been investigated. Two major stanzas, occurring during and after metamorphosis, characterize the growth of 0+ perch in Windermere. The change from one stanza to another takes place between six and eight weeks after hatching. The exponential rate of growth in length was 0.26 and 0.27 mm mm−1week−1for the first stanzas of 1975 and 1976, respectively, and decreased to about 0.08 and 0.07 mm mm−1week−1for the second stanzas of the same years. Similarly, the growth in both wet and dry weights decreased from the first to the second stanza. Growth of 0+ perch was found to be logistic, and could not be described by the von Bertalanffy growth curve. The relationship between weight and length was allometric and the power values for length were, for wet weight: 4.154 (in 1975) and 4.033 (in 1976) for the first stanza and 2.400 (in 1975) and 2.734 (in 1976) for the second stanza; for dry weight: 3.988 (1975) and 3.971 (1976) for the first stanza and 3.066 (1975) and 2.651 (1976) for the second stanza. Half of the total growth was completed in 47% (1975) and 40% (1976) of the total growth period to the end of the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01442.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.The rate of development and mortality of perchPerca fluviatiliswas studied at ten different constant temperatures. The rate of development was inversely related to the incubation temperature, whereas the rate of mortality was directly related to the incubation temperature. The sum of heat (ΣH, degree‐days) required for 10, 50 and 90% of the eggs to hatch was found to be constant, regardless of the incubation temperature, with mean values (with 95% confidence limits) of 91.4 (83.3–102.0) degree‐days above 4.6°C for 10% hatched, 97.0 (90.9–104.2) degree‐days above 4.9°C for 50% hatched and 101.0 (94.3–108.7) degree‐days above 5.0°C for 90% hatched. Mortality among the different embryological stages was highest for the pre‐hatching stage (i.e. when eye‐pigment has been formed) at all temperatures. High mortality among the early stages occurred at temperatures bel

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01443.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Opercular bones from 323 perch from the River Stour were used for age and back‐calculated growth determinations. Annuli were formed during May at the beginning of the growth period. Growth was minimal from October to April. Female perch grew faster than males, and the growth rates of both sexes were higher than those observed in most other European waters. Spawning occurred during late April and early May; male gonads began development in August and had attained their maximum weight in September, but the ovaries developed gradually from August until April. Immature perch had an annual cycle of condition with a maximum in June‐July and a minimum in December‐January. The condition of mature males and females was affected by the gonad cycle. The fecundity of Stour perch is expressed by the formula: log egg number = 2.40 log length (mm) ‐ 1.34.Approximately 25% of males were mature at age I and all were mature at age II, whereas most females did not spawn until age III. Ephemeroptera nymphs and minnow fry constituted the bulk of the diet of 0‐group perch; Ephemeroptera nymphs, minnow fry and Corixidae were the most numerous items in I group perch, whereas older perch contained Corixidae and a wider range of fish prey species, although minnows were the most numerous

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01444.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.An investigation into the ecology of benthic fauna in the eutrophic Lake McIlwaine (Rhodesia) was carried out in 1968–69. The profundal zone was only colonized in winter when the lake was isothermal and oxygen was present. The littoral zone was greatly affected by lake level fluctuation during the study period, and the population of lamellibranchs was destroyed by a drop in water level. While the water level was low, numbers of oligochaetes were high, but they declined as the water level rose. Chironomid larvae colonized the newly‐flooded land and their numbers increased considerably. The effects of eutrophication were less clear but it is suggested that the presence ofChironomusin the profundal in winter, and an increase inLimnodrilus hoffmeisteri, was linked with eutrophicat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01445.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Populations ofPotamogeton richardsoniiin Sparrow Lake, Ontario, vary greatly in leaf dimensions and internode length. Leaf length/breadth (L/B) ratio is increased by low irradiance, significantly at 4% daylight and, in a contrary fashion, by ontogenetic drift at high irradiances of shallow water.L/Bratio was not correlated with substrate. These findings suggest that this ratio is of doubtful value taxonomically or as an integrator, as specific leaf area is confirmed to be, of factors like photosynthetically active radiation (PAR). Longest internodes belong to plants from deep(1.8 m) water, and, in a summer‐grown high‐density population, internode length decreases logarithmically as depth lessens; both observations implicate PAR and ageing. Relative to undisturbed, shallow‐water shoots, young transplants in full daylight elongate almost twice as fast because of the production of more, and longer, internodes. Young shoots in 12% daylight lengthen even more rapidly than those in full daylight (and four times faster than undisturbed shoots) in the same period because of quicker elongation of the same number of internodes. At ambient summer temperatures, this rate of elongation is inversely related to PAR. Experimental and seasonal field data indicate that maximal internode extension occurs on young shoots in very low irradiances at temperatures of 9–15°C; in nature, effects of increasing water temperatures are depressed by increasing irradiances and ageing until minimal extension takes place in old shoots at mid‐ to late‐summer temperatures and in high irradiances. In tanks (40 m3) in full daylight, nutrients limit growth of plants on sand before they limit growth on clay (with marl intermediate) whereas, at 12% daylight, light limits growth on sand before soil nutrients do. The leaf area index on silty sand on an exposed shore was 0.4 at 0.5 m depth, in contrast to a cultured population where it was 4.0 in silty loam at the same depth. Thus, while it has not been possible to explain some variations in leaf morphology ofP. richardsoniiin environmental terms, the differential effects of ontogeny, PAR and temperature on shoot growth have been assessed, along with overall effects of light and nutrients on biomass and of shelter on lea

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01446.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.The effect of temperature on gut‐loading times, gut‐clearing times, and the calculated ingestion rates, egestion rates, and consumption indices of the deposit‐feeding burrowing mayfly,Hexagenia limbata, were investigated in laboratory experiments. Rates of movement of two natural sediments of differing colour through the digestive tract were monitored to quantify feeding intensity when ambient water temperatures approached 5, 10, 15, 20, and 25°C.At each temperature, gut‐loading times (GLT) and gut‐clearing times (GCT) increased as nymph length increased. Mean GLT and GCT values decreased as temperature increased from 5 to 20°C but were longer at 25°C than at 20°C. Relationships between GLT, GCT, and length of nymphs and temperature were best described by multiple regression equations. No diel variation in gutclearing times was observed. Low water temperatures resulted in lower ingestion and egestion rates and consumption indices. At most temperatures nymphs ingested over 100% of their dry body we

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01447.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Dense swarms were observed in a population ofDaphnia magna(Crustacea: Cladocera). The swarms appeared during a sexual period in which females were abundant but males were rare. Each swarm contained several males and large numbers of ‘imminently sexual’ females, a class of females that was rare except in the swarms. This implies that both sexes respond to attractant stimuli, and that the female response occurs only during a brief critical phase in the ovarian cy

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01448.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Benthic macroinvertebrate distribution, abundance, and composition were observed in a fluctuating (7.7 m) central Wisconsin, U.S.A., reservoir during 1973–74. Chironomidae and Oligochaeta represented 98% of the total fauna by number. The chironomid,Chironomus plumosus, and an oligochaete,Limnodrilus, each averaged 36% of the total benthic biomass. Annual mean numbers and biomass in areas exposed to air, exposed to ice cover, or remaining inundated were 3025/m2(1.8g/m2), 4311/m2(4.5g/m2), and 8558/m2(16.0 g/m2), respectively. A substantial portion of the benthic fauna was stranded and subsequently decreased rapidly in drying and frozen substrates exposed to air. Total benthic numbers and biomass were greatest immediately below the drawdown limit.Recolonization required 3 months (mid‐March to mid‐June, 1974) to attain pre‐drawdown values for numbers and biomass, and subsequently both were greater after reinundation than before the substrate was exposed. Recolonization of areas exposed to the air was greater in substrates containing large amounts of organic matter than in sandy areas containing little organic matter. Sorting and transportation of sediments redistributed organic materials from the regulated zone to below the drawdown limit, and macrophytes were eliminated from the regulated zone. When compared to other reservoirs and lakes, the density of benthos in the Big Eau Pleine Reservoir is neither high nor low. However, when compared with non‐fluctuating reservoirs the number of Ephemeroptera, Plecoptera, Trichoptera, Amphipoda, and Gastropod

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01449.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Interpretation of data collected from a spring‐fed stream suggests the existence of a phenomenon in running water that has not been previously described — salamander drift. Stream substrate and drift collections indicated that pre‐metamorphic salamanders (Eurycea bislineata) entered the water train and drifted during the months of April, May and June. Post‐metamorphic salamanders, and individuals about to undergo metamorphosis, did not appear in the strea

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01450.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY