摘要:

SUMMARY.Embryonic durations and post embryonic growth rates ofCaridina niloticawere determined under laboratory conditions at constant temperatures near 18, 24 and 30°C. Embryonic durations and intermoult intervals were negative curvilinear functions of temperature. At a given temperature moulting frequency varied inversely with shrimp size and slight sexual differences were apparent. Moulting frequency of berried females was governed by the temperature‐specific embryonic durations.Growth rates were determined from changes in carapace length (CL) of individual shrimps (laboratory) or batches of shrimps (field enclosures) over 1 month and these data were used to calculate temperature‐specific life‐long growth curves for males and females. Growth in body mass was estimated indirectly from the carapace length‐mass relationship ofC. nilotica.On average, males grew marginally faster than females during the first 2 months of life, but growth of males larger thanCL= 4 mm was considerably depressed relative to that of females. Inflexions in growth rate, apparently related to the onset of sexual maturity, were apparent in both sexes.Under laboratory conditions, the growth rate of males increased with temperature, but temperature‐related differences were not as marked in females. Notwithstanding the more rapid moulting rate at 30°C the growth rate of females was slightly slower at 30 than at 24°C as a result of marginally but significantly smaller per moult growth increments observed at 30°C in animals up toCL= 5.5 mm. Possible reasons for this depressed growth are discussed.Growth rates of animals in field enclosures in Lake Sibaya over 1 month in winter (20 ± 3°C) were generally comparable to those estimated for the 18°C laboratory experiments. Growth rates in enclosures containing tripled standing stocks were almost identical to those containing the naturally occurring biomass of animals, suggesting a non‐limited environment at least during the time

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01205.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.The effects of temperature on development and growth are described for the common Cladocera and Copepoda in Tjeukemeer. Eight cladoceran species and five copepod species have been investigated:Daphnia hyalina, Daphnia cucullata, Bosmina coregoni, Bosmina longirostris, Chydorus sphaericus, Ceriodaphnia pulchella, Diaphanosoma brachyurum, Leptodora kindtii, Acanthocyclops robustus, Mesocydops leuckarti, Diacyclops bicuspidatus, Cyclops vicinus vicinusandEurytemora affinis. Growth is expressed as length increment per size class (cladocerans) or instar (copepods) per week and as the relationship between time and length. The curvilinear logarithmic equation: In D = In a + b (In T)2is fitted to the development times of eggs, combined naupliar instars and combined copepodite instars, as well as to the longevity of the adults. The results are compared with those found in the literature and differences are discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01206.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Denitrification processes in Grasmere were studied using several techniques. Sediments were analysed for nitrate reductase activity and the accumulation of nitrogenous gases in samples incubated in the laboratory. Changes in the concentrations of inorganic nitrogen species in the water column and the release of gas bubbles into gas traps suspended above the sediment were also measured. Sewage effluent entered the lake via the main inflow and faecal bacteria were used as tracers to map the path of the river (and effluent) across the lake. The main river flow was west of the island in the centre of the lake and across the smaller of the two main basins. A preliminary study indicated that this western basin was the site of most active denitrification and this was confirmed in the following year when a seasonal survey showed that deoxygenation, nitrate reduction and ammonium accumulation was more advanced at this site. In addition, this basin was the only area where consistent discharge of nitrogen and methane from the profundal zone was observed. The nitrate reductase assay demonstrated that the sediment was the major site of denitrification, and that activity in the water column was higher in the anoxic hypolimnion than in the euphotic zone. Gas evolution from incubated sediment samples was analysed by gas liquid chromatography (GLC) and indicated that maximum denitrifying activity occurred below the mud surface in oxidized sediments. There was reasonable agreement between the enzyme assay and the GLC technique but neither predicted events in the field satisfactorily. Viable, most probable number (MPN) counts of denitrifying bacteria had similar limitations. A bimodal seasonal pattern of nitrate reductase activity was observed at four sites during thermal stratification, but this could not be explained fully. The major site of denitrification was identified and it was calculated that the nitrogen gas discharged was equivalent to c. 54% of the nitrate removed from the water column.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01207.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Although morphological distinctions are well documented, many authors have regarded the freshwater bryozoanPlumatella emarginataas a variety ofP. repens.Differences between the two nominate species have been studied by the electrophoretic examination of genetic variation at enzyme loci. Genetic identity (Nei, 1972) was 0.286, a value well below that expected for conspecific allopatric populations. The results leave little doubt that specimens of the two species are from quite distinct and separate gene pools, with an unexpectedly high level of genetic differentiation. It is therefore concluded thatP. emarginatais a valid species and is not merely a variety ofP. repens.Morphological differences between the two species are also discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01208.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.A key is given for the identification of the larva ofTinodes maculicorniswhich is the only undescribed psychomyiid in the British Isles. The Irish distribution and habitat of the species are outlined.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01209.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Fish bearing celluloid bird rings on the anterior edge of the dorsal fin can be recognized individually in the field for several weeks. GraylingThymallus thymallus, over 20 cm long, in a fast‐flowing river retained recognisable rings for a mean of 47 days. Brown troutSalmo trutta, retained rings for comparable periods. Rings could be seen at distances up to 10 m, irrespective of the orientation of the fish to the observer. This marking technique compares favourably with other

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01210.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.Predictive equations were developed to estimate dry weight from body length measurements for forty‐three taxa of aquatic insects. The inter‐relationships between dry weight, body length and head capsule width of individuals grouped according to the eight major orders of aquatic insects were also examined. Regression analysis indicated that the relationship between biomass and body size was best expressed by a power equation, Y =aXb, rather than by linear or exponential equations. Changes in body length versus head capsule width were best expressed by linear equations, with three distinct relationships being observed. Body length estimated biomass better than head capsule width. Populations often species of insects collected from two different rivers generally did not differ significantly in their dry weight to body length relationsh

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01211.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARY.A method is described for isolating and sterilizing fronds ofLemnà gibba, L. minor, L. trisulca, L. polyrrhiza and Wolffia arrhiza, employing enrichment followed by sodium hypochlorite treatment. The method enables about 4% of the total number of treated fronds to be used as initiators of clonal cultures in which bacteria responding to organic enrichment and algae are excluded. Appropriate growth media, culture vessels and culture conditions are detailed

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01212.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

The status of Crangonyx pseudogracilis Bousfield in Britain

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1980.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY