Calcium limitation in Daphnia magna

The role of ambient calcium concentrations on survival, moulting,growth and egg production was assessed in the cladoceran Daphniamagna. A threshold for survival was found in the range 0.1–0.5mg Ca l^–1, even when ionic strength of the medium waskept constant. Accumulated length and length specific dry weightwas retarded at low Ca (0.5–1.0 mg Ca l^–1) at foodconcentrations above incipient limiting level. For lower foodlevels, the effect of Ca on growth was less clear. The effectof low Ca on growth rate was most manifest during the firstdays after hatching, reflecting the higher Ca demands of theearly juveniles. Age-specific egg production was strongly reducedat Ca concentrations <10 mg Ca l^–1. This was partlyan indirect effect of reduced growth rates, but could also bean effect of higher energetic costs associated with Ca uptakein a Ca-poor medium. The high Ca demands in D.magna may notbe representative of other Daphnia species. Nevertheless, highspecific Ca content seems to be a common property of Daphniaspp. and Ca deficiency could be a major determinant of speciessuccess and community structure among crustacean zooplankton;it also puts constraints on carbon sequestration in the pelagicfood web of softwater lakes.     

Artemia habitats: Ion concentrations tolerated by one superspecies

The geographic distribution, history, and ionic composition of habitats of Artemia franciscana are reviewed with emphasis on habitats with extreme values for ionic concentrations or ionic ratios: a) high-chloride waters (sea water salterns and Zuni and Great Salt Lakes); b) high-sulfate lakes in Saskatchewan (Chaplin and Little Manitou) and on the Okanogan plateau of Washington (Penley Lake complex); and c) high-carbonate habitats in Nevada (Fallon), in California (Mono Lake) and in the Nebraska sandhills (Jesse and Antioch).First-instar nauplii from populations representative of each of these three habitat clusters were tested for tolerance of potassium (0–5 g K l^-1), magnesium (0–1.3 g Mg l^-1), and calcium (0\2–0.6 g Ca l^-1). Viabilities were recorded until survivors reached adulthood in pairs of simple defined synthetic culture media which differed in only one parameter. Eight populations showed four levels of tolerance of high potassium. Of four populations tested, all had high viability and fertility in media lacking potassium (above the level in the yeast diet). Artemia from sea water salterns or from Zuni, Chaplin, or Great Salt Lakes could not tolerate low levels of calcium (<20 mg l^-1). This accounts for their inability to tolerate hypersaline high-carbonate waters. Mono and Fallon nauplii had high viability and fertility in media with low levels of calcium (0–10 mg l^-1) but lacking magnesium. They could not survive for seven days, however, in low-calcium (< 10 mg l^-1) media that contained moderate amounts of magnesium (1.3 g l^-1), indicating that magnesium interferes with utilization of low levels of calcium.For each of the three cations, the range of concentrations encountered by each population in the habitat is narrower than the range affording high viability in laboratory media. As expected, the midpoints of the two ranges are sometimes similar. In many cases, however, the narrower range of ionic concentrations reported for lake water is at the end of the range affording high viability in the laboratory.     

Embryogenesis and regeneration of green plantlets from oat (Avena sativa L.) leaf-base segments: influence of nitrogen balance, sugar and auxin

The nitrogen composition and sugar and auxin concentrations of callus induction medium were optimized in order to improve the regeneration of green plants from two elite oat cultivars, Aslak and Veli. For both cultivars, the production of green plantlets was doubled by optimization. However, the results obtained also clearly demonstrated that cultivars of the same species may differ drastically in their requirements for essential media components. Veli clearly required higher total amounts of nitrogen (67.8 mM) than Aslak (44.9 mM) but less maltose and 2,4-dichlorophenoxyacetic acid (28 g l^-1 and 0.6 mg l^-1) than Aslak (38 g l^-1 and 2 mg l^-1). This result indicates that the optimal production of green plantlets through embryogenesis requires that media be optimized for each cultivar separately.     

Herbicide-tolerant Transgenic Pineapple (Ananas comosus) Produced by Microprojectile Bombardment

Transformed plants of the commercially important Thai pineapple(Ananas comosus‘Phuket’) were produced followingmicroprojectile-mediated delivery of the plasmid AHC25, carryingthe ß-glucuronidase (gus) reporter gene and the bialaphosresistance (bar) gene for herbicide tolerance, into leaves ofmicropropagated shoots. Transformed plants were regeneratedfrom bombarded leaf bases on Murashige and Skoog-based mediumcontaining 0.5 mg l^-12,4-dichlorophenoxyacetic acid, 2.0 mgl^-16-benzylamino purine and 0.5 mg l^-1phosphinothricin. Integrationand expression of thebar gene in regenerated plants was confirmedby Southern analysis and RT-PCR, respectively. Regenerated plantswere assessed in vitro and under glasshouse conditions for theirtolerance to the commercial herbicide Basta^TM, containing glufosinateammonium as the active component. Plants sprayed with Basta^TMcontainingconcentrations of glufosinate ammonium up to 1400 mg l^-1remainedhealthy and retained their pigmentation. The generation of herbicide-tolerantpineapple will facilitate more efficient weed control in thiswidely cultivated tropical crop. Copyright 2001 Annals of BotanyCompany bar gene, Biolistics, herbicide tolerance, pineapple, phosphinothricin (PPT)     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to aluminium, copper, lead or zinc in soft, acid water

Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo trutta L., were exposed to each of four trace metals (aluminium: 6000 nmol l^?1; copper: 80 nmol l^?1; lead: 50 nmol l^?1; zinc: 300 nmol l^?1) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 μmol l^?1. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 μmol l^?1, regardless of the presence of Cu, Pb or Zn; Al reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ‘swim-up’, surviving fry exposed to Al or Pb had lower whole body Ca, Na and K content, irrespective of pH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 μmol^?1, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 μmol l^?1. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 μmol l^?1, and by Cu at pH 5.6 and [Ca] 200 μmol l^?1. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 μmol I^?1. Zn enhanced calcification at pH 4.5 and [Ca] 200 μmol l^?1. In the absence of trace metals, low pH reduced body Ca, Na, K content and skeletal calcification at [Ca] 200 μmol l^?1. The uptake of Ca, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective of ambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by Al and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200–300° days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by Al and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft, acid water.     

Egg size and clutch size in two Daphnia species grown at different food levels

The effect of three different Scenedesmus food concentrations(0.04, 0.2 and 1 mg C l^–1) on maternal investment wasstudied in two cladoceran species of similar size, Daphnia pulicariaand D.hyalina. It was observed that as food concentration decreased(between 1 and 0.2 mg C l^–1), there was an increase insize, protein content, lipid content, carbon and mass of theegg, while, at the same time, the clutch size of the femalesbecame smaller. Such an increase in ‘per offspring investment’was reflected in an increase in body length, body carbon andbody mass of neonates as the food available for females decreased.However, in D.pulicaria this tendency was not maintained downat 0.04 mg C l^–1 in which there was a decrease of theegg characteristics mentioned above. Although, there are notavailable all the egg and neonate parameters of D.hyalina at0.04 mg C l^–1, the body length of the neonates was largerthan at 0.2 and 1 mg C l^–1. These results show that, asfood diminishes, these two cladoceran species are able to respondby decreasing clutch size, but increasing the size of egg, therebyincreasing the probability of neonate survival. This tendencyis probably maintained until the food concentration is too lowand the females have to reduce the energy allocated for reproduction.     

In Vitro Regeneration from Seedling Organs of Brassica oleracea var. italica Plenck cv. Green Comet I. Effect of Plant Growth Regulators

The calabrese cultivar Brassica oleracea var. italica cv. GreenComet was used in a study of the effects of exogenous hormoneson the growth and differentiation of seedling organs in vitro.Four types of explants were tested: hypocotyl segments, rootsegments, primary leaf discs and cotyledon discs. These explantswere incubated on media containing factorial combinations ofBAP x IBA, BAP x NAA, KN x IBA and KN x NAA (all at 0, 0.1,10 and 10.0mg l^–1). Hypocotyls were the most regenerativeexplants; shoot production was favoured by cytokinin: auxinratios greater than one and was decreased by IBA at 10 mg l^–1when callus was produced. Shoot formation from root explantsoccurred either in the absence of hormones or with low concentrations;no shoot was produced when any hormone was present at 10 mgl^–1. In contrast, shoot production from primary leaf diseswas favoured by high concentrations of both auxin and cytokininwith the combination of BAP and IBA the most effective. Shootproduction from cotyledon discs was sporadic with no consistentresponse on any auxin/cytokinin combination. After further experimentson the optimization of hormone concentration, the followingcombinations were chosen as allowing reliable regeneration:0.1 mg l^–1 BAP+0.1mg l^–1 IBA for hypocotyl segments,0.075 mg l^–1 KN +0.025 mg l^–1 IBA for root segments,and 5.0 mg l^–1 BAP+5.0 mg l^–1 IBA for leaf discs. Brassica oleracea var. italica, calabrese, tissue culture, seedling, auxin, cytokinin     

Effect of External Supply of Growth Substances on Axillary Proliferation and Development in Dioscorea bulbifera

Bulbil development in cultured nodes of D. bulbifera proceededin the absence of growth substances from the medium. When IAAwas incorporated into the medium at the concentrations of 5mg l^–1 and 10 mg l^–1 the cultured nodes producedlarger bulbils than in its absences. When the concentrationof IAA was increased to 15 mg l^–1, however, the culturednodes produced a callus instead of a properly organized bulbil.The dry weight of bulbils increased when kinetin was added tothe medium at the concentrations of 0.05, 0.5, and 2.5 mg l^–1.The greatest increase was with 0.5 mg l^–1 kinetin. Onincreasing the concentration of kinetin in the medium to 5.0mg l^–1 the tissue produced had smaller dry weight thanthose produced in the absence of growth substances. Additionof different combinations of IAA and kinetin to the basal mediumresulted in the production of normal bulbils, roots, and shootsin some instances (suitable combinations) and in the productionof callus and abnormal shoots in others (non suitable combinations).     

An efficient leaf-disc culture method for the regeneration via somatic embryogenesis and transformation of grape (Vitis vinifera L.)

By manipulating hormone levels, light intensities and temperature, we have developed an efficient leaf-disc method for the regeneration of plants via embryogenesis and for transformation in four genotypes of Vitis vinifera L. In MS basal medium supplemented with 1 mg l^-1 6-benzylaminopurine (BAP) and 0.1 mg l^-1 2,4-dichlorophenoxyacetic acid, leaf discs cultured for 2 weeks under dark conditions produced calli in over 80% of the cultures. These subsequently differentiated into pro-embryos and embryos only if kept under conditions of low light intensity (15 µE m^-2 s^-1) for 2 weeks before being transferred to conditions of high light intensity (60 µE m^-2 s^-1). If the calli were directly transferred to high light intensity, the differentiation into embryos was blocked and the calli turned pink. The somatic embryos germinated at a frequency of about 10% on NN basal medium and about 32% on NN medium supplemented with 1 mg l^-1BAP and 0.1 mg l^-1 indole-3-butyric acid. The embryos, however, germinated when pre-exposed to a low temperature of 4°C for 2 weeks. If they were transferred directly to room temperature under conditions of high light intensity (60 µE m^-2 s^-1), shoot buds were produced, whereas under conditions of low light intensity (15 µE m^-2 s^-1) secondary embryogenesis was induced. About 90-95% of the in vitro grown plantlets could be successfully transferred to soil. The above method was also applicable for developing transgenic embryos whose transgenic nature was monitored using #-glucuronidase as a reporter gene.     

The Interaction Between Silicon and Aluminium in Sorghum bicolor (L.) Moench: Growth Analysis and X-ray Microanalysis

Seeds of Sorghum bicolor (L.) Moench. were germinated on moistfilter paper for 6 d, before the seedlings were transferredto pots containing 500 µmol l^-1 Ca(NO₃)₂ for 2 d. Theseedlings were then treated with 0 or 100 µmol l^-1 Alin factorial combination with 0, 1400 or 2800 µmol l^-1Si for 8 d. The background solution used throughout was 500µmol l^-1 Ca(NO₃)₂. Aluminium treatment reduced root growthand caused a significant increase in shoot/root ratio. The presenceof silica in the solution significantly ameliorated the effectsof aluminium on root growth. Three treatment were selected for a microanalytical investigationof the basal region of the root: 2800 µmol l^-1 Si only;100 µmol l^-1 Al only; and a combination of the two. Inthe 2800 µmol l^-1 treatment silica was deposited in theendodermis, with the greatest accumulation being in the innertangential wall (ITW). When plants were treated with 100 µmoll^-1 Al only, aluminium concentration was highest in the outertangential wall (OTW) of the epidermis. The element was presentin the hypodermal walls and OTW of the endodermis and was notdetectable in the stele. With both 2800 µmol l^-1 Si and100 µmol l^-1 Al in the nutrient solution the two biomineralizationsites were the ITW of the endodermis, where silicon was themajor element deposited, and atypically in the OTW of the epidermiswhere both aluminium and silicon were present. The sequestrationof aluminium in the Al-Si deposit in the OTW of the epidermismay represent the mechanism that allows greater root growthin this treatment.Copyright 1993, 1999 Academic Press Sorghum bicolor (L.) Moench., aluminium, silicon, calcium, root, toxicity, biomineralization, X-ray microanalysis, freeze substitution     

Herbivorous nutrition of Cyclops vicinus: the effect of a pure algal diet on feeding, development, reproduction and life cycle

Nutritional requirements, functional response, development andreproduction of Cyclops vicinus were studied with exclusivelyalgal food. Phytoflagellates were found to be adequate foodresources for both juvenile development and egg production.Ingestion measurements were performed with Chlamydomonas reinhardii.The functional response data give evidence for low feeding efficiency,especially for the naupliar stages. A difference between naupliiand older instars was also found in their quantitative foodneeds. A higher threshold food concentration was observed fornaupliar development (0.4 mg C l^–1) than for copepoditedevelopment (0.2 mg C l^–1). The calculation of assimilationefficiencies suggests that the high food requirements are dueto low specific ingestion rates rather than poor assimilationefficiency. Development time decreased as algal density increasedand males developed more quickly than females at all food concentrations.Body size and carbon content increased with increasing foodconcentration. Continuous egg production was observed abovea food concentration of 0.5 mg C l^–1. The results haveimplications for the life cycle of C. vicinus. Summer diapauseis interpreted as a strategy to avoid starvation of the juvenilestages. The facultative herbivory of the adults might be anadvantage when competing against other more carnivorous cyclopoidcopepods. ¹Present address: Agricultural University of Wageningen, Departmentof Mathematics, Dreijenlaan 4, NL-6703 HA Wageningen, The Netherlands     

The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution: I. EFFECT OF CONCENTRATION

Experiments with simulated swards of perennial ryegrass (Loliumperenne L.) show the relationship between concentration in flowing nutrient solution, nitrate uptake,plant growth, and the chemical composition of roots and shoots.Rates of uptake exceeding 1 g N m^–2 d^–1 were maintainedat concentrations in solution down to 0•02 mg N l^–1. Short-term studies confirmed that at such lowconcentrations the plants were able to maintain rates of uptakeof about 85% of maximum. Between 0•2 and 200 mg N l^–1the concentration of in solution had little effect on rate of uptake or plant growth. With at 1000 and 2000 mg N l^–1 there was a marked reductionin weight of the shoots and, more particularly, in the lengthand tensile strength of the roots. There were several significanttrends in mineral composition of the plants (notably in S, Ca,Mg) which were apparently correlated with increasing concentrationof in solution.     

Calcium balance in Daphnia grown on diets differing in food quantity, phosphorus and calcium

1. The influences of dietary phosphorus (P) and food concentration on the calcium (Ca) balance in Daphnia magna were examined in this study at two different ambient Ca concentrations (0.5 and 10 mg Ca L^?1). Daphnia were grown by feeding the young adults differentially under contrasting dietary P conditions [molar C : P ratio = c. 900 and c. 90 as low P (LP) and high P (HP), respectively], ambient Ca concentrations [0.5 mg and 10 mg Ca L^?1 as low Ca (LCa) or high Ca (HCa), respectively] and food levels [0.15 or 1.5 mg C L^?1 as low food (LF) or high food (HF), respectively] for 5 days. 2. The specific Ca contents of daphniids (1.9–6.5% of dry weight^?1) increased with increasing Ca concentration, food level and dietary P content, although the food level did not affect the Ca content in the HPHCa treatment. A radioactive tracer method showed that the food level did not affect the influx of Ca from the water under LP conditions, but the Ca influx under HP conditions doubled with a HF level. A LP condition also led to a decrease in Ca influx with a HF level. 3. During the 3 days of efflux, generally only a small proportion of Ca (2.6–3.3%) was retained by the daphniids, but this retention increased (14–23%) under low ambient Ca concentrations and under P‐limitation. Excretion was the most important pathway for Ca loss (accounting for 50–60% of body Ca), followed by moulting (20–47%), but the relative contribution of these two pathways (excretion and moulting) did not vary among all the different treatments. The absolute loss of Ca through excretion and moulting, on the contrary, differed with different ambient Ca concentrations and dietary P conditions. A HF level led to an increase in the loss rates in most cases. 4. Our study strongly suggested that there is an interaction between an essential metal (Ca) and macronutrients (C and P) in freshwater crustaceans with HCa and P contents. The results imply that variation in environmental nutrient conditions may change the Ca budget in crustaceans and may affect the dynamics of Ca in the epilimnion of freshwaters.     

Clearance rates in the Arctic bivalves <Emphasis Type="Italic">Hiatella arctica</Emphasis> and <Emphasis Type="Italic">Mya </Emphasis>sp.

Filtration was studied in two Arctic clams, Hiatella arctica and Mya sp., collected in Young Sound, Northeast Greenland. Clearance rates were determined as a function of ambient temperature and algal cell concentration, using the clearance method and feeding with a unicellular flagellate. For both species, clearance rates increased with increasing temperature from <у up to 4-8°C. At higher temperatures, filtration ceased and the clams closed their valves. Clearance rates were also determined in temperate specimens of H. arctica collected on the west coast of Sweden. For these specimens, clearance rates increased with increasing temperature from 0 to 18-20°C. When weight-specific clearance rates were compared between the two populations and between species, there were no differences at 1°C. Clearance rates in Arctic H. arctica were maximal at algal cell concentrations corresponding to 2.5-8 µg chlorophyll a l^-1. Temperature compensation in Arctic bivalves is discussed and it is concluded that adaptations to constant low temperatures consist of a lower minimum temperature, for active filtration. Low clearance rates due to low temperatures did not seem to limit growth, under the prevailing conditions in Young Sound.     

Inducible pesticide tolerance in Daphnia pulex influenced by resource availability

Pesticides are a ubiquitous contaminant in aquatic ecosystems. Despite the relative sensitivity of aquatic species to pesticides, growing evidence suggests that populations can respond to pesticides by evolving higher baseline tolerance or inducing a higher tolerance via phenotypic plasticity. While both mechanisms can allow organisms to persist when faced with pesticides, resource allocation theory suggests that tolerance may be related to resource acquisition by the organism. Using Daphnia pulex, we investigated how algal resource availability influenced the baseline and inducible tolerance of D. pulex to a carbamate insecticide, carbaryl. Individuals reared in high resource environments had a higher baseline carbaryl tolerance compared to those reared in low resource environments. However, D. pulex from low resource treatments exposed to sublethal concentrations of carbaryl early in development induced increased tolerance to a lethal concentration of carbaryl later in life. Only individuals reared in the low resource environment induced carbaryl tolerance. Collectively, this highlights the importance of considering resource availability in our understanding of pesticide tolerance.     

Ultrastructure of Paraquat-treated Pine Cells (Pinus elliottii Engelm.) in Suspension Culture

The ultrastructure of liquid suspension cultures of Pinus elliottiiwas studied, noting characteristics of dividing and senescentcells. The cultures were treated with 0.01, 0.1, 1.0, and 10.0mg l^–1 paraquat, an herbicide which stimulates oleoresinsynthesis and resinosis in the xylem of treated pine trees.The ultrastructural effects of the toxin were studied at eachparaquat concentration over a period of 24 days. Destructiveeffects of paraquat on vacuolar and organelle membranes andcytoplasm are observable in one day in cells supplied with 10.0mg l^–1. At 1.0 mg l^–1 vacuolar membranes and cellorganelles are present at seven days, but the cultures continuallydecline until at 14 days they are dead. At concentrations of0.1 and 0.01 mg l^–1 the effects of the toxin on fine structurecannot be separated from normal cell senescence. At low concentrationsof paraquat the amyloplastids accumulate large amounts of starch.No accumulation of oleoresin was detected. The ultrastructuralobservations are correlated with physiological studies in suspensionculture and in living trees. Pinus elliottii Engelm., slash pine, suspension culture, oleoresin, amyloplastids, membrane permeability, autolysis, vacuoles, senescence, tannin, paraquat     

Effects of a Range of O2 Concentrations on Porosity of Barley Roots and on their Sugar and Protein Concentrations

Barley was grown at a range of oxygen concentrations (0.5–9mg l^–1), in nutrient solutions. Growth of both shootsand seminal roots was restricted by O₂ concentrations lowerthan 2–3 mg l^–1) but nodal root growth was not. Root porosities were increased even at those O₂ concentrationswhich did not restrict growth, and were inversely proportionalto the protein levels of the roots. Sugar concentrations increasedappreciably only at those O₂ concentrations which also restrictedgrowth. Hordeum vulgare L., barley, root porosity, sugar, protein, oxygen concentration     

The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes

The phytoplankton productivity and biomass of two large, freshwater Antarctic lakes (Vestfold Hills, eastern Antarctica) were investigated over a 12-month period. Crooked Lake was sampled at one site, while Lake Druzhby, a complex lake with two shallow and one deep basin, was subject to a more detailed investigation. Concentrations of chlorophyll a were usually below 1 µg l^-1, indicating ultra-oligotrophic conditions. Despite periodic low nutrient levels, low temperatures (range 0.4-2.8°C) and periodic poor light climate, some degree of photosynthesis was measurable throughout the year, including the dark winter phase. Snow cover had a pronounced impact on the light climate of the water column and inhibited photosynthesis. Mean rates of carbon fixation in the 0- to 15-m water column varied between 0 and 38.47 µg C l^-1 day^-1 in Crooked Lake and 0.24 and 37.68 µg C l^-1 day^-1 in Lake Druzhby. There were significant differences in the seasonal patterns of primary production between the basins of Lake Druzhby. The shallow basins had highest productivity in August, whereas the deep basin had highest rates in summer. Chlorophyll specific rates of photosynthesis or assimilation numbers [µg C (chl. a)^-1 h^-1] varied between 0.05 and 44.9, and photosynthetic efficiency [µg C (chl. a)^-1 h^-1 µmol m^-2 s^-1] between 0.02 and 5.19. The data suggest that the phytoplankton of these lakes is adapted to low irradiance levels, low temperatures and nutrient limitation.     

Variability and interactions of phytoplankton and bacterioplankton in Varano lagoon (Adriatic Sea)

Bacterial abundance was investigated in Varano lagoon for a12 month period. The concentrations were found to be quite high(1.8 ± 2.2x10⁹cells l^-1) as well as being coupled tophytoplankton biomass and phosphorus content. However, an inverserelationship with nitrogen was detected.     

Calcium‐dependent behavioural responses to acute copper exposure in Oncorhynchus mykiss

Using rainbow trout Oncorhynchus mykiss, the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre‐exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu‐contaminated water (ranging from 0 to 454 µg Cu l^?1) and uncontaminated water in a choice tank, O. mykiss acclimated and tested at low Ca concentration (3 mg Ca l^?1) avoided the 10 µg Cu l^?1 only. By contrast, O. mykiss acclimated and tested at high Ca concentration (158 mg Ca l^?1) avoided all the Cu concentrations ≥37 µg l^?1. The Cu avoidance was connected with increased spontaneous swimming speed in the Cu‐contaminated water. When subjected to inescapable Cu exposure (35 µg Cu l^?1), O. mykiss acclimated and tested at low Ca concentration reduced their spontaneous swimming speed, whereas no response was observed in O. mykiss acclimated and tested at high Ca concentration. Collectively, the data support the conclusion that in O. mykiss the behavioural responses to acute Cu exposure are Ca‐dependent.