Dissolved oxygen and fish distribution in a Florida spring

This study examined the distribution and relative abundance of fishes along a dissolved oxygen gradient in Singing Springs, Florida. Over the 1-year study, dissolved oxygen concentration in the spring exhibited a strong gradient ranging from an average of 0.20 mg l^–2AM¹ at the boil to 1.81 mg l^–2AM¹ 110 meters downstream. Seasonal variation in dissolved oxygen was very low relative to the spatial variation along the spring gradient. Fish community composition was evaluated monthly at the boil of the spring, 45 m downstream just after the confluence of the spring and the main river, and 110 m downstream. The fish community in the spring was characterized by species generally considered to be tolerant of low oxygen. Gambusia holbrooki was the most abundant species at all sites comprising an average of 88.1% of the fish captured at the boil, 63.2% of the fish captured at 45 m, and 74.8% of the fish captured at 110 m downstream. The diversity of fishes (G. holbrooki, Heterandria formosa, Notropis harperi, Lucania goodei, and Poecilia latipinna) increased with distance from the boil. Although there were some seasonal differences in patterns of diversity and community structure, the inter-site differences were much more apparent throughout the study. It is likely that the pattern of variation in dissolved oxygen interacts with the respiratory abilities of the fishes to affect the distribution pattern and community composition along the gradient.     

Phytoplankton growth and krill grazing during spring in the Bransfield Strait,Antarctica — Implications from sediment trap collections

Summary Phytoplankton primary production, biomass, species composition and sedimentation of organic matter (using a moored and a free drifting sediment trap) were measured in eastern Bransfield Strait during spring 1983. Biomass and primary production increased from low levels in late November (1 mgChla m^-3 and 400 mgC m^-2 d^-1) to bloom levels by the end of December (5 mgChla m^-3 and 1000 mgC m^-2 d^-1). The moored trap was deployed at 323 m depth for 22.5 days, and collected 2968 mgC and 67.6 mg chlorophyll a and derivatives per m² (132 and 3.0 mg m^-2 d^-1), of which 90% was in the form of krill faeces. These figures are regarded as egestion of krill, and using ingestion: egestion ratios from the literature, grazing loss of phytoplankton by krill was estimated at 45% of the primary production during a period of 3 weeks. Large-scale surveys of phytoplankton standing stock indicate that the build-up of blooms during spring is apparently not controlled by krill grazing. It is therefore suggested that the intense grazing that must have occurred over the trap during the period of deployment was only of local importance.     

Interactions of feeding rates on growth,food conversion and body composition of the freshwater catfish Mystus vittatus (Bloch)

Food intake, growth, conversion efficiency and body composition of the non-air breathing catfish Mystus vittatus (Bloch) were studied in relation to different feeding levels. Fish weighing 817.9 ± 104.00 mg was found to consume a maximum of 156.0 mg live Tubifex worm/g day^-1. Geometrically derived feeding rates of 6.75, 23.00 and 26.00 mg dry food/g live fish day^-1 represent the maintenance, optimum and maximum levels respectively. The SDA increased from 6.75 mg/g day^-1 at maintenance to 13.50 mg/g day^-1 at maximum feeding rate. Starvation brougt about increase in body water content, while there was concomitant decrease in fat and crude protein.     

Role of aquatic vegetation coverage on hypoxia and sunfish abundance in bays of a eutrophic reservoir

We studied the relation between aquatic vegetation coverage, summer dissolved oxygen and density of sunfishes (Lepomis spp.) in 10 shallow bays of a eutrophic reservoir. The bays ranged 5.2–15.7 ha in area, 0.6–1.3 m mean depth and 6–91% vegetation area coverage. Over the 10 bays mean dissolved oxygen concentration ranged 5.8–9.0 mg l^-1 in open water at least 20 m away from the vegetation, 0.8–8.1 mg l^-1 at the vegetation-water edge and 0.5–7.7 mg l^-1 in dense vegetation. Dissolved oxygen concentrations were inversely related to vegetation coverage. In open water, dissolved oxygen levels were consistently higher than 8 mg l^-1 when vegetation coverage was <20% of the bay and decreased to about 6 mg l^-1 at coverages near 80%. At the vegetation-water edge and within dense vegetation, dissolved oxygen levels dropped rapidly as vegetation coverage increased to 20% of the bay; when vegetation reached about 50% coverage, dissolved oxygen remained near 1.5 mg l^-1at the vegetation-water edge, but oxygen dropped below 1 mg l^-1in dense vegetation. Scarce vegetation harbored high Lepomis relative abundance (fish per m² of vegetation) whereas extensive vegetation harbored low relative abundance, both contributing little to absolute abundance (total fish in all vegetation); however, intermediate coverage offered a combination of mid-level fish relative abundance that together with mid-level plant coverage translated into high absolute fish abundance. We suggest this response is related to hypoxia, and where aquatic vegetation is extensive, the effect of vegetation on hypoxia and water quality in general may influence fish populations in a way similar to that often attributed to reduced foraging efficiency and increased competitive interactions.     

The effects of dissolved oxygen and aquatic surface respiration on the critical thermal maxima of three intermittent-stream fishes

Synopsis Critical thermal maxima (CTM) were determined for three species of fish in hypoxic (1.2 mg l^-1), normoxic (7 mg l^-1) and hyperoxic (12 mg l^-1) oxygen tensions. All fish were acclimated to 30°C under a regulated photoperiod of 12:12. During each CTM determination, one-half of the test fish were allowed free access to the surface (to permit aquatic surface respiration) while the remaining one-half were denied access to the surface. Under hypoxic conditions, CTMs of Fundulus notatus, Notropis lutrensis and Pimephales vigilax given access to the surface were significantly higher than those of conspecifics without access to the surface. With access to the surface, all species had significantly lower CTMs under hypoxic conditions than under normoxic and hyperoxic conditions. CTMs measured under normoxic and hyperoxic conditions were not different for any of the test species. Under all comparable oxygen tensions with surface access, F. notatus had the highest CTM, N. lutrensis intermediate and P. vigilax had the lowest CTM. The critical oxygen concentration for N. lutrensis during CTM determinations occurred between 1.2 and 2 mg l^-1.     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Contaminants in tilapia (<Emphasis Type="Italic">Oreochromis mossambicus</Emphasis>) from the Salton Sea,California, in relation to human health,piscivorous birds and fish meal production

A summary of all existing information collected since 1980 on contaminants in tilapia from the Salton Sea is presented and risks to humans and fish-eating birds assessed. Of the 17 trace elements, 42 organic pesticides and 48 polychlorinated biphenyls (PCBs) analyzed in tilapia whole body and fillet samples, only selenium (Se), arsenic (As) and possibly dichlorodiphenyltrichloroethane (DDE) were found at levels high enough to be of concern for fish, birds or humans. Average current concentration of arsenic (As) was 0.7 μg g⁻¹ wet weight (ww) in whole body samples and 1.2 μg g⁻¹ ww in fillet samples, or 2.8 and 5.7 μg g⁻¹ dry weight (dw), respectively. Inorganic As averaged 0.006 μg g⁻¹ ww (0.03 μg g⁻¹ dw) in fillet samples, which represented 0.3% of total As. By U.S. Environmental Protection Agency (U.S.EPA) guidelines, As levels in tilapia pose no threat of non-cancerous adverse health effects in children and adults. As is a known human carcinogen, however, and U.S.EPA cancer risk assessment procedures indicate that a weekly consumption of 540 g (19 oz) or more for 70 years would increase the upper bound cancer risk by 1 in 100,000 consumers exposed. Average current Se concentration was 2.2 μg g⁻¹ ww in tilapia whole body samples and 1.9 μg g⁻¹ ww in fillet (8.3 and 9 μg g⁻¹ dw, respectively). Consumption of Se-contaminated tilapia was found to present no unacceptable risk for adverse health effects for adults consuming up to 1000 g (35 oz) of fillet per week even when additional intakes of Se from other food items were taken into account. Similarly, children weighing 30 kg or more could safely eat up to 430 g (15 oz) of tilapia fillet on a weekly basis. A health advisory issued by the State of California in 1986 recommended, on the basis of Se levels, that consumption of any fish from the Salton Sea be limited to 114 g (4 oz) every 2 weeks, but the rationale and calculations on which that advisory was based are unavailable. We suggest that the existing health advisory for Salton Sea tilapia be revised by the state in light of this new information and updated risk parameters for As and Se. Dichlorodiphenyltrichloroethane (DDE) was detected in all samples of tilapia, with current levels averaging 0.085 μg g⁻¹ in whole tilapia and 0.032 μg g⁻¹ in fillet ww. Compared to screening values proposed by the U.S. EPA, these concentrations are unlikely to cause non-cancerous health effects in anglers, but one might exceed a 1 × 10⁻⁵ increase in cancer risk by consuming more than 4 meals of tilapia per week. Similarly, polychlorinated biphenyls (PCBs) were detected in tilapia fillets at levels that may increase the cancer risk for those anglers also eating more than 4 meals of tilapia per week. These determinations are based, however, on DDE concentrations reported from a small sample size (n = 4), and on screening values recommended by U.S.EPA. The paucity of DDE and total DDT analyses carried out in recent times on the edible portion of Salton Sea tilapia warrants additional analyses in order to evaluate the need for issuance of a fish consumption advisory with regards to long term exposure to total DDT via consumption of Salton Sea fish. With regards to the potential impact on fish and piscivorous birds, we cannot conclude whether concentrations of As in tilapia could pose a threat to the fish and the birds feeding on them. Se concentrations, however, may be elevated enough to negatively affect fish health, and reproduction and immune systems of piscivorous birds, but definitive studies are lacking. Total DDT and PCB concentrations in whole tilapia are not elevated enough to have adverse effects on fish and piscivorous birds. Fish harvesting for fish meal production has been proposed for the Salton Sea. Based on whole fish dry weight values of 61% protein and 21% ash, and the determined contaminant levels, tilapia could yield a meal of reasonable quality for use in formulating poultry, livestock and aquaculture feeds. Guest Editor: John M. Melack Saline Waters and their Biota     

Behavioral responses of red hake,Urophycis chuss,to decreasing concentrations of dissolved oxygen

Synopsis Laboratory experiments were conducted to examine changes in behavior of red hake,Urophycis chuss, under decreasing concentrations of dissolved oxygen (DO). Since the ecological requirements of this species change with age, responses were measured for three different groups: (1) age 0+, = 89 mm total length (TL); (2) age 1+, = 238 mm TL; and (3) age 2–3+, = 397 mm TL. As DO decreased from 8–10 mg l^-1 to < 0.5 mg l^-1, changes were evident in active time, water column activity, range of horizontal movement, food searching, and agonistic behavior. Age 0+ fish were most sensitive, moving up into the water column and swimming continuously as DO levels fell below 4.2 mg l^-1. Age 2–3+ fish were the least responsive, remaining on the substrate and increasing only their range of movement at concentrations below 3 mg l^-1. Responses of age 1 + fish were variable, possibly reflecting a transition stage between the younger and older fish. Common to all groups was the decrease and eventual cessation of food searching.     

Seasonal changes in low oxygen tolerance of fantail,Etheostoma flabellare,rainbow, E. caeruleum,and greenside,E. blennioides,darters

Synopsis The tolerance of fantail, rainbow, and greenside darters to low oxygen was determined by exposing fish to conditions of progressively decreasing oxygen levels and recording the oxygen concentration at which loss of equilibrium occurred. The greenside darter was least tolerant to low oxygen levels in summer, with loss of equilibrium occurring at a mean O₂ concentration of 3.39 mg l⁻¹. Tolerances then increased through spring. A similar trend was observed for the fantail darter, with the lowest tolerance occurring in summer (2.36 mg ⁻¹). and greatest tolerance in spring (2.03 mg l⁻¹). The rainbow darter exhibited its greatest tolerance to low oxygen in summer and spring (1.64 and 1.93 mg l⁻¹, respectively). Interspecific differences were greatest in summer, with greenside darters being the least tolerant to low oxygen levels and the rainbow darter being the most tolerant. No differences in tolerance among the species were noted in winter. The low oxygen tolerance exhibited in summer by the greenside darter may be due to a higher metabolic cost and a higher critical oxygen tension at maximal stream temperatures (>25° C). The observed differences in oxygen tolerance may influence the longitudinal distribution and habitat selection of darters, especially in the summer months.     

Zooplankton research in the North Sea

Summary Water types of the North Sea with different plankton are the thermally stratified northern and central regions with a relatively nutrient rich inflow of Atlantic water, a mixed region in the southern North Sea with a poor inflow of Channel water, and turbid narrow coastal zones with inflow of nutrient rich river water. Plankton studies reveal that the primary production starts early, in February, in the southern region, but is delayed in the coastal zones by turbidity. In stratified areas the algal spring bloom is delayed by mixing towards the greater depth and usually starts with the onset of thermal stratification. The spring bloom soon declines and the algae remain on a low density level in summer, presumably due to depletion of nutrients in the euphotic zone. The coastal zones and the frontal zones between mixed and stratified water have a relatively high summer primary production.The herbivores (mainly planktonic copepodes and the tunicateOikopleura dioica) grow and increase in number when the temperature rises and food is available. There is a considerable mismatch with the algal spring bloom, which comes too early and is too short in most regions. The best coincidence occurs in the coastal zones and maybe the frontal zones. Carnivores build high biomasses in late summer and fall in the coastal regions and compete with fish larvae for food and also kill many fish larvae. The large scyphomedusae are most important in this respect.The overall yearly primary production of the North Sea is estimated to be about 100 mg C.m^–2. The estimates for herbivores and fish are 20 and 1 mg C.m^–2. Considering a growth efficiency of 20%, the herbivores must consume all algae produced. The indication of a low consumption due to bad phenological coincidence in most regions leads to the assumption, that either primary production is underestimated or there is a considerable influx of organic matter from the Atlantic Ocean. During June–July 1979 the carnivore consumption was estimated in the coastal zone of the Southern Bight to be 39 mg C.m^–2.d^–1 at a copepod production of 20 mg C.m^–2.d^–1. Consumption by fish larvae and large jellyfish (Cyanea lamarckii) was 15% and 74%, respectively.It seems clear that the productivity of the North Sea depends highly on coastal and frontal zones, where herbivores find sufficient food at optimal growth conditions. Most organic matter will at the end be consumed by invertebrate carnivores, which urge fish populations to reproduce early in spring or to recruit at remote places.     

The endemic spring snail Pyrgulopsis montezumensis in a high CO2 environment: Importance of extreme chemical habitats as refugia

1. We examined the distribution of the endemic spring snail, Pyrgulopsis montezumensis, along a gradient of dissolved free CO₂ and on selected substrata in the collapsed travertine springmound of Montezuma Well, Arizona, U.S.A. 2. Dissolved CO₂ concentration ranged from 480 (SE ± 56) mg L^??1 near the bottom spring vents in the limnetic zone (12 m deep) of the well to < 20 mg L^??1 in an irrigation canal about 1400 m downstream from the well outlet. Spring snails occurred in habitats with 110–315 mg L^??1 dissolved CO₂. 3. Laboratory experiments showed that P. montezumensis tolerated a dissolved CO₂ concentration up to about 400 mg L^??1 for 11 days, but displayed 40% (SE ± 4) mortality after 3 days at 728 mg L^??1 and 100% mortality after 24 h at 1200 mg L^??1. We also measured 100% mortality after 10 days at ambient concentrations (< 10 mg L^??1) of dissolved CO₂. 4. Although the concentration of dissolved CO₂ was within the tolerance range for spring snails in the irrigation canal, inadequate substrata and increased predation probably restricted their distribution in the lower reaches of the canal. Both field measurements and laboratory selection experiments showed a significant (P < 0.001) preference for limestone substrata over submerged vegetation and fine sediments. 5. We propose that springs with high dissolved CO₂ may provide refugia from invertebrate and/or vertebrate predators not physiologically adjusted to the extreme chemical environment. These extreme chemical habitats probably reduce competition for resources and predation and allow resistant populations like P. montezumensis to attain high density.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.     

Effects of Nutrients,Fish, Charophytes and Algal Sediment Recruitment on the Phytoplankton Ecology of a Shallow Lake

The influence of nutrient levels, fish density and charophytes on the phytoplankton ecology of a shallow Mediterranean lake was studied by means of an in situ mesocosm experiment. Different levels of nutrients and fish were added over the course of an eight‐week experiment, during which charophytes were removed towards the end. After submerged plants were removed, phytoplankton biomass increased significantly in all the mesocosms, with a reduction of algal diversity and species richness and dominance of cyanobacteria. Cyanobacteria recruited from the sediment played an important role in sustaining planktonic populations of the dominant species. Oscillatorial species (Pseudanabaena galeata, Planktolyngbya limnetica) dominated at higher nutrient levels (0.5–1 mg L^–1 P and 5–10 mg L^–1 N) and chroococcal cyanobacteria (Merismopedia tenuissima) at lower nutrient levels. Density of planktivorous fish had little effect on the algal recruitment from the sediment and phytoplankton biomass and diversity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Utilization of metabolic scope in relation to feeding and activity by individual and grouped zebrafish, Brachydanio rerio (Hamilton-Buchanan)

Metabolic scope and its utilization in relation to feeding and activity were measured in individual and grouped zebrafish (weight range, 430–551 mg) at 24° C by respirometry. Mean maximum metabolic rate, induced by swimming to exhaustion, R_max(i), was 1223 (s.d. , 157) mg O₂, kg^?1 h^?1 for individuals. Standard metabolic rate, R_s. was 364 mg O₂ kg^?1 h^?1, as estimated by extrapolating to zero activity from measurements of unfed, spontaneously active individuals. Mean routine metabolic rate, R_rout, of individuals was 421 (s.d. , 58) mg O₂, kg_-1 h_-1. The mean voluntary maximum metabolic rate, R_max(v), following transfer of minimally exercised fish to the respirometer, was 1110 (s.d. , 83) mg O₂ kg ^?1 h^?1 for groups of six fish, and was not significantly different from the value measured for individuals, 1066 (s.d. , 122) mg O₂, kg^?1 h^?1. Grouped fish acclimated to the respirometer more slowly than individual fish and exhibited significantly higher R_rout, apparently a result of greater social interaction and activity in groups. Mean R_rout for groups was 560 (s.d. , 78) mg O₂, kg^?1 h^?1. While groups of zebrafish fed a ration of 5% wet body weight day^?1 exhibited consistently higher metabolic rates than fish fed rations of 2.5% wet body weight day^?1 the high ration group still used only a maximum of 77% of the metabolic scope. Zebrafish of the size studied do not appear to demonstrate a high degree of conflict in utilization of metabolic scope by different respiratory components. The metabolic rates measured for zebrafish are among the highest yet measured for fish of similar size and at similar temperatures.     

Seasonality in Nutrients and Phytoplankton Production in Two Shallow Lakes: Waigani Lake,Papua New Guinea,and Barton Broad,Norfolk, England

Waigani Lake, near Port Moresby, Papua New Guinea and Barton Broad, Norfolk, England are both shallow lakes nutrient-enriched from sewage effluent disposal. In Waigani Lake phytoplankton biomass varied seasonally with lower levels (100-200 mg chlorophyll α m⁻³) during the wet season increasing to over 400 mg chlorophyll α m⁻³ at the end of the dry season. Secchi disc depths varied between 0. 11 and 0. 34 m. Phytoplankton productivity in Waigani Lake was very high throughout the year (range: A_max 4,370-21,000 mg O₂ m⁻³ h⁻¹) but production was lower during the wet season (range: A_max 4,370-12,700 mg O₂ m⁻³ h⁻¹). High surface productivity was recorded from August to December except on sampling days when the weather was overcast. Productivity throughout the year declined rapidly with depth. Algal biomass in Barton Broad varied from 3-10 mg chlorophyll α m⁻³ in winter but increased in spring and was very high in summer (200-500 mg chlorophyll α m⁻³). Secchi disc depth varied from 0.21 m in August 1976 to 1.76 m in December. Phytoplankton production in Barton Broad was low in winter (range: A_max 247-1,250 mg O₂ m⁻³ h⁻¹) but increased markedly in spring and summer with the highest rate (A_max 6,850 mg O₂ m⁻³ h⁻¹) being recorded in August. Surface inhibition was observed during summer except when the weather was overcast. Seasonality in nutrients and phytoplankton in Waigani Lake appear to be related to rainfall. Nutrient concentrations in Barton Broad are more closely related to phytoplankton activity which, in turn, correlates with seasonality in solar radiation.     

Experimental treatments with diflubenzuron and deltamethrin of sea bass, Dicentrarchus labrax L., infected with the isopod, Ceratothoa oestroides

Sea bass with approximate average weights of 5 and 20 g were treated against Ceratothoa oestroides infection with: (i) medicated pellets of diflubenzuron PC90 at a dosage of 3 mg kg^?1 body weight (BW) per day for 14 days. Lice were counted at the beginning of treatment and 19 days after treatment. The drug cleared all lice in the treated group; in the control group, infection remained high 30 days after beginning the experiment. It was concluded that medicated pellets containing 3 mg kg^?1 BW diflubenzuron effectively cleared pre‐adult and adult stages of the isopod parasite over a 14‐day period. No adverse effects were recorded in treated sea bass during the trials and no reinfection occurred 15 days after end of the treatment. (ii) Deltamethrin by means of bath treatments in infected sea bass kept in experimental tanks at 20°C. Before treatment, toxicity on healthy fish was preliminarily assessed by testing five fish from each size group at concentrations of 30, 10, 5, 3, 1, 0.1, 0.05 and 0.01 mg L^?1 for 30 min. The therapeutic concentrations tested were: 10, 5, 3, 0.15, 0.1, and 0.05 μg L^?1 and assessed at 1, 24 and 48 h. Best results were achieved with the 10 μg L^?1 (0.01 mg L^?1) dose, where prevalence was reduced from 100 to 0% over 24 h in both large and small fish. No parasite recovery was observed at 48 h. The dose of 5 μg L^?1 reduced prevalence from 100 to 11.7% and to 0% for small and large fish, respectively. Finally, with the 3 μg L^?1 dose, prevalence was reduced from 100 to 37.5% (small fish) and to 13.3% (large fish). Lower doses were ineffective on the parasites at either 24 or 48 h.     

A halophilic thermotolerant Bacillus isolated from a marine hot spring able to produce a new exopolysaccharide

A halophilic, thermotolerant Bacillus strain (B3-15), isolated from water of a shallow, marine hot spring at Vulcano Island (Eolian Islands, Italy), produced an exocellular polysaccharide at 165 mg l^–1. It grew on kerosene as sole carbon source and was resistant to Cd²⁺, Zn²⁺, As²⁺ and Hg²⁺. From 16S rDNA analysis, strain B3-15 was related to B. licheniformis. The exopolysaccharide was a tetrasaccharide repeating unit essentially constituted by sugars having a manno-pyranosidic configuration.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Changes in branchial and intestinal osmoregulatory mechanisms and growth hormone levels during smolting in hatchery-reared and wild brown trout

Evidence of smolting was studied in Danish hatchery-reared brown trout Salmo trutta L. Twenty-four hour seawater (SW) challenge tests (28‰, 10°C) at regular intervals showed that maximal hypo-osmoregulatory ability developed within a 3–4-week period in March and April. The improved ability to regulate plasma osmolality, muscle water content and plasma total [Mg] developed asynchronously, indicating that developmental changes in the gill, the gastrointestinal system and the kidney may not necessarily concur during smolting. Gill Na⁺, K⁺-ATPase activity peaked in April at the time of optimal hypo-osmoregulatory ability. Na⁺, K⁺-ATPase a -subunit mRNA level in gills was unchanged from January until April, but decreased in May in parallel with a decrease in the activity of the enzyme. In the middle region of the intestine, Na⁺, K⁺-ATPase activity increased in February and remained high until April. In the posterior region of the intestine, the activity was stable from January until April after which it decreased. In vitro fluid transport capacitity, J_v, in the middle intestine fluctuated throughout the spring. In the posterior intestine, J_v was low until late March, when it increased fivefold until early May. Drinking rate in fish transferred to SW for 24 h surged during spring. Na⁺, K⁺-ATPase activity in the pyloric caeca was elevated from March until May, and increased in response to SW transfer in June, suggesting a hypo-osmoregulatory function of the pyloric caeca. Plasma GH levels surged in FW trout during spring, concurring with the increase in gill Na⁺, K⁺-ATPase activity and SW tolerance, but peaked in May when gill Na⁺, K⁺-ATPase activity and SW tolerance were regressing. GH levels were generally low in SW-challenged fish, and there was no consistent effect of 24-h SW exposure on GH levels. In wild anadromous trout, gill Na⁺, K⁺-ATPase activity varied seasonally as in hatchery-reared fish, but peaked at higher levels suggesting a more intense smolting in fish living in their natural environment.     

Observations on limnological conditions associated with a fish kill of Oreochromis niloticus in Lake Chivero following collapse of an algal bloom

Possible causes of deaths of Oreochromis niloticus in Lake Chivero were examined in relation to changes in limnological conditions monitored over a 25‐month period. The fish deaths coincided with the collapse of an algal bloom that had developed and builtup in the lake for 8 months. Chlorophyll a and dissolved oxygen increased to average concentrations of 42.4 μg l^?1 and 10.9 mg l^?1 respectively prior to the collapse of the bloom. Dissolved oxygen decreased when the bloom started to die off and coincided with the fish deaths when the average surface dissolved oxygen concentration in the lake was 3.9 mg l^?1 and was at a depth of 5 m <2 mg l^?1. Mortality probably resulted from depressed oxygen levels caused by the high oxygen demand from the massive algal die‐off and released algal toxins. This is the first time that die‐off of algae has been linked to fish‐kills in Lake Chivero as occurs in other hypereutrophic systems.