Productivity of a herbivorous pupfish population (Cyprinodon nevadensis) in a warm desert stream

Production and food intake by an herbivorous pupfish population ( Cyprinodon nevadensis amargosae ) living in the outflow of a thermal artesian well (Tecopa Bore) near Death Valley, California is described. Water issues from the ground at 47.5° C and cools 8.12° C before leaving the study area 300 m from the source. High stream temperatures restricted the pupfish population to some 41 % of the study area, with a resulting mean density of 89 individuals m⁻² (range = 13 to 196m⁻²). Biomass estimates ranged from 7 kcal m⁻² to 42 kcal m⁻². The mean annual standing crop of pupfishes (24 kcal m⁻²) turned over about five times annually. Growth rates were highest in juveniles (♂= 9.5% day⁻¹) and slowest in large adults (♀= 08% day⁻¹). Monthly production ranged from 22 kcal m⁻² in September to 3 kcal m⁻² in July and August. Pupfish in Tecopa Bore fed on algae and detritus, ingesting 1941 kcal m⁻² yr⁻¹ or 17.5% of the annual net primary production. 119 kcal m⁻² yr⁻¹ was deposited in growth. This latter value is approximately ten times greater than values previously reported for large carnivorous fishes but is comparable lo values reported for herbivorous fishes under pond culture.     

The effect of turbidity and illumination on the reaction distance and search time of the marine planktivore Gobiusculus flavescens

Both reduced illumination and increased turbidity caused a significant reduction in reaction distance of Gobiusculus flavescens . The longest reaction distance, 18.9 cm for larger prey (Calanus finmarchicus) , occurred at a light level of 80 μmol m ⁻² s ⁻¹ compared to 12.9 cm for a smaller prey (Acartia clausi) at 8 μmol m⁻² s⁻¹. Above a light saturation level of 10 μmol m⁻² s⁻¹, additional light had little influence on reaction distance. In the turbidity experiments, the longest reaction distances were measured at turbidity levels of 10–20 JTU. Prey size influenced reaction distance at all tested light levels. Search time was influenced by prey size only at low illumination. With increasing turbidity, reaction distance to a group of prey was longer than to one prey.     

Sample sizes for length and density estimation of 0+ fish when using point sampling by electrofishing

Standard lengths of cyprinids at several sites in the River Great Ouse, England, were compared between catches taken using a conventional 15 × 3 m micromesh seine (pore diameter 2 mm) and using point sampling by electrofishing (PSE). No statistically significant differences in sites were found in six out of 10 trials. In nine out of 10 trials, the difference between the mean lengths differed by <1 mm. No serial bias was found between PSE and seine netting for cyprinid fishes between 14 and 100 mm SL, although variation between size classes was high, owing to small sample sizes. The coefficient of variation in fish length with size tended to increase with the age of 0+ Rutilus rutilus . The relationship between sample size (n) and variance ( s² ) was explained by s ²=13·9 n ^−1·24. Sampling more than 30 fish resulted in little increase in precision. The relationship between the mean catch per site (̄) and the variance of the mean estimate was log s ²=1·6039 log ̄ +0·973. The number of samples required to estimate density within a given variance range was: n =9·33 ̄ ^1·6–2 CV_̄ ⁻². Given the high variance-mean ratio, great care should be taken when interpreting density data collected using PSE, and 50 point samples is the minimum required for density estimation.     

Comparative effects of long-term hypoxia on growth, feeding and oxygen consumption in juvenile turbot and European sea bass

When juvenile turbot Scophthalmus maximus and sea bass Dicentrarchus labrax were fed to satiation, growth and food intake were depressed under hypoxia (3·2±0·3 and 4·5±0·2 mg O₂ l^-1). However, no significant difference in growth was observed between fishes maintained in hypoxia and fed to satiation and fishes reared in normoxia (7·4±0·3 mg O₂ l^-1) and fed restricted rations (same food intake of fishes at 3·2 mg O₂ l^-1). Routine oxygen consumption of fishes fed to satiation was higher in normoxia than in hypoxia due to the decrease in food intake in the latter. Of the physiological parameters measured, no significant changes were observed in the two species maintained in hypoxia. This study confirms the significant interaction between environmental oxygen concentrations, feeding and growth in fishes. Decrease in food intake could be an indirect mechanism by which prolonged hypoxia reduces growth in turbot and sea bass, and may be a way to reduce energy and thus oxygen demand.     

Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

Attraction of zebrafish, Brachydanio rerio, to alanine and its suppression by copper

Preference responses of zebrafish to 10⁻³, 10⁻⁴ and 10⁻⁵M alanine (Ala) were concentration- dependent. Behavioural responses to copper (Cu) and Cu + Ala mixtures were also assessed. Zebrafish avoided 100 and 10 μg Cu l⁻¹, but not 1 μg l⁻¹. Mixtures of 10⁻³ m Ala+ 100 μg Cu l⁻¹ and 10 ⁴ M Ala + 10 μg Cu 1⁻¹ were avoided as intensely as was Cu alone. Responses to 10⁻³ M Ala + 10 or 1 μg Cu l⁻¹ and 10 ⁴ M Ala +1 μg Cu l⁻¹ did not differ statistically from controls (no detectable preference or avoidance). These results demonstrate, firstly, that a concentration of a pollutant avoided by itself (10 μg Cu l⁻¹) may not be avoided when encountered with an attractant chemical stimulus (Ala) and may suppress the preference for an attractant stimulus, and secondly, that a concentration of a pollutant not avoided by itself and not considered deleterious (1 μg Cu l⁻¹) suppresses attraction to Ala (an important constituent of prey odours for many fishes).     

Depth equilibration by two predatory cichlid fish from Lake Malawi

The cichlid fish, Haplochromis polystigma and Haplochromis livingstonii are piscivorous ambush predators endemic to Lake Malawi, Africa. Experimentally it was found that large adult H. livingstonii could equilibrate to 38 m, but that juveniles were restricted to shallower depths. Mean depth attained by 8 H. polystigma was 45 m but two individuals exceeded the maximum simulated depth (59 m). H. livingstonii had a mean equilibration rate of 4–7 m day⁻¹ for the first 10 m declining to 2·4 m day⁻¹ thereafter. The mean rate of descent for H. polystigma was 3·8 m day⁻¹ for the first 10 m and 2·8 m day⁻¹ thereafter. The fish were decompressed at a rate of a 20% decrease every 12 h. Although cichlid fishes occur down to 200 m depth in Lake Malawi, experimental and field data indicate that the depth distribution of individual species is restricted and that the restriction is largely related to swimbladder physiology. All cichlid species so far tested equilibrate slowly to depth (2 to 5 m a day) and are not capable of rapid decompression.     

A method for long-term measurement of respiration in intertidal fishes during simulated intertidal conditions

Aquatic and aerial respiration of the amphibious fishes Lipophrys pholis and Periophthalmus barbarus were examined using a newly designed flow-through respirometer system. The system allowed long-term measurements of oxygen consumption and carbon dioxide release during periods of aquatic and aerial respiration. The M o ₂ of L. pholis , measured at 15° C, was 2·1 μmol O₂ g^–1 h^–1 during aquatic and 1·99 μmol O₂ g^–1 h^–1 during aerial exposure. The corresponding values of the M co₂ were 1.67 and 1.59 μmol O₂ g^–1 h^–1 respectively, giving an aquatic respiratory exchange ratio (RER) of 0·80 and an aerial RER of 0·79. The M o₂ of P. barbarus , measured at 28°C, was 4·05 μmol O₂ g^–1 h^–1 during aquatic and 3·44 μmol O₂ g^–1 h^–1 during aerial exposure. The corresponding values of the Mco₂ were 3·29 μmol CO₂ g^–1 h^–1 and 2·63 μmol CO₂ g^–1 h^–1 respectively, giving an aquatic RER of 0·81 and an aerial RER of 0·77. While exposed to air for at least 10 h, both species showed no decrease in metabolic rate or carbon dioxide release. The RER of these fishes equalled their respiratory quotient. After re-immersion an increased oxygen consumption, due to the payment of an oxygen debt, could not be detected.     

A comparison of a new campylobacter selective medium (CAT) with membrane filtration for the isolation of thermophilic campylobacters including Campylobacter upsaliensis

The newly developed CAT campylobacter selective medium employing the blood-free charcoal-based agar containing cefoperazone (8 mg I⁻¹), amphotericin (10 mg I⁻¹) and teicoplanin (4 mg I⁻¹) was compared with the membrane filtration culture technique for isolation of Campylobacter spp. including Camp. upsaliensis. Nine hundred and fifty human, 275 dog and 65 cat faeces (in which modified CCDA medium was also compared) were tested. In addition, the recovery of Camp. upsaliensis from pure cultures and from spiked human faeces was examined after membrane filtration. A 50-fold reduction in recovery after filtration using the 0·65 μm filters and a 150-fold reduction using the 0·45 μm filters was found. Recovery of Camp. upsaliensis from spiked faeces was considerably improved using the CAT medium compared with filtration, especially with the lower concentration of organisms (approx. 10⁴ cfu ml⁻¹). Campylobacter upsaliensis was recovered from 91 specimens of animal faeces, with CCDA recovering 26 isolates (29%), CAT recovering 76 isolates (84%) and membrane filtration (0·65 μm) recovering 82 isolates (90%). CAT selective agar was found to be a suitable medium for the isolation of thermophilic campylobacters including Camp. upsaliensis from faecal samples.     

METHYLATION OF E. COLI TRANSFER RIBONUCLEIC ACIDS BY A tRNA ADENINE-l-METHYLTRANSFERASE FROM RAT BRAIN CORTEX AND BULK-ISOLATED NEURONS

Abstract— Brain cortices or bulk-isolated neuronal cell bodies prepared from cortices of 8-day old male rats were used as the source of a l-methyl adenine-specific tRNA methyltransferase (tRNA-AMT). Ammonium sulfate fractionation and chromatography on spheroidal hydroxylapatite and Sephadex G-200 yielded an 80-fold purified enzyme, as determined by using E. coli bulk tRNA as substrate. The kinetic parameters of tRNA-AMT for the substrate S -adenosyl- l -methionine (SAM) ( K _m= 6 μM) and the inhibitor, S -adenosyl- l -homocysteine (SAH) ( K _i= 3.4 μ m ) were determined and several SAH analogs tested as inhibitors. S -Adenosyl- l -cysteine (SAC) ( 10 ^-4 m ) and S -adenosyl- d -homocysteine (SADH) (10^-4 m ) produced a 35 and a 21% reduction in enzyme activity, respectively. The effects of Mg²⁺, NH₄⁺ acetate and of the polyamines spermine, putrescine and spermidine on the brain tRNA-AMT mimicked the effects of these agents on hepatic tRNA-AMT (G lick et al , 1975).
Comparing the ability of cerebral tRNA-AMT to methylate E. coli tRNA^glu2, tRNA^val, tRNA^phe and bulk tRNA revealed tRNA^glu2 as the best and tRNA^phe as the least effective substrate.
tRNA-AMT prepared from neuronal cell bodies showed closely similar characteristics to the cortical enzyme. A comparison of the activities of tRNA-AMT in neurons and glial cells revealed higher values in the former.     

Compartments of Labeled and Endogenous γ-Aminobutyric Acid Giving Rise to Release Evoked by Potassium or Veratridine in Rat Cortical Slices

Abstract— To establish compartments involved in depolarization-induced release of γ-aminobutyric acid (GABA) in rat brain slices, the amount of exogenous labeled and endogenous GABA released and retained was followed during 48 min exposure to 50 m m -K⁺ or to 50 μ m -veratridine. Endogenous GABA was measured with high performance liquid chromatography. The presence of 10 μ m -aminooxyacetic acid throughout prevented both the metabolism of GABA and the formation of endogenous GABA due to depolarization. During super-fusion with 50 m m -K⁺ and 2.6 m m -Ca²⁺ the efflux of labeled and endogenous GABA after an initial large increase declined to 10% of the highest value with constant and identical rates. Kinetic analysis of efflux showed that 10% of endogenous and 25% of labeled GABA present is available for release by high K⁺ and Ca²⁺. In the absence of Ca²⁺, release by high K⁺ of both labeled and endogenous GABA was nearly suppressed. Veratridine, unlike high K⁺, caused an efflux which declined with an initial fast and late very slow phase. The slow efflux by veratridine was doubled in the absence of Ca²⁺. Exposure to veratridine in the absence of Ca²⁺ during 120 min released nearly 70% of labeled and endogenous GABA present. Results suggest that only about 0.25 μmol g⁻¹ endogenous GABA is the source of physiological Ca²⁺-dependent release, while much of the remaining GABA present is released only under unphysiological conditions.     

Constitutive mineralization of low concentrations of the herbicide linuron by a Variovorax sp. strain

The mineralization of the herbicide linuron at concentrations of μg and mg L⁻¹ was studied in liquid batch experiments with Variovorax sp. strain SRS16. The strain was highly efficient at mineralizing a range of linuron concentrations (0.002–10 mg L⁻¹) with 20–60% of the added ¹⁴C-ring-labeled linuron metabolized to ¹⁴CO₂ within hours to days depending on the initial linuron concentration and incubation period. At mg L⁻¹ linuron concentrations the mineralization activity by SRS16 was inducible and a shift to constitutive mineralization activity was apparent with a reduction in the linuron concentration to μg L⁻¹ levels. This study revealed that strain SRS16 is a promising candidate for bioaugmentation of water or soil resources contaminated with low linuron concentrations.     

Sensitivity of Bacillus coagulans spores to combinations of high hydrostatic pressure, heat, acidity and nisin

We investigated the combined effects of pressure, temperature, pH, initial spore concentration and the presence of nisin on the survival of spores of Bacillus coagulans. Spores were more sensitive to pressure both at lower pH and at higher treatment temperatures. An additional 1.5-log₁₀ reduction in cfu ml^-1 was observed when pH was lowered from 7.0 to 4.0 during pressurization at 400 Mpa and 45°C. A 4-log₁₀ cfu ml^-1 reduction was observed when the temperature was increased from 25°C to 70°C during pressurization at 400 Mpa. The spores were sensitive to nisin at concentrations as low as 0.2 IU ml^-1. At least a 6-log₁₀ reduction was generally achieved with pressurization at 400 Mpa in pH 4.0 buffer at 70°C for 30 min when plated in nutrient agar containing 0.8 IU ml^-1 nisin.     

Effect of high-temperature, short-time (HTST) pasteurization on milk containing low numbers of Mycobacterium paratuberculosis

The efficacy of high-temperature, short-time (HTST) pasteurization (72 °C/15 s) when low numbers (≤ 10³ cfu ml ⁻¹ ) of Mycobacterium paratuberculosis are present in milk was investigated. Raw cows' milk spiked with Myco. paratuberculosis (10³ cfu ml⁻¹, 10² cfu ml⁻¹, 10 cfu ml⁻¹, and 10 cfu 50 ml⁻¹) was subjected to HTST pasteurization using laboratory pasteurizing units. Ten bovine strains of Myco. paratuberculosis were tested in triplicate. Culture in BACTEC Middlebrook 12B radiometric medium detected acid-fast survivors in 14·8% and 10% of HTST-pasteurized milk samples at the 10³ and 10² cfu ml⁻¹ inoculum levels, respectively, whereas conventional culture on Herrold's egg yolk medium containing mycobactin J detected acid-fast survivors in only 3·7% and 6·7% of the same milk samples. IS900-based PCR confirmed that these acid-fast survivors were Myco. paratuberculosis . No viable Myco. paratuberculosis were isolated from HTST-pasteurized milk initially containing either 10 cfu ml⁻¹ or 10 cfu 50 ml⁻¹.     

Ontogenetic changes in potassium transport in xylem of tomato

The influence of plant ontogeny on xylem exudate K⁺ concentrations and K⁺ transport to the shoot was studied in both nutrient-solution and field-grown tomato plants ( Lycopersicon esculentum ).
K⁺ concentrations in xylem exudate from decapitated plants decreased during tomato plant development from a high of 12 m M to a low of 5 m M . In the nutrient-solution plants, the most rapid decline occurred during the vegetative growth phase, while in field-grown plants, the xylem K⁺ concentrations remained high during an-thesis and then subsequently declined. The rapid decline in nutrient-solution plants might be related to a decrease in the absorptive efficiency of the root system. In field-grown plants, a reduction in the availability of assimilates to the root might account in part for the decrease in xylem exudate K⁺ concentrations. The volume (ml h⁻¹ plant⁻¹) and the net rates of K⁺ exudation (mmol h⁻¹ plant⁻¹) decreased dramatically as the fruits approached maturity. Since only a small reduction in xylem exudate K⁺ concentrations occurred during fruiting, the hydraulic conductivity of the root system decreased as the tomato plants aged. It is proposed that the ontogenetic changes in xylem transport of K⁺ contribute to a reduction in leaf free space K⁺ concentration which would explain the decline in tomato leaf K⁺ concentrations.     

Transgenerational marking of freshwater fishes with enriched stable isotopes: a tool for fisheries management and research

A promising new method of marking larval freshwater fishes with enriched stable isotopes by means of injecting the maternal parent with the marking agent was investigated. The ¹³⁸Ba:¹³⁷Ba ratios in the otoliths of larval golden perch Macquaria ambigua were compared to determine the effect of injecting female broodstock with different dosages of enriched ¹³⁷Ba at various times before spawning. There was 100% mark success in the progeny of fish injected with 20 μg g⁻¹ of enriched ¹³⁷Ba 24 h before inducing spawning with hormones and 40 μg g⁻¹ administered at the same time as inducement of spawning. Injection of 40 μg g⁻¹ enriched ¹³⁷Ba 21 days before spawning resulted in only 81% mark success and suggests rapid elimination of barium in M. ambigua . Injection with enriched ¹³⁷Ba did not significantly affect the fertilization rate, number of fertilized eggs or hatching rate compared with long-term hatchery records. These results suggest that transgenerational marking is an effective and affordable means of mass-marking larval fishes. Thousands of larval fishes can be permanently marked with a unique artificial isotopic mark via a single injection into the maternal parent, thus avoiding the handling of individual fishes or having to deal with chemical baths. Because no single mark or tagging method is suitable for all situations, transgenerational marking with enriched stable isotopes provides another method for researchers and managers to discriminate both hatchery-reared and wild fishes.     

The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Yolk-sac pike fry were stocked at densities of 0.74 – 81.4 m⁻² in two ponds, each divided into eight sectors (mean area 155.8 m²). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size-range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density-independent but switched by late June/July to density-dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May-July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm⁻² and in Pond 2 was 3.49gm⁻².
Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m⁻².
Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m⁻² is advised if large, density-dependent mortalities are to be avoided.     

A light intensity threshold for schooling in the Atlantic mackerel, Scomber scombrus

The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10⁻¹⁰μEs⁻¹ m⁻². Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10⁻⁶μEs⁻¹ m⁻²) mackerel always formed a single school, whereas at lower levels (1.8 × 10⁻⁸μEs⁻¹ m⁻²) they swam as individuals. At light levels down to 1.0 × 10⁻⁶μEs⁻¹ m⁻² the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10⁻⁷μEs⁻¹ m⁻², both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10⁻⁹μEs⁻¹ m⁻². The results are discussed in terms of ambient light conditions in the sea.