Stocking success of newly hatched pike evaluated by radioactive strontium (85Sr) marking

The stocking of newly hatched pike Esox lucius labelled with radioactive strontium (⁸⁵Sr) and later electrofishing of the same area was found to be a workable tool in assessing the success of pike stockings. ⁸⁵Sr‐labelled individuals constituted 96% of the 0+year pike catch from late summer electrofishing in the stocked littoral areas of the heavily regulated Lokka Reservoir. The density of 0+year pike reached 2·1 individuals 100 m⁻² in the stocked areas in comparison to 0·3 individuals 100 m⁻² in the reference areas. In the three other stocked lakes the proportion of labelled pike in the catch ranged from 0 to 42% in late summer. The results suggest that pike stockings are profitable in filling empty or nearly empty 0+year pike habitats of regulated lakes or other waterbodies, where the natural reproduction of pike has declined due to human activities.     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

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.     

Radioactive strontium (85Sr) in marking whitefish [Coregonus lavaretus (L.)] larvae and the dispersal of larvae from river to sea

Anadromous whitefish [ Coregonus lavaretus (L.)] yolk-sac larvae were marked with a radioactive strontium isotope, ⁸⁵Sr. Before marking the method was tested in accumulation-elimination tests using various strontium concentrations. The first-phase effective half-life of ⁸⁵Sr in yolk-sac larvae was 4 days. The mean ⁸⁵Sr radioactivity was 81 Bq per larva at the day of release and the half-life of the slow component was 51 days, so the strontium label was easily detected up to 60 days after marking. The larvae were released into the River Simojoki about 12 km upstream from the river mouth and recaptured from early May to the end of July. Marked larvae were found at the river mouth 12–13 days after release, while the last marked fish in the river were found at 16 days. It is likely that all leave the river within 2 to 3 weeks post-hatching. Two months after marking some larvae had attained a distance of 10 km from the river mouth.     

Factors affecting the survival of dace, Leuciscus leuciscus (L.), in the early post-hatching period

Young dace fry were stocked into nylon mesh cages at densities ranging from 0·044 to 7·230 1^-1, and the cages anchored in a backwater area where the fry gathered naturally. The fry began feeding on small organisms drifting into the cages 2-4 days after hatching. The growth rate of the fry was inversely proportional, and the death rate directly proportional, to initial density. Soon after the exhaustion of endogenous food reserves (as determined from unfed fry), there was a period of massive mortality at the highest initial densities, probably due to starvation. After 20 weeks, the cages stocked at the two highest initial densities contained the lowest biomass of fry. Transfer of fry to cages with a larger mesh size produced increased growth and 46% survival over 20 weeks at the lowest initial density. These fry reached an overwintering length of 35·5 mm compared with 48·0 mm for naturally occurring fry.     

δ13C of wood in growth-rings indicates cambial activity of drought-stressed trees of Eucalyptus globulus

1. Growth, density and δ¹³C of wood and leaf area were measured in two adjacent stands of 6 year-old Eucalyptus globulus growing in the 600–700 mm year^–1 rainfall region of south-western Australia. Study sites were identical except for differences in the availability of water owing to physical properties of soil profiles and location of sites within the landscape.
2. Abundance of ¹³C (expressed as δ¹³C) in wood of trees growing on the drought-prone site (– 24·8‰±1·4) was greater than in other trees (– 25·8‰±1·2, P <0·001) throughout the 6 years and, with further development, the δ¹³C signatures of wood may become useful indices of drought-susceptibility in plantations within a few years of establishment. The seasonal pattern of δ¹³C of wood appeared to reflect seasonal variation in water availability and duration of cambial activity.
3. Basic density of wood of trees growing on the more drought-prone site (496±14·0 kg m^–3) was reduced compared to other trees (554±5·3 kg m^–3, P <0·001). δ¹³C of wood across boundaries of growth-rings suggested that drought stopped cambial activity resulting in less production of late wood and less dense wood.
4. The stand growing on the drought-prone site had reduced growth, wood yield and leaf area but identical specific leaf area. Annual growth was correlated with the previous season's rainfall. Together, these results suggested that within the same evaporative climate, drought reduces growth primarily by reducing leaf area and that there is a lag between onset of drought and reduced productivity.     

Cannibalism in pike fry, Esox lucius L.: some experiments with fry densities

Pike fry were kept in 0.054-m³ tanks at densities of 50, 100 and 150 (277, 555, 833 fry m⁻²) for seven weeks during which the development of social and feeding behaviour was observed. Zooplankton, macro-invertebrates and perch fry were provided sequentially as food; the pike fry were allowed to feed ad libitum.
Zooplanktivorous fry stopped growing at 22 mm whilst, in the presence of abundant suitable alternative prey, 1–4% turned cannibalistic at 5 weeks of age; cannibals subsequently grew rapidly (mean 1.88 mm day⁻¹). Cannibalism ensued in all tanks when the ratio of predator size: prey size was c .2:1.
Fry tended to space-out evenly in the tanks with no overt aggression or territoriality. Behaviour was typified by remaining still for long periods, particularly subsequent to the onset of cannibalism. Cannibals were attracted by fry movements which often initiated attacks.
Daily per capita mortality rates showed no crowding effects before cannibalism but significant density-dependent mortality due to cannibals. Consumption rates of cannibals varied between 0.63 and 6.0 fry per cannibal per day. Cannibals accounted for 54–96% of daily mortality in the experimental tanks. These results are discussed in relation to proposed mechanisms of pike population density regulation.     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to trace metal mixtures in soft water

Freshly fertilized ova of brown trout, Salmo trutta L., were exposed to all possible mixtures of Al (6000 nmol 1¹), Cu (80 nmol 1⁻¹), Pb (50 nmol 1⁻¹) and Zn (300 nmol 1 ¹). In a separate experiment, newly hatched brown trout yolk-sac fry were exposed to Mn (1500 nmol 1⁻¹), Fe (2500 nmol 1 ¹), Ni (200 nmol 1⁻¹) or Cd (4 nmol 1 ¹), separately, and in mixtures with either Al or Cu. Both experiments were conducted in flowing, artificial softwater media nominally at pH 5.6 [Ca] 20 μmol 1 ¹ and 10° C.
Mortalities were high in fry subjected to treatments which contained both Al and Cu (31–72%), and to the Cu + Fe treatment (78%) compared with those from the other trace metal mixtures (0–22%). In all the treatments tested, fry exposed to trace metal mixtures containing Al and/or Cu had reduced whole body Ca, Na and K content, and seriously impaired skeletal calcification. Whole body Mg content was variable. In trace metal mixtures which contained Cu but not Al, the effects on fry survival and whole body mineral content were in general more deleterious than the corresponding mixtures but with Al present rather than Cu. The presence of Pb and/or Zn in mixtures with Al and/or Cu had a slight ameliorative effect in terms both of fry survival and whole body mineral content.     

Stable isotopes of carbon and nitrogen as indicators of diet and trophic structure of the fish community in a shallow hypereutrophic lake

Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes were employed to elucidate energy flows and trophic interactions in Lake Apopka, a hypereutrophic lake in central Florida, U.S.A. Isotope compositions of lake biota ranged from −27·1 to −3·0‰ for δ¹³C, and from 3·7 to 13·9‰ for δ¹⁵N. The food web was based primarily on plankton production with diatoms, Microcystis and zooplankton dominating the diet of fish. Carbon isotope evidence showed that pico- and nano-phytoplankton were not a direct carbon source for fish, but were important to zooplankton. δ¹⁵N mass balance estimates indicated that planktivorous fish obtained 48–85% of their diets from zooplankton. The ∼3‰ range of δ¹⁵N in gizzard shad reflected increasing dependence on zooplankton as fish grew whereas the positive relationship between total length and δ¹⁵N of largemouth bass reflected increasing predation on larger planktivorous fish with growth. The broad ranges of δ¹³C (−25·9 to −9·5‰) and δ¹⁵N (5·8 to 14·4‰) of blue tilapia were indicators of diet diversity. Two presumed omnivores (brown bullhead and white catfish) and piscivores (black crappie, largemouth bass and Florida gar) were found to depend on planktivorous fish. However, stable isotope data revealed no trophic links between blue tilapia, an abundant fish in the near-shore area, and piscivores.     

Survival and sublethal responses of early life stages of pike exposed to low pH in artificial post-mining lake water

The threshold pH for survival of early life stages of pike Esox lucius in post-mining lakes was determined in a laboratory experiment using artificial water characterized by high concentrations of dissolved Ca, Al, Fe, Mn and SO2/4⁻. At pH 3·50–4·00, high mortality was observed before hatching. At pH 4·00 and 4·25, hatching rates were reduced compared with the controls (pH 7·40), and many embryos died in a partly hatched state. Hatching success of embryos exposed to pH levels of 4·50 or higher was not affected. However, at pH 5·00 many newly hatched embryos were deformed. Furthermore, pike exposed to pH 4·00–5·00 did not start feeding. At pH 4·75 and below, mortality increased to 100%, and at pH 5·00, only few eleutheroembryos which were in extremely poor condition survived to the end of the experiment. At pH 5·50, survival was in the same range as in the control group, but growth was reduced. Therefore, early life stages of pike are expected to survive in Lustian post-mining lakes when a pH of 5·50 and above is reached and maintained.     

Stable isotope profiles of partially migratory salmonid populations in Atlantic rivers of Patagonia

In the present study, profiles of stable isotope composition were characterized for two species with partially migratory populations in rivers along the latitudinal gradient of Patagonia, brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss . The effects of factors ( e.g. ontogeny of fishes, location, species and fasting) that may influence the stable isotope analysis (SIA) were evaluated, as was SIA evaluated as a tool to assign individual fish to their corresponding ecotype. Anadromous fishes exhibited enriched δ¹⁵N (15·2 ± 1·0‰; mean ± s . d .) and δ¹³C (−19·2 ± 1·3‰) relative to resident fishes'δ¹⁵N (8·8 ± 1·1‰) and δ¹³C (−23·2 ± 2·5‰). For both species, the difference in δ¹⁵N was larger between resident (range 6·8–10·7‰) and anadromous (range 14·3–17·8‰) fishes than that in δ¹³C. Values of δ¹³C, while not as dramatically contrasting in rainbow trout, provided a powerful anadromy marker for brown trout in the region. Increases were found in both δ¹⁵N and δ¹³C during the spawning migration of anadromous rainbow trout, most likely due to fasting. Differences in stable isotopes between location, size and species were found, suggesting different stable isotopes base levels in freshwater environments and different trophic levels and feeding location of anadromous populations. The SIA was demonstrated as a powerful tool for ecotype discrimination in Patagonian Rivers, overriding any effect of sampling location, size or species.     

Gastric evacuation rates and daily ration of piscivorous coho salmon, Oncorhynchus kisutch Walbaum

Effects of temperature and meal size on gastric evacuation rates of juvenile coho salmon, Oncorhynchus kisutch , consuming sockeye salmon, O. nerka , fry were examined and used in the estimation of daily meal, daily ration and number of fry consumed by coho in Chignik Lake, Alaska. Evacuation of fry by coho was best described by a negative exponential model (average R² = 0.93). A square root model also provided a good fit (average R² = 0·93), but the y-intercepts deviated more from the expected value than did the y-intercepts of the exponential model. The effect of temperature ( T , 5–13° C) and meal size (MS, 0·166–0·367 g) on the exponential evacuation rate (r_e, h^-1) could be described as
In the lake, coho fed continuously during the 24-h period in early June 1986 and 1987. Estimates of daily meal and ration of coho calculated by the Eggers method and the geometric mean of prey weight ranged from 0·224 to 0·435 g (2.1–4.4% body wt) depending on location and year. The Elliott & Persson method provided similar estimates of food consumption, whereas estimates based on the Pennington method and square root evacuation of prey differed from the exponential models. Sockeye fry represented 93% of the total prey weight. The average number of sockeye fry consumed per coho per 24 h, based on the arithmetic mean of prey weight, was 3·0–3·9 fry.     

Automated concentration and recovery of micro-organisms from drinking water using dead-end ultrafiltration

Aims:  Concentration of pathogens diluted in large volumes of water is necessary for their detection. An automated concentration system placed online in drinking water distribution systems would facilitate detection and mitigate the risk to public health.
Methods and Results:  A prototype concentrator based on dead-end hollow fibre ultrafiltration was used to concentrate Bacillus atrophaeus spores directly from tap water. Backflush was used to recover accumulated particulates for analysis. In field tests conducted on a water utility distribution system, 3·2 × 10⁴–1·4 × 10⁶ CFU ml⁻¹ (6·1 × 10⁶–3·0 × 10⁸ CFU) were recovered from the filter when 2·9 × 10⁷–1·0 × 10⁹ CFU were spiked into the system. Per cent recovery ranged from 21% to 68% for flow volumes of 15–21 l. Tests using spore influent levels <10 CFU l⁻¹ (spike < 1000 CFU) yielded 23–40% recovery for volumes >100 l.
Conclusions:  B. atrophaeus spores at levels <10 CFU l⁻¹ were concentrated directly from tap water using an automated dead-end hollow-fibre ultrafiltration system.
Significance and Impact of the Study:  The prototype concentrator represents a critical step towards an autonomous system that could be installed in drinking water distribution lines or other critical water lines to facilitate monitoring. Recovered samples can be analysed using standard or rapid biosensor methods.     

The use of the bacteriocin, nisin, as a preservative in ricotta-type cheeses to control the food-borne pathogen Listeria monocytogenes

The efficacy of nisin to control the food-borne pathogen Listeria monocytogenes in ricotta-type cheeses over long storage (70 d) at 6–8°C was determined. Cheeses were prepared from unpasteurized milk by direct acidification with acetic acid (final pH 5·9) and/or calcium chloride addition during heat treatment. Nisin was added in the commercial form of Nisaplin^® pre-production to the milk. Each batch of cheese was inoculated with 10²–10³ cfu g⁻¹ of a five-strain cocktail of L. monocytogenes before storage. Shelf-life analysis demonstrated that incorporation of nisin at a level of 2·5 mg l⁻¹ could effectively inhibit the growth of L. monocytogenes for a period of 8 weeks or more (dependent on cheese type). Cheese made without the addition of nisin contained unsafe levels of the organism within 1–2 weeks of incubation. Measurement of initial and residual nisin indicated a high level of retention over the 10-week incubation period at 6–8°C, with only 10–32% nisin loss.     

Distribution of Synechococcus spp. determined by immunofluorescent assay

By using two polyclonal antisera against WH 7803 strain (Synechococcus sp.) and WH 5701 strain (Synechococcus bacillaris) it is possible to detect and to enumerate cells of the two cyanobacterial serogroups. The immunofluorescence technique was used to study the distribution of the two serogroups in the estuarine, coastal and upwelling waters of the Mediterranean Sea surrounding Messina. In the estuarine waters of the Alcantara River (Ionian Sea), the WH 7803 serogroup was present at a concentration in the order of 10² cells ml⁻¹ and the WH 5701 serogroup at a concentration of 5·5 × 10² cellsml⁻¹. In the coastal waters of Messina, where urban and industrial wastes are usuallydumped, the concentration of total phycoerythrin- Synechococcus ranged from 1·3 × 10² to 4·1 × 10³ cells ml⁻¹; the WH 7803 serogroup accounted for 50–94% of the totalpopulation in Ionian stations, whereas the WH 5701 serogroup ranged from1·4 × 10¹ to6·7 × 102cells ml⁻¹. In the upwelling area (Straits of Messina) bothserogroups were found. Vertical distribution of two Synechococcus strains had anopposite trend and their concentrations were of the order of 10¹–10²cells ml⁻¹. Theuse of the Scan laser system allows both autofluorescent and labelled organismsto be distinguished in a preparation for optical microscopy. It also allows false-positivecells to be distinguished.     

Isolation of Yersinia enterocolitica-resembling Organisms and Alteromonas putrefaciens from Vacuum-Packed Chilled Beef Cuts

Yersinia enterocolitica -resembling organisms were found at levels of 10⁷/g on a high pH (pH ≧ 6·0) vacuum-packaged beef striploin held for 6 weeks at 0·2°C, but did not exceed 10⁵/g on normal pH (pH < 6·0) striploins held for 10 weeks. Gram negative bacteria that produced H₂S on peptone iron agar were isolated from high pH vacuum packed striploins. These organisms were identified as Alteromonas putrefaciens . They attained levels of about 10⁷/g in 6 weeks at 0–2°C, at which time greening of the fat surface and 'drip'had occurred. On meat of normal pH, counts of A. putrefaciens were less than 10⁴/g after 6 weeks and no greening was evident.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Production of amylase by the intestinal microflora in cultured freshwater fish

The amylase-producing ability of the intestinal microflora in cultured specimens of ayu, carp, channel catfish, Japanese eel and tilapia was determined. Mean viable counts of aerobes and anaerobes ranged from 1·1×10⁶ to 3·7×10⁸ cfu g⁻¹ and from 1·3×10³ to 1·6×10⁸ cfu g⁻¹, respectively. Aeromonas spp. and Bacteroidaceae were predominant in four to five fish species. Of 206 strains examined, 65 (31·6%) produced ≥0·01 U amylase ml⁻¹. The percentage of producers differed among families and genera of bacteria and fish species. While 56% of the anaerobes produced amylase, only 20% of the aerobes did. More than 50% of Aeromonas , Bacteroidaceae and Clostridium strains produced amylase efficiently while Acinetobacter , coryneforms, Enterobacteriaceae, Moraxella , Plesiomonas and Streptococcus strains did not. High amylase production (≥0·05 U ml⁻¹) was found in 12 strains, 11 from Aeromonas and one Pseudomonas . The percentage of high amylase producers in Japanese eel was lower than the other four fish (2–30%). These results strongly suggest that the amylase produced by the intestinal microflora play an important role in the digestion of starch in freshwater fish to some extent.     

A one step PCR-based method for the detection of economically important soft rot Erwinia species on micropropagated potato plants

A simple, rapid and sensitive PCR-based method was developed for the detection of all five subspecies of Erwinia carotovora , including subsp. carotovora and subsp. atroseptica , and all pathovars/biovars of Erwinia chrysanthemi , on plant tissue culture material. Primers SR3F and SR1cR, based on a conserved region of the 16S rRNA gene, amplified a DNA fragment of 119 bp from all 65 such strains tested. Detection limits of the method in vitro were 2·0 × 10²–3·4 × 10³ cfu ml⁻¹ (equivalent to 1–17 cfu per PCR) and, following extraction of genomic DNA from plant extract, detection limits were 2·3 × 10²–1·9 × 10⁴ cfu per microplant sample (equivalent to 5 cfu – 3·8 × 10² cfu per PCR). To improve the sensitivity of the method in planta , to obviate the need for complex and laborious DNA extractions, and to remove inhibitory substances present in the plant extract, an enrichment step was included prior to PCR. Following enrichment, the sensitivity of detection was <10 cfu per microplant sample. This method provides the first sensitive means of detecting latent infection caused by several economically important soft rot erwinias simultaneously on potato tissue culture material.     

Seasonal changes in some blood chemistry parameters and in relative liver and gonad weights of pike (Esox lucius L.) from the River Danube

Samples from a natural population of pike (Esox lucius L.) from the River Danube were used in a 12-month study to determine seasonal variations in biochemical parameters of pike blood sera, hepatosomatic index (HSI) and gonadosomatic index (GSI). The ranges of enzyme activities for sample means were: aspartate aminotransferase (ASAT) 252.0–583.8 U 1⁻¹, alanine aminotransferase (ALAT) 4.9–11 -2 U1 and alkaline phosphatase (AP) 39.5–91.8 U1⁻¹. The ranges of other parameters analysed in serum were total protein 27.7–40.1 g 1 ¹, urea 0.57–l.52 mmol 1 ¹ and creatinine 21.2–118.6 μmol 1 ¹. The range of sample means for HSI and GSI were 1.28–4.16 and 0.07–20.2 respectively. Temperature ranged from 4.5 to 23.5°C. The activity of serum AP was positively correlated to water temperature in males only, while urea and creatinine showed a positive correlation to water temperature in individuals of both sexes. GSI was correlated significantly with HSI in females. Total protein reached the lowest values during the spawning period, while creatinine levels depended on both the sex and season.