Seasonal dynamics in abundance, development and pattern of infection of Bunodera luciopercae (Müller) in perch, Perca fluviatilis L. from an oligotrophic lake in Norway

Samples of perch, Perca fluviatilis L., were examined monthly for the presence of the intestinal trematode Bunodera luciopercae (Müller). Marked seasonal cycles in incidence and intensity of infection were found, with a minimum level in July, when all the fish examined were free of the fluke, and a maximum level in February. Five developmental stages of the fluke were recognized and the seasonal changes in the percentage distribution of these stages were studied. Infective larvae were found in the period August–March, with a peak in January. Gravid worms were mainly found in the period May-June. The frequency distribution of parasite counts were over-dispersed and followed the negative binomial distribution within fish samples from different periods of the year.     

Delayed spawning of perch, Perca fluviatilis L., in acidified lakes

The timing of spawning of perch was examined in four acidified lakes (pH 4.4–4.8) and in one circum-neutral lake (pH 6.3) in southern Finland in spring 1987. In three of the lakes, perch started to spawn soon after the ice melt (4–14 degree days > 5° C) and had spawned by the end of May at about 100 degree days > 5° C. In the two most acidified lakes, fish started to spawn later, at 35 and 60 degree days > 5° C, and had spawned in early June, at about 200 degree days > 5° C. The maturing of gonad products was delayed in both males and females.     

Population structure,growth and fecundity of perch (Perca fluviatilis L.) in an acidified river system in Southern Norway

Population structure, density and reproductive potential of perch (Perca fluviatilis L.) from 4 acidified lakes in a river system in Southern Norway were investigated. The upper 3 lakes were most affected by acidification and the number of perch caught per unit effort indicate three-fold increase in density from the upper Gjerstadvann to the lower Brøbørvann. Low density of perch in the upper lakes is explained by; 1) Abnormal mortality occurring in episodes due to acidification, probably caused by aluminium toxicity at pH = 5.2–5.4. 2). Acid water (pH ≤ 5.0) during spawning and development of eggs and larvae, resulting in recruitment failure. Juvenile mortality of perch may depend on the density of the parental stock. In the 3 upper lakes, the density of adult perch probably was too low to produce significant juvenile mortality, and in these lakes the recruitment probably depended more on the May water quality. Improved water quality increases egg hatching and survival and also benefits zooplankton production, the main food for perch during the first summer. Low population density has reduced competition for food and thus improved growth of perch in the 3 upper lakes compared to the lower lake. The perch in Brøbørvann mature at higher age and have lower individual fecundity than perch in Gjerstadvann, an effect of both slower growth and lower length specific fecundity in Brøbørvann. In Gjerstadvann, the perch therefore have a higher reproductive potential relative to the stock density, and may, when the water quality is good enough, give rise to strong year-classes and more frequent year-class fluctuations than perch in the less acid Brøbørvann.     

Population dynamics of perch, Perca fluviatilis L. in Slapton Ley, Devon

Perch, Percafluviatilis L. were studied in Slapton Ley which is a eutrophic freshwater lagoon in south Devon, England. The perch were caught in traps from February 1970 to June 1971. The traps selected males during the spawning season. The water temperature did not affect the numbers of trapped fish directly, but the sight of perch in the traps appeared to attract others. Sex ratios were found to be equal in the first 2 years of life but older year classes were predominantly female. The population consisted of young individuals. Males were found to mature in their first year and most females matured in their second. The fecundity varied from an average of 1000 eggs in perch n i the 9.75 cm length group to 30,500 eggs in fish in the 27.75 cm group. A few shoals of perch moved throughout the Ley although the majority of fish stayed in the same area. Population estimates showed a range from 10,000 to 95,000 for fish 9.75 cm and above. The large variations in population estimates and survival rates were attributed to the necessity of using traps which had variable catches and to the harmful effects of handling the perch. Chironomids were important in the diet of perch of all sizes. Plankton and Asellus were other important foods, the latter especially during the winter months. Perch 11.5 cm to 13.9 cm selected the widest range of food organisms. Only perch 14.0 cm and above ate fish.     

Swimming activity of perch, Perca fluviatilis L.

The swimming excursions of individual perch, measured automatically, within either cages in Windermere or in a trough on the shore, showed increases at dawn and dusk and in the summer. Similar measurements in troughs in the laboratory showed increased activity following a change from light to dark and vice versa, a pattern that was obliterated by either continuous light or continuous darkness. These results are discussed in relation to water temperature and catches of perch in traps.     

Mortality of perch, Perca fluviatilis L., estimated from the size and abundance of egg strands

Egg strands of perch in Lake Geneva, Switzerland, during the spawning seasons of 1984, 1985 and 1986 were laid by the strong 1982 cohort. The abundance of these strands decreased from 1984 to 1986, whereas their modal size increased. These trends were used to estimate the decreasing abundance of the 1982 cohort and its increasing age. According to these data, total mortality within the 1982 cohort was 99% between the egg stage and 2 years, 78% between 2 and 3 years, 82% between 3 and 4 years.     

Epidermal lesions and fungal infection on the perch, Perca fluviatilis L., in Windermere

An account is given of the histological changes associated with epidermal lesions on the Windermere perch, Perca fluviatilis L., between the months of January and March, 1976. During the later stages of the development of the lesions an apparent succession of fungal colonization was observed. A total of five genera of fungi were identified with Leptomitus lacteus appearing early in the infection and Achlya tending to dominate the more advanced lesions. The initial cause of the lesions has not been identified but the possibility of Argulus damage is discussed.     

The variability in the catches of charr, Salvelinus alpinus L., and perch, Perca fluviatilis L., from multi-mesh gill nets

Multi-mesh gill nets set at Rawlinson's Nab in the south basin of Windermere for 24 months from 1979 to 1981 caught predominantly charr and perch. Nets set parallel to the shore caught significantly fewer fish than those set perpendicular to the shore. Variability in the mean catches of perch increased from winter to summer when the size of the catches also increased. Charr were mostly caught from November until February. Estimates of variance associated with the geometric mean catch of a single net (set perpendicular to the shore) were calculated for the periods winter for the charr and winter, summer, spring and autumn for the perch. These variances were used to calculate 95 and 99% C.L. of the geometric mean. For limits to be below half or twice the geometric mean, 12 nets would have to be used for charr during winter. For perch the number of nets needed would be six in winter, 20 in spring and autumn and 40 in summer. It is concluded that the nets are of little value in assessing changes in stock abundance.     

Mortality and production of 0+ perch, Perca fluviatilis L., in two Scottish lakes

Mortality of 0+ Eurasian perch was measured directly from the decline in catch in a high-speed plankton sampler and described by a negative exponential model. A mean mortality of 0.063 day ¹ (range=0.020–0.089) was calculated; for 0+ juveniles it was 0.021 day ¹. Mean larval production was 0.85–1.30 mg dry weight m⁻² day⁻¹ in Loch Kinord and 0.08–0.12 in Loch Davan. Annual production of 0+ juveniles was 1.97–7.55 kg wet weight ha ⁻¹ at L. Kinord and 1.01 kg at L. Davan. The contribution of 0+ perch, including the egg stages, to total perch production was 88–96%. Availability of food items on transition to exogenous feeding and through the larval period did not limit survival. Cannibalism by adults accounted for most of larval mortality, and predation by pike and adult perch were responsible for the majority of juvenile losses. The population structure of adult perch, for 12 year classes, was stable at L. Kinord, while year classes at L. Davan exhibited fluctuations in abundance and in two sampling years were eliminated in the first summer. Survival in the eleutheroembryonic phase was variable at L. Davan and observed to be low compared with L. Kinord. It is suggested that this was a result of water turbulence on the exposed and shallow spawning areas at L. Davan.     

The responses of a perch, Perca fluviatilis L., population to eutrophication and associated changes in fish fauna in a small lake

A number of parameters were measured in a population of perch whose numbers had declined steeply in a habitat subjected to increasing eutrophication, and these measurements were compared with those taken before the population decline. Contrary to expectation, no adaptive responses were identified. The growth rate of perch up to the age of III had only declined slightly, and there was a marked preponderance of young fish. Relative growth rate was consistent despite the population decline. No dominant year class was apparent. Mean instantaneous mortality rate and annual survival rate were calculated, and the length-weight relationship was analysed. Feeding strategy had not altered since an earlier study. A decline was seen in the percentage of perch maturing at early age. Ripeness coefficients and fecundity estimates were calculated. A previously documented spawning migration was confirmed. The absence of the expected adaptive changes is discussed.     

Retinal development and retinomotor responses in perch, Perca fluviatilis L.

The development of the retina of perch, Perca fluviatilis L., was studied for all developmental stages. The density of cones 100 μm-¹ was found to decrease with age, although their actual numbers increased. All premetamorphosed perch had pure-cone retinae, the rods developing at, or after metamorphosis. Retinomotor responses were found to commence after metamorphosis when the rods developed. Visual acuity, measured as the minimum separable angle (α), was observed to improve exponentially with age, and its value was found to depend more on the focal length of the lens, than on the number of cones in the retina. The cones in the unspecialized part of the retina were predominantly of the twin type and were related to single cones in a ratio of 4 : 1.     

Some aspects of the reproductive biology of perch Perca fluviatilis L. Fecundity, maturation and spawning behaviour

Fecundity of perch estimated from a regression of egg. number on fish length varied from 6711 for a fish of 14.5 cm to 77978 for a female of 34. 5 cm. Other independent variables related to egg number were age, gonad weight and somatic weight. Mean egg diameter varied from 0.94 to 1.62 mm. Males matured in their second year at a length of 6 cm and above while all females spawned at age four at a length of 15–18 cm. A proportion of females at Davan spawned one year earlier than at Kinord and were also slightly smaller on spawning. Faster growth of Davan fish may have encouraged earlier maturation. Spawning behaviour is described from film material.     

Observations on the biology of the perch, Perca fluviatilis, in the River Stour, Dorset

SUMMARY. Opercular bones from 323 perch from the River Stour were used for age and back-calculated growth determinations. Annuli were formed during May at the beginning of the growth period. Growth was minimal from October to April. Female perch grew faster than males, and the growth rates of both sexes were higher than those observed in most other European waters. Spawning occurred during late April and early May; male gonads began development in August and had attained their maximum weight in September, but the ovaries developed gradually from August until April. Immature perch had an annual cycle of condition with a maximum in June-July and a minimum in December-January. The condition of mature males and females was affected by the gonad cycle. The fecundity of Stour perch is expressed by the formula: log egg number = 2.40 log length (mm) - 1.34.
Approximately 25% of males were mature at age I and all were mature at age II, whereas most females did not spawn until age III. Ephemeroptera nymphs and minnow fry constituted the bulk of the diet of 0-group perch; Ephemeroptera nymphs, minnow fry and Corixidae were the most numerous items in I group perch, whereas older perch contained Corixidae and a wider range of fish prey species, although minnows were the most numerous of these.     

Length and weight changes in 0+ perch, Perca fluviatilis L., following fixation in formalin

Significant shrinkage and increase in weight followed fixation of 0+ freshwater Perca fluviatilis in formalin. Conversion values to obtain live values should take account of formalin concentration, fish size and holding time of preserved fish prior to measurement.     

Leucine aminopeptidase activity in the digestive tract of perch, Perca fluviatilis L.

The distribution of the enzyme leucine aminopeptidase (LAP, EC 3.4.1.1) in the digestive tract of perch, Perca fluviatilis L., was investigated histochemically. The enzyme was present in the mucosa of the entire intestine and was absent in the oesophagus, stomach and pyloric sphincter. In the intestine, the enzyme was localized in the supranuclear cytoplasm of the columnar cells and was strongest in the brush border area. Enzyme activity was also present in the lumen of the intestine. The activity of the enzyme in the intestine decreased slightly towards the rectum. In perch, the final digestion of peptides and aminopeptides is both extracellular and intracellular and takes place along the entire length of the intestine.     

Seasonal variations in some blood parameters in perch, Perca fluviatilis L.

Clinical blood tests on fish exposed to contaminants are used extensively both in laboratory and field studies. Seasonal variability is examined in some of the parameters commonly used in health assessments. Hematocrit, hemoglobin concentration and inorganic ion concentration were studied in perch, Perca fluviatilis, from a Baltic brackish water area. Seasonal cycles were demonstrated in hematocrit and in chloride, magnesium and potassium ion concentrations. Other parameters studied reacted irregularly or only slightly to the shift of seasons.     

The predation on Asellus aquaticus (L.) by perch,Perca fluviatilis (L.), in a small forest lake

Asellus aquaticus (L.) was the most important benthic food item for perch, Perca fluviatilis (L.), in a small, extremely humic forest lake in southern Finland. The proportion of A. aquaticus in the diet of perch varied according to the former's availability, which, in turn, depended on its life cycle. Perch 11.0–12.9 cm (total length) most frequently fed on A. aquaticus; smaller and larger perch fed more frequently on crustacean zooplankton and aquatic insect larvae, respectively. The high density of the perch population, the importance of A. aquaticus in the benthos of the study lake and the general high activity level of the prey resulted in a high predation (0.1–1.8% per day). The population of A. aquaticus was also limited by the scarcity of macrophytic vegetation and the small area of oxygenated littoral in the lake.     

The distribution and abundance of young (I +–II +) perch, Perca fluviatilis L., in a deep eutrophic lake, England

Seasonal changes in the vertical and horizontal distribution of young (I +–II +) perch in Rostherne Mere, a deep (max. depth 31.0 m) eutrophic lake are described using sonar. During the summer (June–August), perch were present within the thermocline (9–14° C) between 7 and 10 m. There was no significant difference between samples during this period, nor was there any evidence of shoaling. From September onwards perch moved into deeper waters. By late winter fish had become patchy in their distribution. Total numbers, during the summer, were estimated to be 988 ha ¹ with 95% confidence limits of ±115 (biomass 98.8 kg ha ⁻¹). Densities (no. m⁻³) fell by over 90% after the autumn overturn. The implications for predators are discussed. Acoustic sampling provides a useful, non-destructive method of sampling eutrophic lakes on a routine basis. Information obtained is of ecological, behavioural and physiological interest.