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.     

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.     

Energetics and metabolic correlates of starvation in juvenile perch (Perca fluviatilis)

Long-term measurements of the diurnal pattern of oxygen consumption were conducted in fasting juvenile perch at 15 and at 20° C. In addition, dry body mass, protein and glycogen concentrations and the activity of two key enzymes of energy metabolism, phosphofructokinase and glutamate pyruvate transaminase, were monitored during the period of food deprivation. The average rate of oxygen consumption decreased during the starvation period, but the regular diurnal pattern of low rates in the dark and high rates in the light was upset by a break around days 7 to 8 at both temperatures. This break coincided with the exhaustion of the glycogen reserves in the muscles and in the liver, indicating that switching to a new energetic fuel was accompanied by a change in the pattern of swimming activity. Choice of the major energy source after exhaustion of the carbohydrate store was substantially influenced by water temperature. A negative correlation was found between the scope for spontaneous activity and the specific rate of oxygen consumption in the dark phase suggesting that the resting rate of metabolism responded more strongly to food deprivation than the rate of spontaneous activity in the light phase.     

Seasonal variation in the catching power of traps used for perch, Perca fluviatilis L.

The number of perch caught weekly in traps set in Slapton Ley, Devon has been considered. Five traps were laid in each of six regions during 1970 and 1971. The numbers caught in each region were averaged for eight lifts during 8 weeks and the logarithms of these numbers calculated. The figures obtained showed marked seasonal trends in the catch of the traps and these trends were consistent when both years were compared. If single traps were considered there was marked variability at one time which was attributed to differences in habitat. However, the combined data from each region did give a good comparison of the density of perch between regions.     

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.     

Exceptionally big individual perch (Perca fluviatilis L.) and their growth

In Lake Windermere (U.K.) where there was a dense, slow-growing population of perch ( Perca fluviatilis L.) which had an l _x of about 180 mm, there co-existed a few individuals with an l _x of 463 mm. Data from 137 of these big perch, mostly caught in gillnets fishing for Esox lucius L., were examined. Their early growth was identical to that of normal perch, but, at an age, varying between individuals, from 1 to 8 and averaging 4 years, their growth accelerated for about 4 years and then followed a von Bertalanffy model with an l _x of 463 mm. They thus had a 'double' growth-curve that is revealed only if individual growth is examined. Acceleration tended to occur in certain calendar years and was correlated with strong year-classes of young perch. Growth was greater in years with warm summer water temperatures. There were no changes in the growth of big perch, after they had achieved 290 mm, during a period of great changes in the population density and an increase in the growth of normal perch < 290 mm. No more big perch were caught in Windermere between 1967 and 1990. Net selection, length-weight relationships, seasonal cycle in gonad weight, and opercular-body length relationship were the same as those of normal perch. The few available data suggest that big perch were piscivorous, feeding largely on small perch. The distribution of sites in the lake where big perch were caught is contagious, catches follow the negative binomial; but within fishings that caught big perch at the same site and time, catches were more evenly distributed than random. It is postulated that most adults would have accelerated their growth if they had sustained piscivory. Similar big perch have been found in other lakes.     

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.     

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.     

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.     

Local growth differences in perch (Perca fluviatilis L.) in a Baltic archipelago

Data on the chemical composition of the hard water rivers Rhine and Rhone, published elsewhere, are stored in a new data bank, RRQUE. In this paper the seasonal variation in pH and concentrations of calcium, bicarbonate and sulphate at 7 stations in the Rhine and 7 in the Rhone are described. The concentrations of calcium, bicarbonate and sulphate show important increases with increasing distance from the source. In both rivers acidification gradually occurs downstream and is thought to be caused by the decomposition of disposed organic matter. It is shown that the normal seasonal patterns of these 4 chemical variables are negated by anthropogenic effects.     

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.     

The variability in numbers of perch Perca fluviatilis L. caught in traps

The variability in the catch of perch traps set in Windermere over the period 1955–70 has been analysed. Altogether 2690 catches in four series have been treated by analyses of variance after a logarithmic transformation. A representative value of the between traps variance from all sources of variation has been used to estimate the reliability of the mean catches based on different numbers of traps. It is shown that many traps are needed to obtain consistent results.     

On the early growth of 0+ perch, Perca fluviatilis, in Windermere

SUMMARY. The growth in length and weight (wet and dry) of 0+ perch Perca fluviatilis during their first summer of life in Windermere, has been investigated. Two major stanzas, occurring during and after metamorphosis, characterize the growth of 0+ perch in Windermere. The change from one stanza to another takes place between six and eight weeks after hatching. The exponential rate of growth in length was 0.26 and 0.27 mm mm⁻¹ week⁻¹ for the first stanzas of 1975 and 1976, respectively, and decreased to about 0.08 and 0.07 mm mm⁻¹ week⁻¹ for the second stanzas of the same years. Similarly, the growth in both wet and dry weights decreased from the first to the second stanza. Growth of 0+ perch was found to be logistic, and could not be described by the von Bertalanffy growth curve. The relationship between weight and length was allometric and the power values for length were, for wet weight: 4.154 (in 1975) and 4.033 (in 1976) for the first stanza and 2.400 (in 1975) and 2.734 (in 1976) for the second stanza; for dry weight: 3.988 (1975) and 3.971 (1976) for the first stanza and 3.066 (1975) and 2.651 (1976) for the second stanza. Half of the total growth was completed in 47% (1975) and 40% (1976) of the total growth period to the end of the summer.     

Differences in growth of perch (Perca fluviatilis L.) in two small forest lakes

Growth patterns and food composition of perch, Perca fluviatilis L., was studied in two small forest lake populations in southern Finland. Size and morphometry of the lakes and physical and chemical properties of water are similar. There is a clear difference in the growth rates of perch between the two lakes. The difference in growth is highly significant in all age groups. In the first lake there is a perch population of 2 000 (1750 ind · ha^–1) adult fishes. In the second lake there is a small population of pike, that keeps the perch population down: 200 adult perch (530 ind · ha^-1). The main food items of perch are crustacean zooplankton, Asellus aquaticus L. and Trichoptera larvae in the first lake and zooplankton, Odonata larvae, Ephemeroptera larvae and Heteroptera in the second.It is concluded that the main reason for the growth difference of studied perch populations is the different population density. There are also differences in species composition of bottom fauna of the lakes, maybe owing to the floating Sphagnum peat moss vegetation in the second lake. This can also affect the growth difference between the two populations of perch.     

Effect of body mass and water temperature on the standard metabolic rate of juvenile yellow perch, Perca flavescens (Mitchill)

Fish respiration rates that are presumed to represent standard metabolic rates (SMR) may sometimes include an unspecified energy expenditure associated with activity and digestion. This situation may introduce a bias in bioenergetics models because standard metabolism, digestion, and activity may not be affected by the same environmental conditions. The aim of this study was to (1) develop a SMR model for juvenile yellow perch, Perca flavescens (Mitchill), that represent the minimum energy expenditure required to maintain life and (2) compare the results of this study with published perch metabolic rates and bioenergetics models. SMR was estimated for yellow perch over a range of body␣mass (4.4–24.7 g) and water temperature (12–20°C). The intercept of the relationship between fish respiration and swimming velocity obtained during forced swimming experiments was used to determine SMR. SMR estimated by the present study were comparable to values presented by two published studies on Eurasian perch, Perca fluviatilis L. However, estimated SMR were 4.1–20.9 times lower than values of a third respirometry study and predictions of bioenergetics models for perch. The present study suggests that published SMR models may sometimes include a significant fraction of energy expenditures (39.2–75.9%) associated with digestion and activity. This may complicate the implementation and the interpretation of fish bioenergetics models. The present study indicates that the intercept of respiration-velocity relationships and long-term respiration rates during starvation experiments may provide similar and reliable SMR values.     

A note on the age composition, growth rate and food of perch Perca fluviatilis (L.) in four eutrophic lakes, England

The perch populations of all lakes sampled are characterised by high growth rates (l± 320–410 mm) and year-class instability. The concurrence of four year-classes (1970,1973,1975and 1976) in three of the lakes is good evidence for climatic control of recruitment. Poor recruitment in Rostherne Mere during 1973 is attributed to the effects of cannibalism. An increase in the growth rate of young fish (0+) in all lakes during 1975 and 1976 is noted. The relatively poor growth of perch in Rostherne Mere is a consequence of the low specific growth rate there during the first year of life. An outbreak of the 'perch-disease' killed most of the adult perch present in 1975 in Rostherne Mere.     

Non-specific carboxylic esterase activity in the digestive tract of the perch, Perca fluviatilis L.

The distribution of non-specific carboxylic esterases (Ec 3.1.1) in the digestive tract of perch, Perca fluviatilis L., was investigated histochemically using 1-naphthyl acetate as the substrate. Strong enzymatic activity was present in the gastric glands and surface cells of the stomach, intestinal mucosa of the pyloric caeca, upper and middle intestine, pancreas (exocrine cells) and liver. The enzymatic activity in the lower intestine and rectum was weak. The activity was not demonstrated in the oesophagus or pyloric sphincter. In the intestine, the activity was localized in the columnar cells especially in the supranuclear cytoplasm. The enzymatic activity demonstrated in the digestive tract of perch using 1 -naphthyl acetate represents combined esterolytic and lipoproteolytic activity.