Ontogenetic changes in the bathypelagic distribution of European perch fry Perca fluviatilis monitored by hydroacoustic methods

The behaviour of bathypelagic perch fry (BPF) was monitored during 21 May, 24 June, 8 August and 5 September 1996 along the longitudinal profile of Římov reservoir (Czech Republic), using acoustic methods (SIMRAD EY 500 echosounder, elliptical split-beam transducer, Sonar5 postprocessing software). In May, the BPF layer comprised a mass of solitary perch larvae at an abundance of over 31,000 ind. ha⁻¹. In contrast, in June, the BPF layer consisted almost exclusively of shoaling individuals. The abundance of BPF increased up to 166,000 ind. ha⁻¹. Similary, in August, fish in shoals prevailed in the BPF layer but the abundance dropped to less than 3,000 ind. ha⁻¹. In September, the BPF layer consisted of both individuals and small groups of fish. At this time the abundance of BPF slightly increased to almost 5,000 ind. ha⁻¹. Individual parameters describing the BPF layer, depth of the main layer, abundance of BPF in the main layer and thickness of the whole layer, differed significantly among months. The negligible abundance of potential predators below the thermocline, both in June and in August (exclusively adult perch), suggests that the BPF shoals were more likely to be created as a result of a social need rather than as a defense against predators. During similar surveys carried out prior to (25 April, 5 May, 7 May, 12 May, 15 May) and after this period (3 October, 7 November, 2 December), the BPF layer was not recorded.     

The effect of prey type and density on the foraging efficiency of juvenile perch, (Perca fluviatilis)

The foraging efficiency of juvenile perch (Perca fluviatilis), feeding on two types of prey, was studied in laboratory experiments. Waterfleas (Daphnia magna) and phantom midge larvae (Chaoborus flavicans) were offered in a range of densities, either separately or combined. Perch fed more efficiently on each prey type separately than when both were mixed. Foraging efficiency decreased with an increase of mixed prey density with both prey types present in equal numbers, but also when the proportion of Chaoborus increased. This could be caused by the existence of different hunting techniques, each of which is fully efficient in the presence of one prey type only. In the presence of two prey types, the predator constantly has to switch from one hunting technique to another.     

Intraspecies variation of reproductive strategies in perch (Perca fluviatilis)

The variation of reproductive strategies in different populations of perch and intrapopulation groups differing in the rate of growth have been analyzed. Using a bioenergetic approach, the origin and differences between these groups have been studied. It was shown that bioenergetic mechanisms of regulation of the sizes and weight of the eggs lead to formation of the strategy of forced reproduction in the slow-growing group of perch, unlike the reproductive strategy of the fast-growing group of perch characterized by a later reaching of sexual maturity at a greater relative weight of gonads and spawning of larger eggs, which provides for a longer lifespan of larvae. The great number of age groups in the spawning part of this group compensates for a decrease in reproduction in years with unfavorable conditions.     

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.     

Sperm characteristics in perch Perca fluviatilis L.

Sperm densities in perch Perca fluviatilis males showed a positive correlation with the amount of stripped milt. Sperm flagellum length did not correlate with body mass, but a significant correlation between flagellum length and the total number of sperm produced was found.     

河鲈胚胎及卵黄囊期仔鱼发育

为探究河鲈(Perca fluviatilis)早期生活史和发育生物学,采用体视解剖镜、显微镜仔细观察、测量、描述、绘图的方法,连续观察了6个批次河鲈胚胎及卵黄囊期仔鱼发育状况,进行比较分析。结果显示:(1)在水温8~13℃时,胚胎期约需265h,有效积温2540~2880℃.h;水温11~13℃时,卵黄囊期约需6d,有效积温1750~2120℃.h;(2)辐射状次级卵膜将受精卵连成长带形单层网片状,每个胚胎周围有6个胚胎,排列很有规则。胚胎卵黄囊表面有一个大圆形油球。出膜前期可见眼球色素、胸鳍突起;(3)胚胎出膜的不同步主要是由于出膜前期长短不一和孵化水温较低所致。     

Temperature effects on aerobic scope and cardiac performance of European perch (Perca fluviatilis)

Several recent studies have highlighted how impaired cardiac performance at high temperatures and in hypoxia may compromise the capacity for oxygen transport. Thus, at high temperatures impaired cardiac capacity is proposed to reduce oxygen transport to a degree that lowers aerobic scope and compromises thermal tolerance (the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis). To investigate this hypothesis, we measured aerobic and cardiac performance of a eurythermal freshwater teleost, the European perch (Perca fluviatilis). Rates of oxygen consumption were measured during rest and activity at temperatures between 5 °C and 27 °C, and we evaluated cardiac function by in vivo measurements of heart rate and in vitro studies to determine contractility of myocardial strips. Aerobic scope increased progressively from 5 °C to 21 °C, after which it levelled off. Heart rate showed a similar response. We found little difference between resting and active heart rate at high temperature suggesting that increased cardiac scope during activity is primarily related to changes in stroke volume. To examine the effects of temperature on cardiac capacity, we measured isometric force development in electrically paced myocardial preparations during different combinations of temperature, pacing frequency, oxygenation and adrenergic stimulation. The force-frequency product increased markedly upon adrenergic stimulation at 21 and 27 °C (with higher effects at 21 °C) and the cardiac preparations were highly sensitive to hypoxia. These findings suggest that at (critically) high temperatures, cardiac output may diminish due to a decreased effect of adrenergic stimulation and that this effect may be further exacerbated if the heart becomes hypoxic. Hence cardiac limitations may contribute to the inability to increase aerobic scope at high temperatures in the European perch (Perca fluviatilis).     

Haemogregarina vltavensis n. sp. from perch (Perca fluviatilis) in Czechoslovakia

A new species, Haemogregarina vltavensis n. sp., is described from the blood of perch (Perca fluviatilis) in southwestern Czechoslovakia. Both intra-erythrocytic and free stages interpreted as gametocytes were detected. Only one parasite per erythrocyte was found. It displaces the nucleus and fills most of the volume of the infected host cell. No other developmental stages were discovered.     

Hepatic glucose phosphorylating activities in perch (Perca fluviatilis) after different dietary treatments

Increased activity of hepatic glucose phosphorylation was observed in perch after feeding previously fasted fish. When a pellet diet containing 14% carbohydrate was given, most of the increased activity had a low affinity towards glucose (S0.5 = 19.5 mM) and resembled the mammalian glucokinase (Hexokinase IV or D) and the glucokinase-like activity previously observed in salmon liver. In addition, increased activity of a hexokinase with high affinity towards glucose (Km = 0.50 mM) was observed with the pellet diet. An increase in the activity of this hexokinase alone was observed when the fish were fed with filet of cod containing less than 0.2% carbohydrate. Perch with a very high hepatic glucokinase-like activity after eating the pellet diet had high activities of pyruvate kinase and glucose-6-phosphate dehydrogenase, indicating a high capacity of glycolysis and carbohydrate utilization. Simultaneously, the activity of glycogen phosphorylase was strongly reduced while the activity of fructose-1,6-bisphosphatase was not significantly changed. These observations were made with perch captured in the spawning season and brought to the laboratory. Assays of glucose phosphorylation in livers of perch eating the natural diet (insects) in the lake showed no glucokinase-like activity.     

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.     

Predation by underyearling perch (Perca fluviatilis) on a Daphnia galeata population in a short-term enclosure experiment

1. The predation impact of underyearling perch (20 mm total length) on the dynamics of Daphnia galeata was studied in three 6.5-m³ enclosures during a 17-day experiment in June 1995. These data were compared with zooplankton succession in three fish-free control enclosures and in the pelagic zone of Bautzen reservoir, Germany. 2. Due to individual growth during the experiment, fish biomass in the enclosures increased from 210 mg wet body mass (w.b.m.) m^–3 to 830 mg w.b.m. m^–3, equivalent to an increase from 20 kg ha^–1 to 75 kg ha^–1. 3. In the enclosures with fish, biomass of daphnids decreased steadily to values below 1 mg wet weight (w.w.) l^–1 within 17 days, whereas in the fish-free controls and in Bautzen reservoir the Daphnia biomass fluctuated around 8 mg w.w. l^–1. Other zooplankton species exhibited little or no change. Approximately 60 kg ha^–1 was calculated as the critical underyearling perch biomass which may induce a drastic decline of the Daphnia galeata population in Bautzen reservoir. Comparison with values from other lakes is difficult due to differences in water depths and Daphnia biomasses. 4. Mean individual biomass of daphnids, egg ratio and proportion of adult daphnids were significantly lower in the enclosures with fish compared with the control enclosures at the end of the experiment. This may be explained partly by preferential predation of the large, egg-carrying daphnids by fish. However, no difference was found in clutch size and size at first reproduction, possibly due to the short duration of the experiment. 5. It must be assumed that the ‘summer depression’ of daphnids observed in many waters is not the exclusive effect of direct reduction of daphnids by fish predation. Even the high biomass of underyearling perch stocked in the enclosures did not completely account for Daphnia mortality. Instead, the selective loss of large size classes, combined with low food resources and reduced reproduction rates, may induce the marked declines in daphnids.     

The influence of water pH on the perivitelline fluid of perch (Perca fluviatilis) eggs

The diameter, trans-chorion potential difference and perivitelline-fluid pH of the eggs of perch (Perca fluviatilis) have been measured in a range of water pH (8-4.5). The water used was relatively nutrient rich. Eggs transferred from pH 8 to pH 4.5 shrink; probably as a result of loss of water from perivitelline fluid. Trans-chorion potential differences are close to zero over the range of pH. Mean perivitelline-fluid pH is higher than external water pH at pH 6.7 and above. Below pH 6.7, mean perivitelline-fluid pH is approximately the same as external water pH. The results suggest a non-Donnan distribution of hydrogen ions. The results are compared with data on salmonid eggs in nutrient-poor waters.     

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.     

Proposed standard weight (Ws) equation for European perch (Perca fluviatilis Linnaeus, 1758)

Relative weight (W_r) is an important and commonly used condition index that provides a measure of the well‐being of a fish population by comparing the actual weight of a specimen with the ideal weight of a specimen of the same species and of the same length in good physiological condition, i.e. the standard weight (W_s). Two methods of calculating the standard weight are proposed in the literature: the RLP method and the EmP method. The aim of this study was to develop a standard weight equation for European perch by means of both methods, using length–weight data from 64 913 fish from 18 countries (across Europe and Oceania). The resulting equations were: log₁₀ (W_s) = ?3.1483 + 1.2663 log₁₀ (TL) + 0.4291 [log₁₀ (TL)]² for the EmP method and log₁₀ (W_s) = ?5.3493 + 3.2152 log₁₀ (TL) for the RLP method. The applicable length‐range of the two W_s equations was restricted to 80–460 mm. A further research aim was to compare the performances of RLP and EmP. The resulting quadratic EmP W_s equation did not exhibit length‐related biases, which suggests that it can be used to compute relative weight for European perch.     

Competition for minerals between Acanthocephalus lucii and its definitive host perch (Perca fluviatilis)

Concentrations of various essential and toxic elements (Ba, Ca, Co, Cu, Fe, Mg, Mn, Sr, Zn and Al, Ag, Cd, Cr, Ni, Pb, Tl) were analysed by inductively coupled plasma mass spectrometry in the acanthocephalan Acanthocephalus lucii and in different tissues of its host Perca fluviatilis. Nearly all the elements were found in significantly higher concentrations in the acanthocephalan than in the host tissues. Spearman correlation analysis revealed several strong inter-element associations within the organs of perch and within the parasites. Furthermore, statistical analysis revealed different competitive interactions. The concentrations of several essential elements (Ba, Ca, Fe, Mn, Sr and Zn) within the parasites decreased with an increasing number or weight of worms inside the intestine of the host. Additionally, the levels of some elements in the perch liver were negatively correlated with the weight of A. lucii in the intestine. Thus, it emerged that not only is there competition for essential elements between acanthocephalans inside the gut but there is also competition for these elements between the host and its parasites.     

Warming alters the body shape of European perch Perca fluviatilis

The consequences of elevated temperature on body shape were investigated by comparing European perch Perca fluviatilis from the Forsmark area of the Baltic Sea to P. fluviatilis from a nearby Biotest enclosure. The Biotest is a man‐made enclosure within the Baltic Sea that has received warm water from a nuclear power plant since 1980, resulting in temperatures that are elevated 5–10° C relative to the surrounding Baltic Sea. Sampled fish ranged from young‐of‐the‐year to 14 years. Geometric morphometrics and multivariate statistical analysis revealed significant morphological differences between individuals of P. fluviatilis from these two habitats. Most importantly, relative shape changed with size, with small individuals of P. fluviatilis from Biotest being characterized by a deeper body shape and a larger caudal peduncle than the smaller Baltic individuals. In large specimens, smaller differences were found with Biotest individuals being more slender than Baltic individuals. These results show that, in order to have a full understanding of the biological effects of elevated temperatures, studies that cover the entire size range of organisms will be important. Apart from the direct influence of temperature on growth rate and body shape, other ecological factors affected by temperature are discussed as possible contributors to the observed differences between the two populations.     

Effects of temperature on allocation of metabolic energy in perch (Perca fluviatilis) fed submaximal rations

Growth and long-term trends of oxygen consumption were monitored at 15 and 20° C in spontaneously swimming juvenile perch fed a fixed daily submaximal ration. The average rate as well as the efficiency of assimilation were the same at the two temperatures but a much higher proportion of food energy was allocated to activity and maintenance, and a correspondingly lower proportion to growth, at 20 than at 15° C. By computing average specific rates of oxygen consumption separately for all light and dark periods, it was found that at 20, but not at 15° C, the' scope for spontaneous activity' of two consecutive (dark and light) phases of a diurnal cycle was indirectly proportional to the average rate of oxygen consumption in the dark phase. This indicates that at 20° C the perch displayed partial compensation for a high metabolic rate in the dark by reducing swimming activity in the following light phase. However, the overall effect of this behaviour was probably too small to make a noticeable impact on the low conversion efficiency in the juvenile perch at 20 as compared to 15° C.     

Responses of Acilius sulcatus (Coleoptera: Dytiscidae) to chemical cues from perch (Perca fluviatilis)

In this study we tested the hypothesis that the presence of chemical stimuli from a hungry predator would initiate anti-predator responses, while stimuli from a satiated predator would not. We used chemical stimuli released from starved perch (Perca fluviatilis) and from satiated perch (predator). As prey we used adult Acilius sulcatus (Coleoptera: Dytiscidae). The reaction of the beetles to different predator conditions was tested during daytime. We also tested the reaction to starved perch during the night. A. sulcatus activity decreased when it was exposed to stimuli released from starved perch during daytime when visibility was poor, due to the presence of artificial vegetation. There was, however, no reaction to satiated perch under the same experimental conditions. These results indicate that A. sulcatus can discriminate between chemical cues from hungry and satiated fish predators. When visibility was good and the concentration of chemical cues was constant, the beetles did not react to starved perch in the daytime, but their activity decreased at night in response to stimuli released from starved perch. Visual as well as chemical cues seem to be important for detecting a potential predator. When visibility is good, beetles seem to rely on visual stimuli, while in darkness they seem to use chemical stimuli to detect the presence of predators. Received: 4 October 1996 / Accepted: 7 February 1997     

Enhancement of the phototactic reaction in Daphnia hyalina by a chemical mediated by juvenile perch (Perca fluviatilis)

Experiments with Daphnia hyalina demonstrated that the phototacticreaction to changes in light intensity is strongly enhancedin the presence of a chemical substance mediated by juvenileperch. In constant light intensity, the daphnids were foundclose to the bottom of the experimental aquarium. The phenomenonmay result in a diel vertical migration. This would decreasepredation pressure near the surface.     

Effects of passive integrated transponder tags on short-term feeding patterns in European perch (Perca fluviatilis)

We tested the feeding behaviour of small European perch (Perca fluviatilis) in a laboratory study during the first 24 h after handling and 23 mm passive integrated transponder (PIT) tag implantation. Feeding commenced almost immediately following tagging and overall feeding patterns were unaffected by tagging. However, untagged perch had more feeding events than PIT-tagged individuals. This discrepancy could be attributed to post-tagging effects or/and reduced room for food due to the presence of the tag in the body cavity.