Consumption of crucian carp (Carassius carassius L., 1758) by restocked pike (Esox lucius L., 1758) in a lake with frequent winter hypoxia

To assess the effects of stocked pike (Esox lucius L.) on crucian carp (Carassius carassius L.) biomasses, the annual consumption of pike was estimated and compared with removal fishery catches. The studied lake, Lake Savijärvi, is a small (40 ha), shallow and eutrophicated lake in southern Finland with frequent algal blooms during summers and fish kills during winters. Until the 1980s, the fish fauna consisted of pike, perch (Perca fluviatilis L.), roach [Rutilus rutilus (L.)], crucian carp, and tench (Tinca tinca L.). Since 2003, when crucian carp were abundant in the extreme and with only a few roach and tench individuals, the lake has been biomanipulated by removal seining. To enhance the effects of seining, piscivorous pike were restocked in the spring of 2008. During the 3‐year study, the catch of crucian carp decreased from 243 to 136 kg while the catch of pike increased from 0.1 to 5.7 kg per seining hectare due to their spawning in the lake as of 2009. The total crucian carp consumption by captured pike was 588 kg during the 2008–2010 study period. When applying the number of pike estimated with the mark‐recapture method, consumption estimate increased to 917 kg, or 22.9 kg per lake hectare in 2010. Thus, pike consumption of crucian carp was about 17% of the removal catch in 2010.     

Body morphology of crucian carp Carassius carassius in lakes with or without piscivorous fish

Crucian carp Carassius carassius was sampled during 1993 and 1994 in 21 lakes and ponds in east Norway In 10 of these lakes and ponds no piscivorous fish species was present, and in the remaining 11 lakes and ponds predators such as perch Perca fluvtalilis. pike Esox lucius, and trout Salmo trutta were common In general, crucian carp was larger in the lakes with predators than in those without predators The relative body depth (body height/body length) of crucian carp was significantly deeper in populations sympatric with predators (mean 0 358), compared to allopatric populations (mean 0 286) The variation in relative body depth was larger among the sympatric populations than among the allopatric populations The observed difference in relative body depth may be due to 1) predator induced changes m body morphology, 2) increased growth rates in lakes containing predator due to reduced intraspecific competition, and 3) size-selective predation     

Effect of temperature on proteinase activites of enteral microbiota and intestinal mucosa of fish of different ecological groups

Effect of temperature on proteinases activities of enteral microbiota and of intestinal mucosa was studied in five fish species (roach Rutilus rutilus, crucian carp Carassius carassius, common perch Perca fluviatilis, pike-perch Zander lucioperca, and pike Esox lucius) belonging by the nutrition type to different ecological groups. Essential differences of temperature characteristics of proteinases of intestinal mucosa and of enteral microbiota are revealed in fish belonging to different ecological groups. The character of the t-function of proteinases of intestinal mucosa and enteral microbiota for casein and hemoglobin as a rule is different. The values of the apparent E _act proteinases of intestinal mucosa for casein in most cases are higher than those of enteral microbiota, while those for hemoglobin, on the contrary, are lower. The lowest values of relative proteinase activities for casein in the zone of low temperatures (38 and 45.3% of the maximal activity) and the E_act value (less than 2.0 kcal/mol) are found at study of proteinases of enteral microbiota in common perch and crucian carp. The latter indicates a significant adaptability of the enteral microbiota proteinases of common perch and crucian carp to functioning at low temperatures.     

Predator recognition and defence strategies in crucian carp, Carassius carassius

Crucian carp from populations that lack piscivores are extremely vulnerable to predation. However, in the presence of piscivores these fish develop an inducible morphological defence, a deep body. This switch from a vulnerable, shallow-bodied morph to a morphologically defended morph makes this species very suitable for investigations of anti-predator strategies, and trade-offs between morphological and behavioural defences. To address these questions, we performed eight different experiments. We found that crucian carp exhibited fright responses to chemical cues from unfamiliar predators (northern pike, perch) when these were fed prey that contained alarm substance (for northern pike: crucian carp, roach; for perch: crucian carp). Cues from small pike that were fed prey that lacked alarm substance (swordtails) caused no significant fright response whereas cues from larger pike with the same diet did. Perch on a chironomid diet elicited weaker but significant fright responses. Starved predators caused as strong fright reactions as recently fed ones did, whereas no response was exhibited towards nonpredatory fish (roach, crucian carp). Crucian carp were able to detect the presence of pike after cues had been diluted to an equivalent of 21 000 l, and larger predators elicited stronger fright responses. Prior experience of predators decreased fright responses. In particular, individuals from populations that coexisted with northern pike responded less to chemical cues from northern pike than individuals without prior experience did. Thus, crucian carp may use both alarm-substance related and predator-related cues to identify predators. Further, they were able to discriminate between large and small predators. Finally, individuals from populations that coexist with predators exhibit less pronounced fright responses. These fish have an induced morphological defence, a deep body, which most likely decreases the need for strong antipredator behaviour.     

Changes in the fish community and water quality during seven years of stocking piscivorous fish in a shallow lake

SUMMARY 1. Piscivores (annual stocking of 1000 individuals ha^?1 of 0+ pike and a single stocking of 30 kg ha^?1 of large 20–30 cm perch) were stocked in seven consecutive years in a shallow eutrophic lake in Denmark. The stocking programme aimed at changing food‐web structure by reducing zooplanktivorous and benthivorous fish, with resultant effects on lower trophic levels and ultimately water quality. 2. The fish community and water quality parameters (Secchi depth, concentrations of total phosphorus, chlorophyll a and suspended solids) were monitored between 1996 and 2000 and relationships were evaluated between predatory fish and potential prey and between zooplanktivorous or benthivorous fish and water quality parameters. In addition, potential consumption of piscivorous fishes was calculated. 3. The density of fish feeding on larger zooplankton or benthos (roach >15 cm, crucian carp >15 cm) declined distinctly during the study period. This effect was attributed to predation by large (>50 cm) pike. Based on scale readings, we cautiously suggest that the stocking of 0+ pike boosted the adult pike population to produce an unexpected impact in later years. Conversely, no direct impact of stocked 0+ pike was detected on 0+ roach. 4. A major decline in the recruitment strength of 0+ roach was observed in 2000. A combination of (i) the indirect effect of large pike preying on adult roach, with negative effect on roach reproduction and (ii) the direct predation effect of 0+ pike and/or 1+ and 2+ perch recruited in the lake, provides the most likely explanation of this phenomenon. 5. A marked increase in Secchi depth in 2000 and declining trends in suspended solids, chlorophyll‐a and total phosphorus concentrations were observed. These changes may also be attributable to changes in the fish community, although the relationships were not straightforward. 6. This 7‐year study indicates that piscivorous fish may be a significant structuring force in shallow eutrophic lakes, suggesting that stocking piscivores can increase predation pressure on cyprinids. However, the general lack of impact of 0+ pike points to the need of refining current stocking practices in several countries across Europe.     

Individual specialization and trophic adaptability of northern pike (Esox lucius): an isotope and dietary analysis

Northern pike (Esox lucius) are often considered to be specialist piscivores, but under some circumstances will continue to eat invertebrates as adults. To examine effects of fish assemblage composition on the trophic ecology of pike, we combined stable isotope analysis (SIA) of carbon and nitrogen and stomach content analysis (SCA) on pike from five lakes in northern Alberta, three of which contain only pike (“pike-only”) and two that also contain yellow perch (Perca flavescens) or white sucker (Catostomus commersoni) (“pike-other”). Fish were more important as prey and empty stomachs, which often characterize piscivores, were significantly more frequent in pike-other than in pike-only lakes. However, even though invertebrates were more important for pike in pike-only lakes, SIA and SCA indicated that invertebrates were also an important component of pike diets in pike-other lakes. SIA and SCA also revealed considerable intrapopulation variation in trophic ecology, with individuals in some populations differing by as much as two trophic levels. Comparisons of stomach contents and isotope signatures of the same fish suggested that within these variable populations, specialization on invertebrates or fish was a long-term trait of some individuals. SIA indicated that trophic position increased and diets shifted to a greater importance of littoral prey as pike grew in pike-only lakes, but not in lakes with other fish present. Trophic adaptability in northern pike is expressed at both the population level, where the trophic ecology is sensitive to differences in prey regimes, and at the organismal level, in the form of intrapopulation variation and individual specialization. Received: 1 July 1998 / Accepted: 3 February 1999     

The population dynamics of pike,Esox lucius,and perch,Perca fluviatilis,in a simple predator-prey system

Synopsis The population dynamics and predator-prey relationship of pike, Esox lucius, and perch, Perca fluviatilis, were examined in simple fish communities in two adjacent shallow lakes, Lochs Kinord and Davan, Deeside, Scotland. Few perch survive to age 3 but Z is low for fish > 3 years and perch live up to 17 years. Population fecundity remained relatively high and constant in perch because of the multi-age spawning stock and the presence of older more fecund perch. Growth rates of perch in both lochs are relatively high as a consequence of low stock abundance. The N, B, and P of adult perch were unusually low. The age range of pike, and N, B, P, and growth were in the range of values reported elsewhere. There was little variation in the strength of pike year classes and the importance of cannibalism and low occurrence of alternative prey in the lochs suggest that the populations were self-regulating. Cannibalism by adults was responsible for most of mortality in perch larvae, and predation by pike and adult perch was responsible for the majority of juvenile losses. This conclusion is supported by the high biomass ratios of pike:juvenile perch of 1.0–30.8. While the number of adult fish was almost equal, the biomass of adult pike was 2–3 × that of perch in Kinord and 6 × in Davan. In L. Kinord, where year class strength was stable, high predation pressure from perch and pike reduced perch abundance rather than eliminated year classes. Perch year classes fluctuated in abundance in L. Davan and were eliminated in the first summer in two sampling years. The pike, and particularly the perch populations, have features characteristic of fish communities in unperturbed ecosystems: namely, a wide range of age classes, stability in biomass with variation dampened by longevity, and low production.     

Development of fish communities in lakes after biomanipulation

Biomanipulation measures in the Netherlands are usually a combination of a drastic fish stock reduction and an introduction of pike fingerlings. In three small shallow lakes (Noorddiep, Bleiswijkse Zoom and Zwemlust) these measures resulted in a clear water state and the development of macrophytes. After the measures the fish community developed differently because of the new physical and biological conditions. Results of lake Noorddiep and lake Bleiswijkse Zoom showed that the fish community became more divers. Bream and carp became less dominant and were partly replaced by roach and perch. The importance of the main predator pike-perch was strongly reduced and replaced by pike and perch. The share of piscivorous fish in the total fish stock increased at all sites. The recruitment of young-of-the-year was similar or even higher in the clear overgrown areas than in the turbid water before the measures, but the recruitment of young-of-the-year to older fish differed between the species. Predation by pike and perch could not control the young-of-the-year cyprinids, but their predation may have contributed to the shift from bream to roach, because of selective predation on bream in the open water, while roach was hiding in the vegetation. The macrophytes provide new refugia and feeding conditions that favour roach and perch, but offer relatively poor survival conditions for bream and carp.     

Predation risk and feeding patterns of crucian carp

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carp Carassius carassius were compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perch Perca fluviatilis . Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presence v . absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.     

Effect of temperature on proteinase activities of enteral microbiota and intestinal mucosa of fish of different ecological group

Effect of temperature on proteinases activities of enteral microbiota and of intestinal mucosa was studied in five fish species (roach Rutilus rutilus, crucian carp Carassius carassius, common perch Perca fluviatilis, pike-perch Zander lucioperca, and pike Esox lucius) belonging by the nutrition type to different ecological groups. Essential differences of temperature characteristics of proteinases of intestinal mucosa and of enteral microbiota are revealed in fish belonging by the nutrition type to different ecologic groups. The character of the t0-function of proteinases of intestinal mucosa and enteral microbiota by casein and hemoglobin as a rule is different. The highest values of relative proteinases activities for casein in the zone of low temperatures (38 and 45.3 % of the maximal activity) are found at study of proteinases of enteral microbiota in common perch and crucian carp. The latter indicates a significant adaptability of the enteral microbiota proteinases of common perch and crucial carp to functioning at low temperatures.     

The distribution and growth of coarse fish in gravel-pit lakes in south-east England

SUMMARY. Age and growth rates of the coarse fish of thirty-nine gravel-pit lakes in south-east England are compared. Species composition was very variable, the commonest species being roach ( Rutilus rutilus ), bream ( Abramis brama ), tench ( Tinca tinca ), perch ( Perca fluviatilis ) and pike ( Esox lucius ). Two main kinds of fish community were identifiable from the survey: (1) those consisting of a mixture of cyprinids, usually roach and bream; and (2) those in which cyprinids were rare or absent and the fish community was composed of perch and pike. The majority of the lakes fell into the first category. Comparison of growth curves derived by back-calculation showed that, in all species, variation occurred from lake to lake and from year to year. The majority of gravel-pit lake fishes had 'medium' growth rates when compared with published data by other workers on different waters. Seasonal growth of roach infected with plerocercoids of Ligula intestinalis was observed at monthly intervals. Annulus formation on the scales of these fish occurred at the onset of growth in May. The heavy Ligula burden in 89% of these fish had not caused the formation of any additional or false rings.     

The Diel Activity of Crucian Carp, Carassius Carassius, in Relation to Chemical Cues from Predators

Chemical cues from piscivorous fish and prey alarm substances often cause rapid fright responses in prey. However little is known of how piscivore-related chemical cues affect prey behaviour over periods longer than a few hours. Here we have investigated how chemical cues from piscivorous northern pike, Esox lucius, affect habitat choice and diel activity of crucian carp, Carassius carassius, over an extended period 11 days. At the beginning of the experiment control fish were nocturnal while fish in the pike cue treatment were aperiodic. After 11 days, control fish had become more strongly nocturnal and displayed two activity peaks during early and late night whereas fish in the pike cue treatment were still aperiodic with no activity peaks. Habitat choice was aperiodic in both treatments throughout the experiment. In both treatments, more fish were found in the vegetation zone than in the open habitat. This was most pronounced when pike cues were present. These results demonstrate that short-term anti-predator responses to chemical cues from predators can translate into long-term adjustments of diel periodicity. Further, the results did not support the idea that crucian carp should switch to nocturnal activity in response to visually hunting predators. Control fish were nocturnal and chemical cues from pike did not make this pattern more pronounced.     

Factors influencing changes in mercury concentrations in lake water and yellow perch (<Emphasis Type="Italic">Perca flavescens</Emphasis>) in Adirondack lakes

Over the past 20+ years, fish with elevated concentrations of mercury (Hg) have been observed in remote lake districts, including the Adirondack region of New York. Across eastern North America studies have also reported a negative correlation between fish Hg concentration and lake pH. Recent controls in emissions of sulfur dioxide (SO₂) have resulted in some improvement in the acid–base status of acid-impacted surface waters including Adirondack lakes. In addition, there has been an apparent decrease in atmospheric Hg deposition. A synoptic survey of 25 lakes in the Adirondacks was conducted in 1992–1993 to analyze spatial patterns of Hg in the water column and yellow perch (Perca flavescens). The same cluster of 25 lakes was resurveyed in 2005–2006 to evaluate if changes in lake concentrations of Hg species or fish Hg have occurred. We observed a varied response of changes in water chemistry and fish Hg concentrations. In twelve of the resurveyed lakes the yellow perch had lower Hg concentrations, six lakes had yellow perch with higher Hg concentrations, and in seven lakes yellow perch Hg concentrations did not change significantly (α = 0.05). Four variables appear to influence the change in yellow perch Hg concentrations in the Adirondacks: watershed area, elevation, change in pH, and change in fish body condition. We hypothesize that as the acidity in lakes is attenuated, the lakes may become more productive and/or water quality conditions less stressful to fish leading to increasing fish body condition. As fish body condition improves, fish exhibit “growth dilution” of tissue contaminants leading to lower fish Hg concentrations.     

Relationships between mercury in lake water,water colour and mercury in fish

The relationship between mercury content in fish (pike and perch), the different fractions of mercury in lake water and water color was investigated in 76, mainly oligotrophic lakes distributed over a large part of Sweden. The lakes were classified in terms of drainage area characteristics, lake morphometry and water chemistry. The dominant fraction of mercury in lake water was RIHg (fraction reducible to elemental mercury by NaBH₄). RIHg and water color were strongly positively correlated. Water color (determined by the comparative method using colored disks) was used as a surrogate for the amount of humic matter in the water. Thus, humic matter appears to be acting as an important carrier of mercury. A positive relationship between mercury content in fish and water color was found only in deep lakes (average depth > 5 m). It is suggested that the bioavailability of mercury attached to humic matter increases due to anoxic conditions, common in the hypolimnion of deep lakes.     

Chernobyl-derived radiocaesium in fish as dependent on water quality and lake morphometry

¹³⁷Cs concentrations in perch Perca fluviatilis , pike Esox lucius and roach Rutilus rutilus obtained from lakes of different size and water quality in an area which received about 10–67 kBq m⁻²¹³⁷Cs, were compared with environmental data. Radiocaesium concentrations were highest in pike, and were about two to three times higher in the pike and perch than in the roach. The largest perch had about four times more ¹³⁷Cs than the smallest ones, but the activities in the pike and roach were independent of fish size. All of the water quality parameters examined correlated with ¹³⁷Cs concentrations in the fish, but the concentrations of ¹³⁷Cs in the bottom sediment did not. ^l37Cs fallout and water retention time in lakes showed a positive correlation with fish ¹³⁷Cs, while the size of the catchment area, phosphorus content of the water, water colour, pH and electrical conductivity showed a negative one. Thus there was more ¹³⁷Cs in the fish from the oligotrophic lakes than from the eutrophic ones, from the less humic lakes than from the more humic ones, from the more acid than from the less acid ones and from the lakes containing less potassium than from those containing more potassium. The depth, area and volume of the lake did not affect radiocaesium in the fish. Regression equations are presented for predicting ¹³⁷Cs in fish on the basis of environmental data. Fallout, total phosphorus and pH together had the highest influence in multiple regression models but were less significant in the roach than in the perch and pike.     

Benefits of a predtor-induced morphology in crucian carp

Crucian carp (Carassius carassius) develop a deeper body in response to chemical cues from piscivores. This change in body morphology has been suggested to be a predator-induced defence. Here we investigate the possible benefits of the induced body morphology in laboratory experiments. Pike foraging behaviour when feeding on crucian carp of different body depths was recorded using video. Further, in a preference experiment pike were allowed to choose between shallow-bodied and deep-bodied crucian carp of similar lengths. Crucian carp body morphology did not affect predatory behaviours (activity, searching, following, observing, capture success) in northern pike, but an increase in crucian carp body depth led to an increase in handling time in pike. In the preference experiment, pike preferred shallow-bodied crucian carp over deep-bodied. Thus, a change in body morphology, induced by the presence of piscivores, benefits crucian carp by increasing piscivore handling times and an avoidance of the deep-bodied phenotype.     

Fish–duck interactions in boreal lakes in Finland as reflected by abundance correlations

We studied the hypothesis that fish play an important role in lake use by ducks (pairs and broods) in boreal lakes. The study was based on densities of different duck and fish species in 28 boreal lakes in southern Finland. We focused on the three most common duck species (mallard Anas platyrhynchos, green-winged teal A. crecca and common goldeneye Bucephala clangula) and on the three most common fish species (perch Perca fluviatilis, roach Rutilus rutilus and pike Esox lucius) in the region. We considered both competitive and predatory interactions between ducks and fish, the perch and roach being potential competitors with ducks and the pike a potential predator of ducks. We found a negative association between green-winged teal brood density and total fish density, the other duck species having only a weak association with total fish density. When the three fish species were considered separately, a negative association, suggesting food competition, was found between perch, green-winged teal and goldeneye, whereas the role of roach as a food competitor seemed to be of minor importance. We did not find any clear signs of predatory effects of pike on ducks. Our results suggest that food competition is a more important factor than pike predation in affecting lake use by ducks in oligotrophic boreal environments in southern Finland.     

Influence of roundup herbicide on the activities of peptidases in the intestines of various fish species

It has been revealed that, as a rule, Roundup herbicide inhibits activities of peptidases in the intestine mucosa and chyme in various fish species, both benthivorous (common carp Cyprinus carpio, silver bream Blicca bjoerkna, roach Rutilus rutilus, and crucian carp Carassius carassius) and piscivorous (perch Perca fluviatilis, pike Esox lucius, and sander Sander lucioperca). The tolerance of peptidases to the herbicide is species-specific. The magnitude and vector of the effects of Roundup depend on its concentration and localization of an enzyme. In the mucosa, the enzymes of common carp and pike are most tolerant, while the enzymes of common carp, silver bream, and pike are most tolerant in the chyme.     

How many fish populations in Finland are affected by acid precipitation?

Synopsis The number of fish populations affected or lost from small lakes in southern and central Finland due to acid precipitation is estimated. Tolerance limits (pH and labile aluminum) of common fish species were obtained from a fish status survey of 80 lakes. These tolerance values were used to estimate the proportion of affected lakes from the water chemistry data of 783 statistically selected lakes. The proportion of anthropogenically acidified lakes was estimated by calculating pre-acidification pH and aluminum concentrations of the lakes, using a steady-state model based on water chemistry. The number of fish populations for which acidification has affected growth or population structure was estimated at between 2200 and 4400. Out of these, the number of fish populations that have disappeared due to acid precipitation would be about 1000–2000. Almost 60% of the affected or lost populations are roach, Rutilus rutilus, the most sensitive of the common fish species in small lakes in southern and central Finland. Less than 15% of the damaged population is European perch, Perca fluviatilis, the most common species. This is due to the substantially higher tolerance of perch to acidified water in comparison with roach.