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.     

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.     

Lipid content and fatty acid composition of target tissues in wild Perca fluviatilis females in relation to hepatic status and gonad maturation

Variation in liver ultra‐structure and composition in relation to energy mobilization was investigated in female perch Perca fluviatilis from the Meuse River between August 2001 and June 2002. In April, just before spawning, the lipo‐somatic index ( I _F) was 0·3%, the gonado‐somatic index ( I _G) was 28% and the total lipid content of the liver was 2·53%. The average areas of lipid droplets and mitochondria were 0·05 and 0·06 μm², respectively. Glycogen supply reached 7·9% of the total area of the hepatocyte. During the sexual resting period, females accumulated energy in perivisceral fat and in the liver to reach 1·6% I _F and 4·85% of liver lipid content in August with lipid droplets average size of 0·09 μm² and glycogen average area of 15%. Liver cells contained a weakly developed rough endoplasmic reticulum (RER) and a great number of small mitochondria (average size 0·02 μm²). The I _G was 0·6% at this time. During the whole annual cycle, the average lipid content of female liver never exceeded 3·9 ± 1·9%. The concentration of docosahexaenoic (DHA), linolenic and linoleic acids increased in mature gonads while linolenic and linoleic acids decreased in the liver during the same period. Fatty acid composition of muscles of perch was characterized by a high content of DHA.     

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。     

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.     

Yellow perch genetic structure and habitat use among connected habitats in eastern Lake Michigan

Maintenance of genetic and phenotypic diversity is widely recognized as an important conservation priority, yet managers often lack basic information about spatial patterns of population structure and its relationship with habitat heterogeneity and species movement within it. To address this knowledge gap, we focused on the economically and ecologically prominent yellow perch (Perca flavescens). In the Lake Michigan basin, yellow perch reside in nearshore Lake Michigan, including drowned river mouths (DRMs)—protected, lake‐like habitats that link tributaries to Lake Michigan. The goal of this study was to examine the extent that population structure is associated with Great Lakes connected habitats (i.e., DRMs) in a mobile fish species using yellow perch as a model. Specifically, we tested whether DRMs and eastern Lake Michigan constitute distinct genetic stocks of yellow perch, and if so, whether those stocks migrate between the two connected habitats throughout the year. To do so, we genotyped yellow perch at 14 microsatellite loci collected from 10 DRMs in both deep and littoral habitats during spring, summer, and autumn and two nearshore sites in Lake Michigan (spring and autumn) during 2015–2016 and supplemented our sampling with fish collected in 2013. We found that yellow perch from littoral‐DRM habitats were genetically distinct from fish captured in nearshore Lake Michigan. Our data also suggested that Lake Michigan yellow perch likely use deep‐DRM habitats during autumn. Further, we found genetic structuring among DRMs. These patterns support hypotheses of fishery managers that yellow perch seasonally migrate to and from Lake Michigan, yet, interestingly, these fish do not appear to interbreed with littoral fish despite occupying the same DRM. We recommend that fisheries managers account for this complex population structure and movement when setting fishing regulations and assessing the effects of harvest in Lake Michigan.     

Summer co‐existence of small‐sized cyprinid and percid individuals in natural and impounded stretches of a lowland river: food niche partitioning among fishes

Due to changes of discharge regime downstream of a dam reservoir, an alluvial natural stretch of the Warta River changed to a macrophyte‐dominated ecosystem. Large patches of submersed, aquatic macrophytes appeared in summer and their effect is analysed in this study. These patches contained enriched macroinvertebrate assemblages (epiphyton and benthos) and they were refuge for both zooplankton and young fishes released from the reservoir. Despite these altered conditions in this stretch, roach Rutilus rutilus, perch Perca fluviatilis and ruffe Gymnocephalus cernua dominated, as they did in the natural backwater. Fishes were sampled every 2 weeks from June to August, together with their food resources to assess the partitioning of the diet among small individuals of the three species in both stretches (the natural and affected ones). The aim of the analysis was to answer how animal food associated with water plants was partitioned between the species. In both stretches, G. cernua were primarily benthivorous, but epiphytic fauna, zooplankton and large‐sized benthic chironomid larvae replaced lack of many large, benthic insects in the tailwater. Levins' food breath index decreased from 0·36 in the backwater to 0·29 in the tailwater. An opposite trend was observed for P. fluviatilis occurring among macrophytes. Perca fluviatilis were competitors of R. rutilus and took food not only in or on the river bed, but also in the water column. They ate zooplankton and epiphytic fauna and Levins' index increased from 0·32 to 0·44 in the tailwater. Rutilus rutilus fed on adult insects, algae and plant fragments in the natural stretch. In the tailwater, these food types were chiefly complemented by zooplankton. Despite this, the niche breadth of R. rutilus was similar at the two sites. Abundance of food associated with the macrophytes appeared to facilitate cohabitation in the abundant fish populations, but P. fluviatilis appeared to benefit the most in the altered river stretch.     

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.     

Use of Biochronology to Examine Interactions of Freshwater Drum, Walleye and Yellow Perch in the Red Lakes of Minnesota

Growth histories for freshwater drum, Aplodinotus grunniens, walleye, Stizostedion vitreum, and yellow perch, Perca flavescens, were constructed using calcified structures for the period 1947 through 1996 for the Red Lakes, Minnesota. Increased walleye growth and decreased yellow perch growth were observed over the period from 1983 to 1996, which are attributed to intensive fishing resulting in decreased intraspecific competition in walleye and increased intraspecific competition in yellow perch through release from predation. Strong year-classes of yellow perch were positively correlated with walleye growth (r=0.57, p-value=0.042). There was no evidence for interactions of walleye or yellow perch with freshwater drum. Freshwater drum growth (r=0.680, p-value=0.0001) was more highly correlated with temperature than were walleye (r=0.386, p-value=0.006) and yellow perch growth (r=0.303, p-value=0.036).     

Diel variation in habitat use by planktivores in field enclosure experiments: the effect of submerged macrophytes and predation

The importance of submerged macrophytes and predation risk for habitat use by 0+ perch ( Perca fluviatilis ) and 0+ roach ( Rutilus rutilus ) was investigated in triplicate 78-m² field enclosures with and without macrophytes in the middle. During three experimental runs, habitat use by fish were monitored every 6 h with Breder traps. Each period included 2 days of fish monitoring before stocking with piscivorous perch, and 2 days after. Predation risk significantly changed habitat use by 0+ perch in the morning, midday and evening, but not at night. By comparing with the unvegetated controls, we found a refuging effect of macrophytes in the morning. Under predation risk there was significant diel variation in habitat use by 0+ perch, suggesting a migration from the open water habitat at night into the macrophytes in the morning. Roach continued to use open water even after predators were stocked, but responded like perch by reducing overall activity.