The role of sense organs in the feeding behaviour of Chinese perch

Experiments were conducted to identify the roles of the individual sense organs in the feeding behaviour of Chinese perch Siniperca chuatsi by determining the consumption of natural food after selective removal or blocking of eyes, lateral lines and olfactory organs, and also by observing the behavioural response to visual, mechanical and chemical stimulation by artificial prey. Chinese perch were able to feed properly on live prey fish when either eyes or lateral lines were intact or functional, but could scarcely feed without these two senses. Chinese perch recognized its prey by vision through the perception of motion and shape, and showed a greater dependence on vision in predation when both visual and mechanical cues were available. Chemical stimulation by natural food could not elicit any feeding response in Chinese perch, and gustation was only important to the fish for the last stage of food discrimination in the oropharyngeal cavity. The sensory basis of Chinese perch in feeding is well adapted to its nocturnal stalking hunting strategy, and also explains its peculiar food habit of accepting live prey fish only and refusing dead prey fish or artificial diets.     

Growth responses of age 0 white perch and yellow perch from field-enclosure experiments

In this paper, we investigate the potential for competition between age 0 white perch Morone americana and yellow perch Perca flavescens in field-enclosure experiments. In 1986 and 1987, different densities of white perch and yellow perch were stocked into cages in the western basin of Lake Erie and their growth responses determined. Fish were weighed and measured pre- and post-stocking. In 1986 when fish were food-limited, individual growth of both species were negatively affected by increased total fish density; yellow perch to a greater extent. In 1987, experiments were carried out later in the year at lower temperatures. Yellow perch were shown to feed and continue to grow at lower water temperatures than white perch. We conclude that competition in summer may be mitigated in the fall because of differences in thermal optima between these two species.     

Effect of group size on feed intake, growth and feed efficiency of juvenile perch

Feed intake, growth and feed efficiency of juvenile perch Perca fluviatilis were significantly affected by group size, with fish in groups of 12 having lower feed intake, higher growth and higher feed efficiency than solitary individuals. The same trend was seen for fish in groups of 12 compared to fish in groups of four, and for fish in groups of four compared to solitary individuals, although the differences were not always significant. The high growth and low feed efficiency for fish in groups may be caused by benefits obtained from shoaling such as reduced levels of stress.     

Social learning enhances search image acquisition in foraging brook trout

Brook trout feed primarily on prey items for which they have developed a search image. Periodically, fish are required to update their search images to match temporal variability in prey abundance. It is currently unknown how brook trout develop search images, but there is evidence to suggest that it could be influenced by social learning, wherein a fish learns a novel behavior through observation alone. Here we demonstrate that adult brook trout use social learning to quickly develop search images for novel prey. We trained a set of demonstrators to develop a search image for canned mealworms and subsequently moved demonstrators to treatment pools that contained naïve bystanders. We also had control pools that contained naïve bystanders and sham demonstrators that had not been trained on mealworms. Over an 8-day period, bystanders in treatment pools consumed 68 % of mealworms, compared to only 36 % in control pools. Moreover, social learning of search images was rapid as bystanders in treatment pools began feeding on mealworms in less than 1 day, whereas it took 7 days for bystanders in control pools to feed heavily on mealworms. Social learning of search images confers an adaptive advantage by reducing energetic costs of foraging.     

Growth,morphological variation and ontogenetic niche shifts in perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis>) in relation to resource availability

Despite the common occurrence of ontogenetic niche shifts, their consequences for morphological adaptations have been little studied. To address this question, we studied morphological adaptations related to ontogenetic niche shifts in Eurasian perch (Perca fluviatilis) in eight lakes that varied in density of benthic resources and planktivorous fish biomass. Perch start to feed on pelagic zooplankton, then shift to benthic resources at intermediate sizes, and finally, when large enough, mainly feed on fish. These three functional niches over ontogeny are expected to set constraints on the morphology and size-specific growth of perch. The growth of perch was negatively related to planktivorous fish biomass in the zooplanktivorous niche, but positively related to planktivorous fish biomass in the piscivorous niche. The number of gill rakers of perch was negatively related to the biomass of planktivorous fish, providing evidence for the occurrence of character displacement as a consequence of competition in the zooplanktivorous niche. Perch in lakes with low densities of predator-sensitive macroinvertebrates had greater body height measurements and a larger mouth early during ontogeny. This pattern is suggested to be a result of a selection for increased efficiency in the benthic niche when the availability of benthic resources is low. Perch in lakes with a high biomass of planktivorous fishes had fusiform body morphology, a thicker tail and a larger mouth then the average piscivorous perch. The different responses of perch morphology to variation in the availability of benthic resources compared to variation in planktivore biomass are suggested to be partly because the availability of the former resource to a larger extent is set by abiotic conditions (humic content). We suggest that the key factors affecting size-specific growth and body morphology of perch in the system studied are the availability of resources in the benthivorous and piscivorous niches. We also provide evidence for morphological trade-offs, especially between the benthivorous and the piscivorous ontogenetic niches. Received: 6 July 1999 / Accepted: 8 September 1999     

The effects of nymphaeid (Nuphar lutea) density and predation by perch (Perca fluviatilis) on the zooplankton communities in a shallow lake

1. The effects of addition of juvenile perch (Perca fluviatilis) on the microcrustacean and rotifer communities associated with nymphaeid beds were studied, at three different plant densities [high (normal), medium (reduced by a half) and low (reduced to a third of normal)], in eighteen 2 m × 1 m enclosures in a shallow lake. 2. At the low and medium densities of lilies, Daphnia densities were high in the absence of perch but very low in the presence of perch. They increased, even in the presence of perch, to high densities (comparable with those in the absence of perch) at the highest plant density. Body sizes of Daphnia hyalina were consistent with high predation by perch at low and medium plant densities but reduced predation at high plant densities. Patterns of chlorophyll a concentration, in the presence of perch, inversely reflected those of D. hyalina density. 3. At naturally high densities but not at reduced densities, the plants appeared to act as refuges against predation for the Daphnia. Reductions in oxygen concentrations in the plant beds were not responsible for the refuge effect, nor could there be avoidance of the beds by the fish. The mechanism of the refuge effect must therefore lie in frustration of the process of capture of the Daphnia by the fish. 4. Numbers of other small Crustacea and rotifers were mostly unaffected by fish predation. Numbers of Asplanchna sp., Chydorus sphaericus and copepodites were higher in the presence of fish and, although there was no main effect of fish on numbers of Diaphanosoma brachyurum, there was a plant–fish interaction, with this species being less abundant in the presence of fish at low plant densities but more abundant in the presence of fish at medium and high plant densities. Main effects of plants were few, with only Asplanchna sp. and Keratella sp. decreasing in numbers with increasing plant density. Most taxa changed in numbers with time but interaction effects between time and plants, and fish and plants, were few.     

The tilapiine fish stock of Lake Victoria before and after the Nile perch upsurge

Since the beginning of fisheries in Lake Victoria, two native tilapiine species, Oreochromis esculentus and Oreochromis variabilis , were the main target of the local fishermen. A continuous increase in fishing pressure led initially to a declining catch per unit of effort, and a smaller average fish size; eventually, there was a reduced landing of tilapiines. To boost the fisheries, three alien tilapiine species and the Nile perch Lates niloticus were introduced. Thirty years after its introduction, Oreochromis niloticus appeared to be the most successful tilapiine species. It replaced the indigenous tilapiines almost completely before the Nile perch came to dominate the ecosystem of Lake Victoria. Reduced fishing pressure on the tilapiines in the 1980s, due to the shift of the local fishery towards the Nile perch, resulted in an increase in the stock of O. niloticus and an increase in average fish size. Subsequently, the total mass of O. niloticus landed increased. The stocks of the indigenous tilapiines did not recover but declined to extremely low levels, or vanished from the main lake. Currently, these species still occur in satellite lakes of Lake Victoria, from which O. niloticus is absent. Nile perch feed on O. niloticus; however, the limited overlap in distribution between piscivorous Nile perch and O. niloticus of consumable sizes is probably an important factor in explaining the coexistence of the two species. The main cause of the disappearance of the native tilapiine species is presumed to be competitive dominance by O. niloticus .     

The effect of shelter on welfare of juvenile Atlantic salmon Salmo salar reared under a feed restriction regimen

This study investigated whether shelter (presence or absence) affected the frequency of fin damage in Atlantic salmon Salmo salar exposed to feed restrictions (0·73 or 0·33% of body mass day^?1). The presence of shelter had a positive effect on the pectoral fins at both feed ration levels and on the dorsal fin at the higher ration level but it had a negative effect on survival. The reduced feed rations resulted in fish of the same size and nutritional status as wild fish. The provision of shelter has potential to mitigate the negative effects of feed restrictions on fin quality, but the optimal shelter design requires some additional investigation.     

Competition in Umbra-Perca fish assemblages: experimental and field evidence

Summary One potentially important effect of interspecific competition in freshwater fish communities is to increase predation intensity from gape-limited piscivores by lowering growth rates of prey species. We investigated the operation and consequences of competition between central mudminnows (Umbra limi) and yearling yellow perch (Perca flavescens) in a system where size-limited predation on mudminnows by larger perch is a principle structuring mechanism. During laboratory experiments in which mudminnows foraged for patchily-presented food in the presence and absence of yearling perch, the food intake of mudminnows decreased at both the population and individual-fish levels when perch were present. Mudminnows were neither less active nor did they occupy lower-quality food patches in the presence of perch; exploitation competition, rather than interference or predator avoidance, appeared responsible for reduced feeding success. To assess effects of competition in the field, we examined size distributions and condition factors of yearling mudminnows and perch in small Wisconsin lakes having mudminnow-only and mudminnow-perch assemblages. Yearling mudminnows were smaller and in poorer condition in an assemblage composed (by mass) of 45% yearling perch than in two mudminnow-only assemblages. Conversely, yearling perch were larger and in better condition when the mudminnow-perch assemblage contained only 45% perch then when it contained 92% perch. Our experimental and field results indicated that an asymmetrical competitive relationship could contribute directly to the interspecific population dominance of perch over mudminnows in Umbra-Perca assemblages through reduced food intake, growth, and condition of mudminnows, and indirectly through increased vulnerability of mudminnows to size-limited predation.     

Evidence for negative impact of plerocercoid infection of Triaenophorus nodulosus on Perca fluviatilis L. stock in Upper Lake Constance, a water body undergoing rapid reoligotrophication

The macro-pathological impact of plerocercoid infection of perch Perca fluviatilis livers was quantitatively determined by an index of liver lesion ( I _LL) in fish from Upper Lake Constance (ULC). These results were compared to the I _LL values of perch from two other lakes. From February to November 1999, 2071 perch were examined from the three sites. Prevalence of infection in ULC was 13% in actively growing first year (0+ year) perch and 94% in older fish, whereas in the two lakes used for comparison the figures for 0+ year perch were 12 and 20%, and in older fish 62 and 60%, respectively. Infected livers from perch caught in ULC revealed significantly higher I _LL values than those of fish from the other two lakes. Perch livers from ULC containing more than three Triaenophorus nodulosus larvae also showed significantly more serious pathological alterations than uninfected livers or those with normal infection levels of one to three T. nodulosus . In all three lakes, excluding heavily infected perch from ULC, 0+ year perch livers revealed little or no damage, whereas in livers of older perch pathological alterations were apparent. In addition, analysis of age and total length data showed that perch infected with one to three parasites in ULC grew significantly slower than uninfected ones, and severely infected perch (greater than three parasites) grew significantly slower than those with a normal parasite load. With respect to mass, growth of ULC fish suffering normal infection (49% of all adults) was reduced by 9% and in those with severe infections (45% of all adults) growth was 16% below expected at normal harvesting age.     

A trophic bottleneck?: The ecological role of trout‐perch Percopsis omiscomaycus in Saginaw Bay,Lake Huron

Trout‐perch are abundant in many North American aquatic systems, but the ecological roles of trout‐perch as predators, competitors and prey remain relatively understudied. To elucidate the ecological role of trout‐perch in Saginaw Bay (Lake Huron, North America), the spatial and temporal diet composition was quantified and the frequency of occurrence of trout‐perch in diets of piscivorous walleye and yellow perch was evaluated. From May through November 2009–2010, trout‐perch and their potential predators and prey were collected monthly from five sites in Saginaw Bay using bottom‐trawls. Trout‐perch were abundant components of the Saginaw Bay fish community, and in 2009, represented 13.5% of fish collected in trawls, with only yellow perch (38%) and rainbow smelt (19.1%) being more common. Trout‐perch primarily consumed Chironomidae (84.0% of diet biomass) and exhibited strong, positive selection for Chironomidae and Amphipoda, suggesting that their diet preferences overlap with the economically important yellow perch and juvenile walleye. Energy content of trout‐perch averaged 4795 J g^?1 wet and was similar to yellow perch (4662 J g^?1 wet) and round goby (3740 J g^?1 wet). Thus, they may provide a comparable food source for larger piscivorous fish. However, despite their high energy density, abundance, and spatial overlap with other fish prey species, trout‐perch were very rare in diets of piscivorous walleye and yellow perch in Saginaw Bay, indicating that trout‐perch are a weak conduit of energy transfer to higher trophic levels.     

Effects of infochemicals released by gape-limited fish on life history traits of Daphnia: a maladaptive response?

Life history shifts in daphnids in response to fish infochemicalsare generally interpreted as an adaptive response to positivesize-selective predation. This interpretation does, however,not hold for larval and small juvenile planktivorous fish, whichdue to gape limitation, feed on small and medium sized prey.In a life table experiment we show that daphnids exposed toinfochemicals excreted by small gape-limited perch and largerperch changed their life history in the same direction, irrespectiveof the contrasting size-selection of the fish. However, responsesto fish infochemicals were strongly influenced by food conditionsfor daphnids. In the high food treatments size at maturity wasin the presence of fish infochemicals, whereas age at maturityremained unchanged. Under low food conditions, size at maturitywas generally smaller compared with the high food situation,but unaffected by fish infochemicals. By contrast, age at maturity,which was increased at low food levels, was significantly lowerin fish treatments compared with the control. We conclude thatlife history responses of daphnids to gape-limited fish canindeed be maladaptive, but only in situations of high food availability.This combination of factors is, however, rather unlikely becausegape-limited fish usually occur in late spring during the clearwater phase when daphnids are severely food limited. We thushypothesize that the costs of this maladaptive response undernegative size-selective predation will be low under field conditionsand the selective advantage under positive size-selective predationlater in the season will outweigh these costs.     

Diet and Food Web Support of the White Perch, <Emphasis Type="Italic">Morone americana</Emphasis>, in the Hackensack Meadowlands of New Jersey

Synopsis I analyzed stomach contents of white perch, Morone americana, caught throughout the year in the Hackensack River in northern New Jersey. The dominant prey items were amphipods, with shrimp and fish being less important. Stable isotope analysis indicated that the primary producers of importance in the food web leading to white perch were benthic or planktonic microalgae and secondarily Phragmites australis, the dominant macrophyte in the Hackensack Meadowlands. Despite their large size, white perch do not generally appear to feed any higher in the food web than killifish, Fundulus heteroclitus.     

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.     

Effects of stress on growth, cortisol and glucose levels in non-domesticated Eurasian perch (Perca fluviatilis) and domesticated rainbow trout (Oncorhynchus mykiss)

Eurasian perch (Perca fluviatilis) is a promising aquaculture candidate, but the growth performance of this non-domesticated species may be negatively affected by its stress responsiveness to intensive culture conditions. To evaluate this potential problem, juvenile Eurasian perch were exposed to a standardized handling stressor twice a week for an 8-week period. A similar study was conducted on domesticated rainbow trout (Oncorhynchus mykiss) for comparison of intra- and inter-specific differences. The stressed fish of both species showed lower body growth than the non-stressed control fish, however, the final mean body mass was 35.4% lower in the stressed Eurasian perch than in the non-stressed controls, compared to 22.8% difference between the two groups in rainbow trout. The stress responsiveness was examined by comparing the post-stress cortisol and glucose levels in repeatedly stressed fish and fish exposed to the stressor only once. The cortisol stress response in both species strongly indicated a habituation to the repeated stressor. Thus, repeatedly stressed Eurasian perch reached maximum cortisol levels of 130 ng/mL after 0.5 h compared to 200 ng/mL in the fish stressed once, while considerably smaller differences in cortisol levels were shown between the repeatedly and single stressed rainbow trout. Rainbow trout also showed lower post-stress glucose levels in the repeatedly stressed fish compared to the single stressed fish. In contrast, the glucose levels in both groups of Eurasian perch increased abruptly after stress treatment and remained elevated at approximately 19 mM for 6 h; levels were three times as high as the peak levels 3 h post-stress in rainbow trout. Together, the habituation of the stress response shown in both species did not eliminate the growth difference found in the repeatedly stressed fish versus the control fish. Further, the lower growth performance of Eurasian perch compared to rainbow trout could partly be due to the increased energy consumption in the more stress responsive Eurasian perch.     

The use of integrated constructed wetlands (ICW) for the treatment of separated swine wastewaters

Haplochromine cichlids used to be the main prey of the introduced Nile perch, Lates niloticus, in Lake Victoria. After depletion of the haplochromine stocks at the end of the 1980s, Nile perch shifted to the shrimp Caridina nilotica and to a lesser degree to its own young and the cyprinid Rastrineobola argentea. In the present study, we investigated the Nile perch diet in the northern Mwanza Gulf after resurgence of some of the haplochromine species and compared it with data collected in the same area in 1988/1989. It became clear that haplochromines are again the major prey of Nile perch. The dietary shift from invertebrate feeding (shrimps) to feeding on fish (haplochromine cichlids) occurs at a smaller size than it did when Nile perch were taking primarily dagaa and juvenile Nile perch as their fish prey. The apparent preference for haplochromines as prey has reduced the degree of cannibalism considerably, which may have a positive impact on Nile perch recruitment.     

Conformist learning in nine-spined sticklebacks' foraging decisions

Theoretical analyses have reported that in most circumstances where natural selection favours reliance on social learning, conformity (positive frequency-dependent social learning) is also favoured. These findings suggest that much animal social learning should involve a copy-the-majority strategy, yet there is currently surprisingly little evidence for conformist learning among animals. Here, we investigate this possibility in the nine-spined stickleback (Pungitius pungitius) by manipulating the number of demonstrator fish at two feeders, one rich and one poor, during a demonstration phase and evaluating how this affects the likelihood that the focal fish copy the demonstrators'' apparent choices. As predicted, we observed a significantly increased level of copying with increasing numbers of demonstrators at the richer of the two feeders, with copying increasing disproportionately, rather than linearly, with the proportion of demonstrators at the rich foraging patch. Control conditions with non-feeding demonstrators showed that this was not simply the result of a preference for shoaling with larger groups, implying that nine-spined sticklebacks copy in a conformist manner.     

Nutrition and feeding of yellow perch (Perca flavescens)

Yellow perch ( Perca flavescens ) have become one of the focal points in aquaculture in the Great Lakes region of the United States. In this paper, we reviewed existing information on nutrition of yellow perch and identified critical areas in need of development. Yellow perch are small at hatching (4–7 mm total length), and are difficult to feed. Zooplankton cultures remain the only viable means of mass propagation, but larvae can be trained to accept formulated feeds in ponds at the age of 30–45 days. Few nutritional requirements exist for yellow perch, thus there are no diets formulated specifically for this species. The current recommendations are use of feeds formulated for trout and salmon. Ongoing research efforts are underway that will improve our ability to feed yellow perch at all life history stages.     

Social enhancement and social inhibition of foraging behaviour in hatchery-reared Atlantic salmon

The results of two experiments showed that observation of a trained conspecific Atlantic salmon Salmo salar significantly increased the rate at which naïve hatchery-reared fish accepted novel, live prey items, whereas the presence of an untrained conspecific actually decreased learning rates due to social inhibition. Pre-release training involving exposure of hatchery-reared fish to live prey items in the presence of pre-trained demonstrators would result in a significant enhancement in their foraging success on release and help prevent starvation, which is thought to be one of the principal causes of post-release mortality in hatchery-reared fishes.     

Long-term stability in the population levels of the eyefluke Tylodelphys podicipina (Digenea: Diplostomatidae) in perch

Annual changes in the population size of the metacercariae of Tylodelphys podicipina in the eyes of perch in a small eutrophic lake were studied over ten years by following changes in prevalence, abundance and overdispersion of parasites throughout the life of each year class of fish. The population increased rapidly in the first two years after its introduction to the lake, but for the next six years fluctuated within very narrowly constrained limits before declining as a result of a catastrophic decline in the perch population. No evidence of parasite-induced host mortality was found: the decline in parasite abundance throughout the life of each year class was due to density-independent parasite mortality within the fish as a result of natural variation in the life span of the metacercariae. Levels of infection in the first year of a year class were determined principally by transmission processes, as transmission could only occur over a very brief period when release of cercariae from parent generation snails coincided with the presence of perch fry. Transmission appeared to be density-independent, and infection levels in perch to be determined by the dimensions of the transmission' window' and subsequently modified by parasite mortality. No evidence of host responses or any other regulatory factor of fish origin was found, and the infrapopulations in perch appear to be non-equilibrial and unstable. Although the possibility of regulatory processes acting on infrapopulations of the parasite in other hosts remains, the importance of transmission windows in determining infrapopulation levels in fish is emphasized.