Fathead Minnows, Pimephales promelas, Learn to Recognize Chemical Alarm Cues of Introduced Brook Stickleback, Culaea inconstans

In four experiments conducted over a 6-year period, we investigated whether fathead minnows, Pimephales promelas, could acquire the ability to recognize chemical alarm cues of introduced brook stickleback, Culaea inconstans. A laboratory experiment documented that stickleback-naïve minnows did not exhibit an anti-predator response when exposed to the chemical alarm cues of stickleback. In a laboratory experiment conducted 5 years after the introduction of stickleback to the pond, minnows exhibited an antipredator response to stickleback cues. Moreover, in a field experiment the minnows exhibited avoidance of areas labelled with stickleback alarm cues. Minnows raised from eggs taken from the test pond did not exhibit an anti-predator response to stickleback cues while minnows from the test pond that had experience with stickleback cues did respond to stickleback cues. Our results provide clear evidence that cross-species responses to chemical alarm cues of fishes can be learned. Learned recognition of alarm cues has important implications for predator/prey interactions.     

Environmental Conditions and Intraspecific Interference: Unexpected Effects of Turbidity on Pike (Esox lucius) Foraging

Interference among predators decreases per capita foraging rates and has implications for both community dynamics and top-down trophic processes. Interference originates from behavioural interactions among foragers, and these behaviours could be affected by environmental conditions. In experiments on pike foraging alone or among conspecifics in different levels of water turbidity, we expected high turbidity to decrease the perceived risk of intraspecific interactions among pike, and thereby decrease the strength of interference, as turbidity would decrease the visual contact between individuals and act as a refuge from behavioural interactions. The results show that this is not the case, but suggest that interference is induced instead of reduced in high turbidity. Per capita foraging rates do not differ between pike foraging alone or in groups in our clear and moderately turbid treatments, indicating no effect of interference. As high turbidity enhances prey consumption for pike individuals foraging alone, but does not have this effect for pike in groups, high turbidity induces the relative interference effect. We suggest that future evaluations of the stabilizing effects of interference on community dynamics and its reduction of predation impact on top-down trophic cascades should consider potential unexpected effects of environmental conditions.     

Mercury toxicity in livers of northern pike (Esox lucius) from Isle Royale, USA

Many laboratory studies have documented that mercury can be toxic to fish, but it is largely unknown if mercury is toxic to fish in their natural environments. The objective of our study was to investigate the toxic effects of mercury on northern pike (Esox lucius) at Isle Royale, Michigan. In 124 northern pike from eight inland lakes, concentrations of total mercury in skin-on fillets ranged from 0.069 to 0.622 microg/g wet mass (wet wt). Concentrations of total mercury in livers increased exponentially compared with concentrations in fillets, to a maximum of 3.1 microg/g wet wt. Methylmercury constituted a majority of the mercury in livers with total mercury concentrations <0.5 microg/g wet wt, but declined to 28-51% of the mercury in livers with total mercury concentrations >0.5 microg/g wet wt. Liver color (absorbance at 400 nm) varied among northern pike and was positively related to liver total mercury concentration. The pigment causing variation in liver color was identified as lipofuscin, which results from lipid peroxidation of membranous organelles. An analysis of covariance revealed lipofuscin accumulation was primarily associated with mercury exposure, and this association obscured any normal accumulation from aging. We also documented decreased lipid reserves in livers and poor condition factors of northern pike with high liver total mercury concentrations. Our results suggest (i) northern pike at Isle Royale are experiencing toxicity at concentrations of total mercury common for northern pike and other piscivorous fish elsewhere in North America and (ii) liver color may be useful for indicating mercury exposure and effects in northern pike at Isle Royale and possibly other aquatic ecosystems and other fish species.     

Monoamine oxidase activity in embryos of pike (Esox lucius)

1. Mitochondrial MAO specific activity was measured in eggs and early embryos of the teleostean fish Esox lucius using tryptamine, 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA) as substrates. 2. Tryptamine is the most readily deaminated substrate in mitochondria isolated from unfertilized eggs and embryos at the stages of cleavage, blastula and gastrula. 3. Monoamine oxidase activity gradually decreases during development and at the gastrula stage it is respectively 80% (tryptamine), 70% (5-HT) and 50% (PEA) of that found in the egg using the corresponding substrate. 4. The inhibition of egg MAO activity by clorgyline and deprenyl measured in E. lucius eggs using tryptamine as substrate, indicates the presence of a single form of MAO not corresponding to the MAO A and MAO B described in terrestrial vertebrates.     

State-Dependent Mate-Assessment and Mate-Selection Behavior in Female Threespine Sticklebacks (Gasterosteus aculeatus, Gasterosteiformes: Gasterosteidae)

Most investigations of mate-choice have focused on the outcomes of mate-choice (i.e. which mates are chosen), and thus we generally know very little about how mates are chosen (i.e. how mates are found, assessed, and selected). Mate-choice by females has been shown to be dependent on the state of the female, with females being less selective when limited by time or energy. This result could be caused by changes in female mate-assessment or mate-selection behavior. We examined whether manipulations of time and energy affected the mate-choice behavior of female threespine stickleback ( Gasterosteus aculeatus ). We found that female mate-choice behavior, when not divided into stages, was affected by both of the manipulations. This matches previous findings. When we divided female courtship behavior into six stages, we found that the two manipulations affected different portions of the mate-choice process. The holding-time manipulation changed female behavior at the beginning and end of the mate-choice process and the swimming manipulation changed female behavior only at the end of the mate-choice process. Neither of the manipulations significantly affected female behavior in the middle portion of the mate-choice process. Thus, the mate-choice process appears to be composed of multiple state-dependent decisions. We discuss how a better mechanistic understanding of how female state affects female mate-choice behavior can produce testable predictions and provide a basis for investigating the evolution of mating systems.     

Age,growth and life history of Culaea inconstans (Pisces: Gasterostidae) in Delta Marsh Lake Manitoba

Culaea inconstans in delta Area, Lake Manitoba matures in the second summer of life, when between 29 and 65 mm in total length and one year of age. Spawning starts at the end of May after migration into the creeks and channels in the marsh. By June 11–12 the yearlings are under 20 mm in total length. The greatest part of growth is completed in the first summer of life. The asymptotic or average maximum length, L was 89.06 mm. Aging of fish was done by reading otoliths and plotting length frequency histograms. Fish set the first ring, a false check, in otoliths within the first month of life and the annual ring is set by the adults on June 1 of the second summer of life. Culaea inconstans was generally found to be an annual fish which died after spawning in the second summer of life. A high positive correlation coefficient was found for body-otolith relationship. The length-weight regression lines were significantly different from one another and from zero, the F-value being significant at 1% level. The condition factor was found to be variable.     

Persistence of Dactylogyrus eucalius (Monogenea: Dactylogyridae) on the short-lived host Culaea inconstans (Pisces: Gasterosteiformes)

The monogene Dactylogyrus eucalius Mizelle and Regensberger, 1945 and its ability to maintain a population from year to year on the annual fish Culaea inconstans Kirkland was examined in a small lake in central Ontario. Fish were sampled toward the end of their annual breeding season, at a time when the host population consisted of 2 cohorts, i.e., young-of-the-year (0+) and mature adults (1+). Prevalence of infection was 94%, with a mean intensity of 8.8 +/- 9.6; neither measure varied significantly with host length or between cohorts (P > 0.05). At necropsy, parasites were characterized as juveniles that included postoncomiracidia (immature, with a ventrally directed haptor) as well as developing protandrous males (body with a near-complete haptor and with little or no pigmented vitellaria), or as adults (with testis, ovarium, darkened vitellaria, and occasionally bearing a tanned egg). The proportion of juvenile to adult parasites differed significantly between cohorts (P < 0.05), with 0+ fish infected with a mixture of juveniles and adults, whereas 1+ fish had almost exclusively adult parasites. Since adult (1+) brook stickleback typically die after spawning, the increased frequency of juvenile parasites exploiting juvenile hosts may represent an evolutionary adaptation, maximizing the chances of parasites infecting hosts that will enter winter. It is suspected that 0+ fish can be infected in the nest within 2 wk of hatching and persist by effectively infecting new host recruits when they are sympatric with their parents.     

Crystal structure determination and refinement of pike 4.10 parvalbumin (minor component from Esox lucius)

The crystal and molecular structure of the minor component of pike parvalbumins has been determined at 1.93 A resolution by molecular replacement (1 A = 0.1 nm). The crystals are orthorhombic, space group P2(1)2(1)2 with a = 59.62 A, b = 59.83 A and c = 26.35 A. A location of the secondary cation binding site is proposed for this parvalbumin of the beta phylogenetic series.     

Predation of Northern Pike (Esox lucius L.) Eggs: A Possible Cause of Regionally Poor Recruitment in the Baltic Sea

Northern pike (Esox lucius) spawning habitat and egg mortality were studied in three spawning areas in 2001 along the Swedish coast of the Baltic proper: the Blekinge Archipelago, Kalmar Sound and coastal freshwater streams. Spawning peaked during the last week of April in streams, at temperatures ranging from 7.7 to 8.9 °C and during the first week of May in brackish waters, at temperatures ranging from 8.9 to 13.8 °C. Spawning occurred in shallow waters, at depths between 0.2–1.5 m, but generally most of the spawn was found in the shallowest areas. In streams, eggs were mainly attached to emersed vegetation, while in brackish sites pike eggs were well scattered among flooded emersed plants, submersed plants and filamentous algae. Mean egg density varied between 469–1829 m^–2 with the lowest density observed in Kalmar Sound. The calculated egg loss occurring from approximately one day after spawning to one day before hatching ranged from 41±7% in coastal streams to 67±6% in the Blekinge Archipelago and 100% in Kalmar Sound. The significant removal of eggs from spawning sites in Kalmar Sound and Blekinge was most likely due to predation from several fish species. In situ observations and stomach analyses suggested that many pike eggs in Kalmar Sound were lost to the three-spined stickleback (Gasterosteus aculeatus), a species that presently dominate the littoral small fish community. This study therefore suggests that egg predation by sticklebacks and other fishes may be a possible cause of the reported poor recruitment of coastal pike populations in the Kalmar Sound region.     

Fatty acid composition of wild and cultured northern pike (Esox lucius)

The aim of the study was to determine the effect of diet on the fatty acids composition of cultured northern pike (Esox lucius) fillet (mean body weight, 620 g; age, 2.5 years; commercial feed) profiles when compared with wild pike caught in Lake Dga? Wielki in northern Poland (mean body weight, 570 g; age 3.5 years). Cultured pike fillets contained several times more fat (2.40%) compared with wild fish (0.19%, P < 0.01). The total relative quantity of saturated fatty acids (SFA; % of total fatty acids) and unsaturated fatty acids (USFA) in cultured and wild pike were similar. Monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) content differed in wild and cultured fish. Cultured pike contained nearly two times more MUFA (30.90% compared with 15.97%; P < 0.01) but less PUFA (42.04% compared with 58.33%; P < 0.01), n‐3 PUFA (32.42% compared with 41.26%; P < 0.01), and n‐6 PUFA (6.47% compared with 15.79%; P < 0.01). The largest differences were noted with regard to docosahexaenoic acid (DHA) and arachidonic acid (AA), the levels of which in cultured and wild pike were 18.93% vs 27.96% and 0.73% vs 8.60%, respectively (P < 0.01). Quality compositions of the commercial feed and the cultured pike fillets were identical.     

The Adhesive Organ of Larval Pike Esox Lucius L., (Pisces)

Newly hatched pike laryae swim by lateral movements of the trunk. The swimming path is directed upwards. They do not avoid obstacles but interrupt any movements immediately when colliding a substrate. Paired cement glands in rostro-nasal position excrete an elastic connection between larva and the touched substrate. Larvae spend yolk sac stage in a motionless position. The glands were studied by scanning electron microscope, by lightmicroscope and transmission electron microscope. The organs consist of two rostro-lateral areas which have a striking sculptured surface. The glandular cells are of the high prismatic type with basic nuclei and granulae in the apical parts. The granulae are already reduced in size and number after hatching against the prehatching stage. This indicates an early secretory activity before an attachement occured. There are grounds to consider mainly two ecological aspects in favour of pike larvae attached to substrates. One is the distance from the bottom water layers which are often characterized by oxygen deficiency and low water currents. Because pike larvae develop their gills later the gas exchange occurs with the body surface. Favourable water circulation normally exists in some distance from sediment and improves the respiration. The second aspect is governed by immobility and pigmentation which camouflage larvae against predators.     

Chemical Alarm Signals Enhance Survival of Brook Charr (Salvelinus fontinalis) During Encounters with Predatory Chain Pickerel (Esox niger)

A diversity of aquatic organisms release chemical alarm signals when attacked or captured by a predator. These alarm signals are thought to warn other conspecifics of danger and, consequently, may benefit receivers by increasing their survival. Here we experimentally investigated the differences in behaviour and survival of hatchery-reared juvenile brook charr Salvelinus fontinalis that had been exposed to either brook charr skin extract (experimental treatment) or a control of swordtail skin extract (control treatment). Charr exposed to conspecific skin extract exhibited a significant reduction in movement and/or altered their foraging behaviour in the laboratory when compared with charr exposed to swordtail skin extract. We also exposed charr to either water conditioned by a single brook charr disturbed by a predatory bird model or water conditioned by a single undisturbed brook charr. Charr exposed to disturbance signals reduced activity significantly more than charr exposed to chemical stimuli from undisturbed charr. These results demonstrate the existence of both damage-released alarm signals and disturbance signals in brook charr. Wild brook charr also responded to damage-released alarm cues under natural conditions. Charr avoided areas of a stream with minnow traps labelled with conspecific alarm cues vs. control cues. During staged encounters with chain pickerel Esox niger in the laboratory, predator-naive charr fry were better able to evade the predator if they were previously warned by an alarm signal, thus suggesting a survival benefit to receivers. Collectively, these results demonstrate that the presence of alarm signals in brook charr has important implications for understanding predator–prey interactions.     

Growth of pike Esox lucius L. in Lake Rubikiai (Lithuania)

The aim of the study was to determine the growth rate and growth parameters of pike Esox lucius L. in the mesotrophic Lake Rubikiai and to evaluate species growth in light of environmental conditions in Lithuanian lakes of different limnologic types. A total of 204 pike specimens were caught in two subsequent years, April 2005 and April 2006, in Lake Rubikiai. Six age classes (2–7 years of age) for males and 10 age classes (3–12 years of age) for females were identified by scale readings; 2‐ to 4‐year‐old males and 4‐ to 7‐year‐old females prevailed. Total length of pike ranged from 26.5 to 107 cm and weight from 106 to 7600 g. There were no statistically significant differences (Student’s t‐test, P > 0.1) between mean lengths and weights of males and females of the same age. Von Bertalanffy growth parameters for the entire population were: L_∞ = 131.7 cm, k = 0.1530 year^?1, t_o = ?0.0398 year. Calculated overall growth performance index ?′ was 3.42. The length‐weight relationship was described by the equation . The growth rate of pike in Lake Rubikiai was higher than in most other investigated Lithuanian lakes. Pike from Lake Rubikiai are characterized by average growth, compared to other populations from various geographical locations. No significant differences were established between the growth of pike in mesotrophic and eutrophic lakes. Pike growth rate did not correlate with lake surface area, maximum or mean depth, and negatively correlated with bogginess in mesotrophic lakes and limpidity and bogginess in eutrophic lakes (P < 0.05).     

Characteristics and Distribution of Large Tandem Duplications in Brook Stickleback (Culaea Inconstans) Mitochondrial DNA

Most animal mitochondrial DNAs (mtDNAs) range in size from 15 to 18 kb, but increased sizes up to ~40 kb are occasionally found. We investigated large size variation in mtDNA of the brook stickleback fish, Culaea inconstans, and characterized four large (2.7-5.8 kb) tandem duplications. Duplications differ in size, frequency of occurrence, and degree of associated heteroplasmy, but each includes the control region and one or more adjacent genes. Duplications are correlated with two mtDNA lineages sampled from 31 populations. L(1) duplications (3.2-4.8 kb) were present in all lineage I individuals (n = 121, 19 populations); 53 fish were heteroplasmic due to variation in the copy number of a tandemly repeated 270-bp sequence within the duplicated region. In contrast, duplications L(2), L(3), and L(4) (2.7-5.8 kb) occurred in only 117 of 174 lineage II fish, in eight of 14 populations. Nine fish with L(3) or L(4) duplications were heteroplasmic, possessing some mtDNAs that lacked duplications (normal-length mtDNAs). Heteroplasmy in L(2) was associated with a small variable region near the ND5 gene. Phylogenetic analysis of restriction sites in Culaea mtDNAs and haplotype-defining sequence differences present in both copies argue for multiple independent events that gave rise to three of the four duplications.     

Foraging Trade-offs in Fathead Minnows (Pimephales promelas,Osteichthyes, Cyprinidae): Acquired Predator Recognition in the Absence of an Alarm Response

Pike-naive fathead minnows (Pimephales promelas) were fed ad libitum or deprived of food for 12, 24, or 48 h and then exposed to either conspecific alarm pheromone or distilled water and the odour of a predatory northern pike (Esox lucius). Minnows fed ad libitum or deprived for 12 h showed a stereotypic alarm response to the alarm pheromone (increased time under cover objects and increased occurrence of dashing and freezing behaviour); those deprived of food for 24 h showed a significantly reduced alarm response, while those deprived of food for 48 h did not differ significantly from the minnows exposed to a distilled water control. Upon subsequent testing in an Opto-Varimex activity meter, all groups initially exposed to alarm pheromone and pike odour exhibited an alarm response when exposed to pike odour alone. Those initially conditioned with distilled water and pike odour did nor show an alarm response to pike odour alone. These results demonstrate that there exists a significant trade-off between hunger level and predator-avoidance behaviour in fathead minnows and that minnows can learn the chemical cues of a predatory northern pike through association with alarm pheromone even in the absence of an observable alarm response.