Short‐term evaluation of visible implant alpha tags in juveniles of three fish species under laboratory conditions

Visible implant alpha (VI alpha) tag‐induced changes in mortality and condition, as well as tag retention and readability, were examined during a 4‐week period for juveniles of three fish species: tiger muskellunge Esox masquinongy × Esox lucius (91 ± 7 mm total length, L_T, mean ± s.d.), Snake River cutthroat trout Oncorhynchus clarki behnkei (84 ± 8 mm) and rainbow trout Oncorhynchus mykiss (85 ± 5 mm). Mortality and condition did not differ between tagged fish and control fish for any species and overall tag retention rates were high (92% for E. masquinongy × E. lucius, 91% for O. c. behnkei and 100% for O. mykiss). Short‐term readability of VI alpha tags was low in juvenile E. masquinongy × E. lucius and juvenile O. c. behnkei. Therefore, it is not recommend to use VI alpha tags in juvenile E. masquinongy × E. lucius or juvenile O. c. behnkei for periods >2 weeks, but VI alpha tags seem to be suitable for juvenile O. mykiss for a period of at least 4 weeks.     

Development of microsatellite markers for muskellunge (Esox masquinongy) and cross‐species amplification in two other esocids

We report the development of seven polymorphic microsatellite loci in muskellunge (Esox masquinongy) using an unenriched subgenomic library. Polymorphic loci exhibited 2–11 alleles with observed heterozygosities ranging from 0.190 to 0.917 (n = 24). All seven loci amplified by their respective primer pairs resulted in monomorphic products in northern pike (E. lucius) whereas three loci amplified monomorphic products in grass pickerel (E. americanus americanus); these results imply conservation of flanking sequence but loss of polymorphism between these closely related species. Only one of six microsatellite primers developed in a previous study in northern pike amplified polymorphic products in muskellunge.     

Comparison of mouth morphology and prey size selection among three esocid taxa

Aquatic organisms, especially fishes, exhibit exceptional diversity in mouth morphology and this variation has been shown to influence foraging patterns. We compared mouth morphology among muskellunge Esox masquinongy, northern pike Esox lucius and their hybrid, tiger muskellunge E. masquinongy x E. lucius. Head and mouth size among the three taxa were similar for juveniles (<400 mm total length), but diverged with increasing length, being greater for northern pike than muskellunge. Tiger muskellunge had a head and mouth size intermediate to the two, but more similar to northern pike than muskellunge. Morphological differences among taxa were related to data examining prey size selection in laboratory and field experiments. In the laboratory, northern pike selected prey that were smaller than their maximum mouth width (widest point between outside corners of mouth), tiger muskellunge selected larger prey, and muskellunge size-selection was intermediate between the other two taxa. Among the three esocids, muskellunge had the smallest increase in handling time with increasing prey body depth relative to predator mouth width. In a common garden field experiment in three lakes containing mainly deep-bodied prey, results generally followed morphological patterns, with northern pike selecting larger prey compared to muskellunge. Although morphology predicted most of the variation in greatest body depth of prey consumed, the best predictor of prey size was a model that included predator mouth width, taxon, and interaction. Information comparing prey size selection among esocid taxa is useful for understanding how to manage esocid populations based on system-specific prey characteristics and also for understanding how variations in morphological characteristics of apex predators can influence prey vulnerability and ecosystem structure.     

History of muskellunge management in Nebraska

Muskellunge, Esox masquinongy, were first introduced to Nebraska waters in 1958. By 1967 anglers had caught the first muskellunge from Nebraska waters. Hybrid muskellunge, Esox masquinongy × E. lucius, culture and stocking started in 1976. Harvest regulations for muskellunge and hybrid muskellunge were first established in 1977 with a daily bag limit of one muskellunge or hybrid muskellunge of at least 762 mm (30 inches) in length. In 2000 the minimum length limit for muskellunge and hybrid muskellunge was increased to 1016 mm (40 inches). Hybrid muskellunge have been phased out, none have been stocked in Nebraska waters since 2003. Since 1998 muskellunge fingerlings have been held in Nebraska hatcheries until age-1 before stocking. Yearling muskellunge are raised on minnows and other small fish in Nebraska hatcheries and stocking success apparently is very good. Management and research of Nebraska’s muskellunge and hybrid muskellunge fisheries has been limited to routine sampling that has documented the presence of those fish in waters where they were stocked. Fishable populations of muskellunge can now be found in nine Nebraska waters across the state, but most Nebraska anglers are relatively uneducated in fishing techniques for muskellunge, identification, and proper handling.     

Cytological identification of cell types in the testis of Esox lucius and E. niger

Summary Testes of Esox lucius and Esox niger were investigated histologically, cytochemically, and ultrastructurally in reproductive fish. Intralobular Sertoli cells possessed numerous lipid droplets in Esox lucius, but not in Esox niger. In both species, interlobular cell types included myoid cells and lipid-negative Leydig cells within the extravascular space. Evidence is presented for a contractile network of myoid cells within the testes of these teleosts. The presence of Leydig cells and myoid boundary cells in the testis of Esox lucius refutes the reported homology between lobule boundary cells and Leydig cells in this species.     

Trophic flexibility and opportunism in pike Esox lucius

The first comprehensive investigation of pike Esox lucius trophic ecology in a region (Ireland) where they have long been thought to be a non‐native species is presented. Diet was investigated across habitat types (lake, river and canal) through the combined methods of stable‐isotope and stomach content analyses. Variations in niche size, specialization and the timing of the ontogenetic dietary switch were examined, revealing pronounced opportunism and feeding plasticity in E. lucius, along with a high occurrence of invertivory (up to 60 cm fork length, L_F) and a concomitant delayed switch to piscivory. Furthermore, E. lucius were found to primarily prey upon the highly available non‐native roach Rutilus rutilus, which may alleviate predation pressure on brown trout Salmo trutta, highlighting the complexity of dynamic systems and the essential role of research in informing effective management.     

Pike Esox lucius as an emerging model organism for studies in ecology and evolutionary biology: a review

The pike Esox lucius is a large, long‐lived, iteroparous, top‐ predator fish species with a circumpolar distribution that occupies a broad range of aquatic environments. This study reports on a literature search and demonstrates that the publication rate of E. lucius research increases both in absolute terms and relative to total scientific output, and that the focus of investigation has changed over time from being dominated by studies on physiology and disease to being gradually replaced by studies on ecology and evolution. Esox lucius can be exploited as a model in future research for identifying causes and consequences of phenotypic and genetic variation at the levels of individuals, populations and species as well as for investigating community processes.     

Prey capture of pike Esox lucius larvae in turbid water

Pike Esox lucius larvae captured fewer calanoid and cyclopoid copepods in turbid than in clear water, whereas no differences were detected in feeding rates on Daphnia longispina. Decreased capture of copepods may lead to lower growth and survival of E. lucius larvae in turbid areas, in particular, if cladocerans are scarce.     

Non-lethal sampling for stable isotope analysis of pike Esox lucius: how mucus,scale and fin tissue compare to muscle

Stable isotope analysis (SIA) was used to examine the isotopic relationships between dorsal muscle and fin, scale and epidermal mucus in pike Esox lucius. δ¹³C and δ¹⁵N varied predictably within each tissue pairing, with conversion factors calculated for the surrogate tissues, enabling their application to the non-lethal sampling of E. lucius for SIA.     

Comparative lever analysis and ontogenetic scaling in esocid fishes: Functional demands and constraints in feeding biomechanics

When animals grow, the functional demands that they experience often change as a consequence of their increasing body size. In this study, we examined the feeding biomechanics in esocid species that represent different size classes (small, Esox americanus; intermediate, Esox niger; large, Esox lucius), and how their bite forces and associated functional variables change as they grow. In order to evaluate bite performance through ontogeny, we dissected and measured dimensions of the feeding apparatus and the adductor mandibulae muscle complex with its segmentum facialis subdivisions such as the ricto‐malaris, stegalis and endoricto‐malaris across a wide range of body sizes. The collected morphological data was used as input variables for a published anatomical model to simulate jaw function in these fish species. Maximum bite forces for both anterior bite and posterior bite increased in isometry in E. americanus and E. niger. The posterior bite of E. lucius also increases in isometry, however, the anterior bite increases in positive allometry. Intraspecific comparison within E. lucius indicated the increase of bite forces in more developed individuals accelerated after the fish grew out of fingerling stage. In addition, our analysis indicated functional differentiation between subdivisions of the adductor mandibulae segmentum facialis, as well as interspecific differences in the pattern of contribution to the bite performance by these subdivisions. Our study provides insights into not only the musculoskeletal basis of the jaw function of esocid species, but also the feeding capacity of this species in relation to the functional demands it faces as one of the top predators in lake and river systems. J. Morphol. 277:1447–1458, 2016. © 2016 Wiley Periodicals, Inc.     

Photoreceptors and eyes of pikeperch Sander lucioperca,pike Esox lucius,perch Perca fluviatilis and roach Rutilus rutilus from a clear and a brown lake

The photoreceptors and eyes of four fish species commonly cohabiting Fennoscandian lakes with different light transmission properties were compared: pikeperch Sander lucioperca, pike Esox lucius, perch Perca fluviatilis and roach Rutilus rutilus. Each species was represented by individuals from a clear (greenish) and a humic (dark brown) lake in southern Finland: Lake Vesijärvi (LV; peak transmission around 570 nm) and Lake Tuusulanjärvi (LT; peak transmission around 630 nm). In the autumn, all species had almost purely A2-based visual pigments. Rod absorption spectra peaked at c.526 nm (S. lucioperca), c. 533 nm (E. lucius) and c. 540 nm (P. fluviatilis and R. rutilus), with no differences between the lakes. Esox lucius rods had remarkably long outer segments, 1.5–2.8-fold longer than those of the other species. All species possessed middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) cone pigments in single, twin or double cones. Rutilus rutilus also had two types of short-wavelength sensitive (SWS) cones: UV-sensitive [SWS1] and blue-sensitive (SWS2) cones, although in the samples from LT no UV cones were found. No other within-species differences in photoreceptor cell complements, absorption spectra or morphologies were found between the lakes. However, E. lucius eyes had a significantly lower focal ratio in LT compared with LV, enhancing sensitivity at the expense of acuity in the dark-brown lake. Comparing species, S. lucioperca was estimated to have the highest visual sensitivity, at least two times higher than similar-sized E. lucius, thanks to the large relative size of the eye (pupil) and the presence of a reflecting tapetum behind the retina. High absolute sensitivity will give a competitive edge also in terms of short reaction times and long visual range.     

The chromosomes of esox lucius L.

Summary Esox lucius (the pike) is found to have 48 rod-shaped chromosomes with completely terminal centromeres.     

Ecology and management of northern pike in Wisconsin

Northern pike (pike) Esox lucius Linnaeus are broadly distributed across Wisconsin and provide an important sport fishery for anglers. Historical management has included use of angling regulations, stocking, and protection of critical habitat areas. Pike management is often a lower priority in comparison to more intensively managed species such as muskellunge Esox masquinongy Mitchell and walleye Sander vitreous. Pike provide angling opportunities year around, with higher catch rates and live release during open water, and higher harvest rates during winter. While length of pike caught during the two seasons is generally similar, there is some evidence that larger fish are caught during winter months. Results from minimum length limit changes implemented in 1995 have been equivocal and warrant further monitoring using standardized protocol to better determine effects on populations. If natural recruitment is not limited, pike populations can reach high densities and stunting can result. Loss of nearshore habitat has continued at an increased rate as more lake homes are built and shorelines graded, and altered with riprap, sand blankets, or sea walls. If natural recruitment is lacking, fry or fingerling stocking sustains or rehabilitates populations. Most pike stocking occurs in the southeastern portion of the state where habitat loss has been extensive. Stocking in other areas is largely to re-establish populations following a chemical reclamation or from winterkill. Future management needs to establish sampling protocols to ensure comparable data on both a temporal and a spatial scale. Long-term monitoring with these methods is essential to help determine effects of various factors (e.g., regulations, habitat loss) on populations. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Expulsion of miniature radio transmitters along with eggs of muskellunge and northern pike––a new method for locating critical spawning habitat

Identification and protection of critical spawning habitat for muskellunge Esox masquinongy and northern pike Esox lucius is important for preserving the reproductive potential of both species. In this study, we implanted miniature radio transmitters through the oviduct into the egg masses of female muskellunge and northern pike just prior to spawning. This non-surgical procedure was a novel approach for identifying spawning sites when transmitters were expelled with the eggs during egg deposition. Preliminary studies in three lakes showed that muskellunge and northern pike deposited many of the transmitters in likely spawning habitat. An inability to find eggs limited our validation of this method, but nevertheless, a relatively high proportion (70%) of northern pike larger than 690 mm (27.2 inches) expelled transmitters in a previously known spawning area in Willow Lake, Minnesota. Shoreline vegetation in that area consisted primarily of sedges Carex spp., and the adjacent water was shallow with substrate consisting of large mats of water bulrush Scirpus subterminalis. A lower proportion (50%) of muskellunge expelled transmitters in Elk Lake, Minnesota. Water depth at likely spawning sites averaged 1.1 m (3.6 feet) and vegetative cover was variable, but Chara spp. was common to most sites. In Moose Lake, Minnesota, containing sympatric populations of muskellunge and northern pike, 60% of muskellunge and 90% of pike expelled transmitters. Chara spp. beds were the predominant substrate where transmitters were expelled in Moose Lake, but the two species deposited transmitters on deepwater bars (3.7–5.2 m) in addition to shallow near-shore habitat. These results suggest more flexibility in depths used for spawning than typically reported for muskellunge and northern pike.     

Predicting the contributions of novel marine prey resources from angling and anadromy to the diet of a freshwater apex predator

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Effect of boat noise and angling on lake fish behaviour

The effects of disturbances from recreational activities on the swimming speed and habitat use of roach Rutilus rutilus, perch Perca fluviatilis and pike Esox lucius were explored. Disturbances were applied for 4 h as (1) boating in short intervals with a small outboard internal combustion engine or (2) boating in short intervals combined with angling with artificial lures between engine runs. The response of the fish species was evaluated by high‐resolution tracking using an automatic acoustic telemetry system and transmitters with sub‐minute burst rates. Rutilus rutilus swimming speed was significantly higher during disturbances [both (1) and (2)] with an immediate reaction shortly after the engine started. Perca fluviatilis displayed increased swimming activity during the first hour of disturbance but not during the following hours. Swimming activity of E. lucius was not significantly different between disturbance periods and the same periods on days without disturbance (control). Rutilus rutilus increased their use of the central part of the lake during disturbances, whereas no habitat change was observed in P. fluviatilis and E. lucius. No difference in fish response was detected between the two types of disturbances (boating with and without angling), indicating that boating was the primary source of disturbance. This study highlights species‐specific responses to recreational boating and may have implications for management of human recreational activities in lakes.     

Viral infection cycles in pike (Esox lucius L.)

Pike fry weighing 0.2 g were infected with five pathogenic viruses via the water and then fed to one-year-old, 60 g pike. A transer of the viruses from the prey to the predator was demonstrated. The VHS virus produced typical hermorrhages in the muscle of the second nost. Zusammenfassung Zyklische Virusinfektion beim Hecht (Esox lucius L.) Auf dem Wasserweg mit fünf fischpathogenen Viren infizierte Hechtbrut (0,2 g) diente einjährigen Hechten (60 g) als Nahrungsquelle und gewährleistete hierdurch den Virustransfer. Das VHS-Virus induzierte im 2. Wirt typische Hämorrhagien in der Muskulatur. Résumé Cycles d'infection viraie chez le brocket (Esox lucius L.) Des embryons du brochet (0,2 g) inficés par l'eau servaient comme nourriture pour des brochets agés un an (60 g). Par cela le transfer du virus était verifié. Le virus VHS causait dans l'hôte seconde des hemorrhages typiques dans les muscles.     

Potential effects of spawning habitat changes on the segregation of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) and muskellunge (<Emphasis Type="Italic">E</Emphasis>. <Emphasis Type="Italic">masquinongy</Emphasis>) in the Upper St. Lawrence River

Changes in spawning habitat of northern pike (Esox lucius) may affect their segregation from and coexistence with the closely related muskellunge (E. masquinongy). We estimated the areal coverage of robust and shallow emergent vegetation in three shared-spawning bays in the Upper St. Lawrence River from aerial photographs taken from 1948 to 2003. Robust emergent vegetation (e.g., cattail) increased in coverage by 155–241% while shallow emergents (sedges) decreased by 46–96%. The loss of sedges, an important northern pike-spawning habitat, may facilitate greater spawning overlap in offshore-submersed aquatic vegetation within bay habitats used by muskellunge. Development rates and characteristics of northern pike and muskellunge eggs and larvae were compared to better understand the implications of greater spawning overlap. Northern pike eggs developed faster than muskellunge eggs at temperatures of 4.7–19°C, and adhesive eggs and the presence of adhesive papillae were present in both species. Equations were used to predict degree-day requirements for hatching and swim-up in three habitats (shallow emergents, bay, and offshore shoal) along a temperature gradient. Northern pike required more estimated degree days to reach hatching in bay and offshore shoal habitat relative to shallow emergent habitat due to cooler temperatures. Significant spawning overlap is known to occur within bay habitats, but poor success of northern pike in deep bay habitats and overall reductions in abundance are hypothesized to currently buffer muskellunge from potential negative interactions between these species. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

Using accelerometry to quantify prey attack and handling behaviours in piscivorous pike Esox lucius

Accelerometer technology was used to evaluate behaviours in the teleost ambush predator pike Esox lucius foraging on crucian carp Carassius carassius. Automated rule‐based estimates of prey‐size determined handling time were obtained and are compared with video‐recorded behaviours. Solutions to tag attachment and the limitations imposed by battery‐time and data‐logging capacities are evaluated.     

Studies on bucephalid digeneans parasitising molluscs and fishes in Finland I. Ecological data and experimental studies

Two types of bucephalid cercariae are reported from the bivalve Anodonta anatina in two Finnish lakes. One, Type A, resembles in gross morphology the cercaria of Bucephalus polymorphus, and the other, Type B, resembles the cercaria of Rhipidocotyle campanula. Type A daughter-sporocysts develop more slowly, have a greater cercarial productivity and exhibit a differential diurnal rhythm to that of Type B. Cercariae of Type A have a shorter longevity than Type B and tend to encyst in the fins rather than the gill-arches of fish intermediate hosts. The main definitive host of Type A is pike Esox lucius and, in the case of Type B, perch Perca fluviatilis. Adults of Types A and B are morphologically very similar and both species belong to the genus Rhipidocotyle.