Blood values in the pike Esox lucius L.

The ranges and mean values of haematocrit, red cell, white cell and differential cell counts, red/white cell ratio, red cell fragilities, haemoglobin levels and serum protein concentrations of adult pike Esox lucius L. have been measured, and the serum electrophoretic patterns on cellulose acetate and polyacrylamide gel described and discussed. It is hoped that these blood values will provide normal standards for the pike since normal ranges are wide, and isolated measurements therefore of limited value.     

Cannibalism in pike fry, Esox lucius L.: some experiments with fry densities

Pike fry were kept in 0.054-m³ tanks at densities of 50, 100 and 150 (277, 555, 833 fry m⁻²) for seven weeks during which the development of social and feeding behaviour was observed. Zooplankton, macro-invertebrates and perch fry were provided sequentially as food; the pike fry were allowed to feed ad libitum.
Zooplanktivorous fry stopped growing at 22 mm whilst, in the presence of abundant suitable alternative prey, 1–4% turned cannibalistic at 5 weeks of age; cannibals subsequently grew rapidly (mean 1.88 mm day⁻¹). Cannibalism ensued in all tanks when the ratio of predator size: prey size was c .2:1.
Fry tended to space-out evenly in the tanks with no overt aggression or territoriality. Behaviour was typified by remaining still for long periods, particularly subsequent to the onset of cannibalism. Cannibals were attracted by fry movements which often initiated attacks.
Daily per capita mortality rates showed no crowding effects before cannibalism but significant density-dependent mortality due to cannibals. Consumption rates of cannibals varied between 0.63 and 6.0 fry per cannibal per day. Cannibals accounted for 54–96% of daily mortality in the experimental tanks. These results are discussed in relation to proposed mechanisms of pike population density regulation.     

Hydrocephalus and red-disease in pike fry Esox lucius L.

Two diseases of pike fry have been investigated, both causing serious losses in Dutch pike culture. In one of these diseases the lump developing on the head of the fry was associated with an internal hydrocephalus.
The other one, 'red disease' after the haemorrhagic areas in the trunk, may be identical with red-sore disease of pike.
The etiologies of both diseases are unknown.     

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.     

Seasonal anatomical variations in the testes of European pike, Esox lucius L.

The seasonal development of the testes in European pike was examined using wild fish and biopsies from pike housed in tanks. The size of the tubules and the different cell types were measured and their histological appearance described. Four stages of development can be distinguished during the annual cycle. They are: (I) the stage of rest from June to August; (II) the stage of development from September to November with intensive spermatogenesis; (III) the stage of maturity from December to March/April with spermatogenesis completed; and (IV) the post-spawning stage from March to May.     

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).     

Size hierarchy in young pike Esox lucius

Laboratory observations of 20 similar-size sib fry of pike Esox lucius have been carried out. The fishes were kept from June to September in a single aquarium with abundant food. During their life in a limited space, a temporal community formed with a size structure taking the form typical of a hierarchy: five leaders, two outsiders, and eight individuals in an intermediate position. The growth leaders were five cannibal pikes, each having eaten a sib with slower growth—the capture of large prey contributed to a considerable increase in the eater’s growth rate. The effect of hierarchy manifested itself in the mutual influence of pikes onto one another: the presence of large predators hampered the growth of small individuals, while the presence of slowly growing fishes stimulated the growth of leaders.     

The ultrastructure of the blood cells of the pike Esox lucius L.

The ultrastructure of pike peripheral blood cells, lymphocytes, thrombocytes, granulocytes, and monocytes is described. At present there are no reliable criteria for differentiating between round thrombocytes and small lymphocytes of fish on a routine basis. At the ultrastructural level thrombocytes could be clearly differentiated from lymphocytes by cytoplasmic canals and vesicles, marginal microtubules, and large glycogen deposits. Electron microscopic identification of thrombocytes was confirmed by examining the ultrastructural features of a purified thrombocyte fraction. In addition, a preliminary investigation of the structure of the haemopoietic cells in the thymus, anterior kidney, and spleen was carried out.     

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.     

Some characteristics of a pike Esox lucius L. population in an Irish reservoir

A study of a stocked upland reservoir trout fishery, using gill nets, revealed the presence of a large stock of pike and poor trout numbers. The overall growth rate of pike was slow. Two year-classes of pike dominated, but the broad age and length frequency ranges, and the high average weight of individuals were indicative of an unexploited stock. Higher than normal water levels during the spawning period and into the summer period in both 1985 and 1986, coincided with the dominant pike year-classes recorded several years later. This revised version was published online in July 2006 with corrections to the Cover Date.     

The biology of pike, Esox lucius L., in a southern eutrophic lake

The biology of pike, Esox lucius L., in a southern productive lowland lake is described. Scales and opercular bones were difficult to read and interpret, and growth estimated had perforce to be based on scale readings. Growth of Slapton pike is average and intermediate between recorded extremes. Both male and female pike reached maximum condition in February, just prior to spawning. The population of pike of over 450 mm fork length in the lake was estimated at 870·6 ± 389·3 in 1975, and 950·4 ± 143.3 in 1976/77. This leads to the conclusion that the pike population has one of the highest biomasses per surface area of water ever recorded. Number of pike per unit area of surface was also high, despite the fact that a significant proportion of the population (fish under 450 mm) could not be adequately sampled. Mean instantaneous mortality rate was 0·53, and mean instantaneous survival rate was 0·59. The roach provided the main item of diet of the pike, with perch taken less readily. Immature pike ate a significant proportion of invertebrates, but roach was again a common feature of the diet of even small fish. Two spawning migrations were identified; at other times of the year, pike were non territorial. The majority of pike spawned in March. Fecundity of a sample of females was assessed. Overall sex ratio was 1:1.     

Foraging success of juvenile pike Esox lucius depends on visual conditions and prey pigmentation

Young-of-the-year pike Esox lucius foraging on copepods experienced different foraging success depending on prey pigmentation in water visually degraded by brown colouration or algae. Both attack rate and prey consumption rate were higher for E. lucius foraging on transparent prey in brown water, whereas the opposite was true in algal turbid water. Pigments in copepod prey may have a cryptic function in brown water instead of a photo-protective function even if prey-size selectivity was stronger than selection based on pigmentation in juvenile E. lucius.     

Seasonal reproductive cycle of pike, Esox lucius L., from the River Danube

Seasonal changes in ovaries and testes of the pike, sampled in the Danube (at 1163 and 1175 km) were analysed in this research. According to the presence of developing and resting oocytes in histological sections of pike ovaries sampled during August, it is possible to determine which female will be sexually mature the following spring. Active vitellogenesis starts in September (with oocyte diameters of 514 ± 54 μm and 453 ± 68 μm, at the upstream and downstream locality, respectively), at which time the differences between the developing and resting oocytes are even more obvious. Active spermatogenesis starts in September and lasts for 2 months, and by November primarily spermatozoa can be seen in histological sections. The reproductive score points to differences in samples from the two localities that can be explained by the differing characteristics of the habitat. Values of absolute fecundity (AF) ranged from 524 to 123 896 eggs, and the mean value of relative fecundity (RF) was 40.4 ± 12.5.     

The annual reproductive cycle of pike, Esox lucius L., in two Scottish lakes

Histological changes in the ovaries of pike from two shallow, adjacent, Scottish lakes are described and related to a macroscopic scale of maturity stages and to changes in gonad weight. There was no evidence of pre-ovulatory degeneration although occasional residual oocytes were present in spent ovaries. The gonadosomatic index (GSI) was high in males from October to March, and in females it increased through the winter months to a maximum immediately prior to spawning. Maximum ovarian weight was 8.3–9.0% of total body weight compared with only 0.9–1.1% for testes. These GSIs were low compared with other reports for the British Isles, suggesting lower reproductive output. Spawning occurred in the first two weeks of April at a water temperature of 6.0–7.5° C. Fecundity was described from a regression of egg number (F) on fork length (f.l.): log₁₀F= -1.51 + 3.33 log₁₀ f.l. (cm). Mean egg diameter after preservation varied from 1.1 to 2.4 mm over the size range examined. Males were mature at age 2 at a length of ≥ 27 cm, while females first spawned at age 3 at a length of ≤ 28 cm, although a minority were mature at age 2. The sex ratio was 1.2 males: 1 female at Kinord and 1.4 : 1 at Davan. Greater egg production at Davan, 50 678 ha^?1, compared with Kinord, 33 557 ha^?1, was due to higher individual fecundity-at-age resulting from better growth. Fecundity (19.29 × 10³ calculated for a pike of 55 cm F.L.), relative fecundity of only 10–24 eggs per gram wet weight of adult, and GSI values were low compared with pike in North America and Eurasia. Food supply may restrict reproductive output of pike in Lochs Kinord and Davan. The abundance ratio of predator: prey is high with the main prey species, perch, present in low numbers, and the only alternative species is eel in these simple fish communities.     

Acquired hook-avoidance in the pike Esox lucius L. fished with artificial and natural baits

Tagged pike Esox lucius L. in a drainable pond were fished by hook and line, using either a spinner or a small live fish as bait. Catch per unit effort could be used as a measure for catchability because all captured pike were immediately returned to the pond and mortality was low.
Catchability to spinner fishing decreased to very low levels after about half of the population had been caught in this way. Catchability to live bait fishing remained unaffected both by intensive spinner and live bait fishing.
It was difficult to capture pike more than once by spinning. In live bait fishing, on the other hand, the number of recaptures closely matched the number expected if catchability remains unaffected by earlier capture.
The advantages are discussed of the use of artificial baits over live baits in hook and line fishing for pike.     

The effects of insulin on plasma amino acid levels in the Northern pike, Esox lucius L

Cod and bovine insulin (2 i.u. kg⁻¹) were injected intra-arterially into cannulated Northern pike, Esox lucius L. and the levels of 13 plasma amino acids analysed by gas-liquid chroma-tography after 9 and 48 h. Both insulins caused an equally significant reduction in the level of each amino acid after 9 h which was followed by a recovery to near-control levels after 48 h. The data support the hypothesis that insulin plays a major role in the regulation of protein metabolism in this species.     

Cutaneous tumour of northern pike Esox lucius L.: evidence for a monocytic neoplasm

An epidemic of cutaneous tumours occurs in northern pike from the Åland Islands of Finland. Lymphocytes of pike could be triggered to synthesize DNA in vitro by mitogens. Tumour cells had a high basic metabolic rate and mitogens did not enhance their incorporation of ³H-thymidine. High percentages of peripheral blood, spleen, and head kidney mononuclear cells were surface (SIg) and cytoplasmic (CIg) immunoglobulin-positive by indirect immunofluorescence, using rabbit anti-pike IgM antibodies. Lower but still substantially high percentages of SIg and CIg immunofluorescence were observed with mouse anti-carp IgM antibodies. Tumour cells, however, were SIg- and Clg-negative, suggesting that the neoplasm is not a B cell lymphoma or plasmacytoma. A majority of tumour cells exhibited an intense diffuse staining pattern for alpha-naphthyl acetate esterase which was inhibited by sodium fluoride and was reminiscent of that in human monocytes. By electron microscopy (EM), the tumour cells were seen to be closely apposed with a lack of cell-cell junctions, and characteristically contained groups of lysosomes and large numbers of cytoplasmic lipid droplets, which are features of histiomonocytic cells. Although the marker studies do not completely rule out a T-lymphocytic origin, we suggest that the EM findings lend support for the view that the Åland pike neoplasm may be derived from the monocytic lineage.     

The variability of the catch from gill nets set for pike Esox lucius L.

The variability of the catch of pike Esox lucius L. from gill nets in Windermere over the period 1961–71 has been analysed. Altogether 2952 catches have been treated by analysis of variance after an appropriate transformation. A representative value of the residual between catch variance has been used to estimate the reliability of the means of catches based on different numbers of net settings. It is shown that many settings of gill nets are required to get a reliable mean catch.     

Polymorphic tetrameric superoxide dismutase in the pike Esox lucius L. (Pisces; Esocidae).

1. Heart muscle extracts of northern pike from Lake Malaren in Sweden exhibited two electophoretic types of superoxide dismutase, one of which was identified as the cytoplasmic enzyme (s-SOD) and the other as the mitochondrial form (m-SOD). 2. Individual analysis of 51 pike indicated that s-SOD was invariant while m-SOD displayed a pattern of variation which was explicable by a single-locus polymorphism. 3. The observed m-SOD phenotype patterns suggested that the enzyme is a tetramer. This interpretation is supported by in vitro molecular hybridization studies.