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.     

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.     

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 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.     

Primary structure of protamine from the Northern pike Esox lucius

The basic nuclear protein in the sperm of the Northern pike is a protamine, 32-residues long, which behaved as a single component during ion-exchange chromatography and gel electrophoresis. Amino acid analysis gave close to molar ratios for the eight different residues with no evidence of microheterogeneity. However, the presence of sequence variants was revealed following a combination of automated protein sequencing and cleavage of the protamine by CNBr, endoproteinase Lys-C and thermolysin. At position 28 there is an equal probability of having serine or glycine. At position 9 glycine is found more frequently than serine. The reciprocal nature of the substitutions results in glycine and serine contents which are close to a 4:2 ratio. Pike protamines are homologous to those of the trout but show less sequence variation between components.     

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).     

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.     

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.     

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.     

Wetlands for northern pike (Esox lucius L.) recruitment in the Baltic Sea

In recent decades, wetlands have been constructed or restored around the Baltic sea to counteract the eutrophication of its coastal waters. Some of these wetlands could also be suitable spawning and nursery areas for anadromous northern pike (Esox lucius L.). We studied juvenile pike production in three coastal wetlands along the south-eastern coast of Sweden that were restored in different ways. Where terrestrial vegetation was temporarily flooded, pike larval/juvenile emigration increased from a few thousand individuals before restoration to over a hundred thousand afterwards. We suggest that vegetation was the key to this successful reproduction, as wetlands where vegetation was removed or reduced saw no similar increase in pike production. Flooded vegetation in shallow waters offers optimal spawning conditions, increased food resources, and refuge from predation. The growth and emigration of larvae and juveniles were followed over time, revealing that 80–95% of individuals left the wetlands within 1 month (at a size <6 cm). This emigration probably represents an adaption to seasonally decreasing water levels but may also be a way to avoid cannibalism.     

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.     

Experimental studies on some trophic relationships in juvenile pike, Esox lucius L.

A postprandial increase in ammonia nitrogen excretion and oxygen consumption rates was observed in juvenile pike fed a natural diet or an artificial dry diet. Specific growth rate of natural diet fed pike (2.4%) was lower than that of pike fed the artificial diet (3.1%). Fifty per cent of ingesta was evacuated within 5–6 h in pike of 25 mg body weight and 9–10 h in those weighing 150mg. Daily nitrogen excretion rates were related to body weight. Respiratory quotient and energy retention efficiency were affected by the nature of the diet ingested by pike. Parameters of the energy balance (losses, retention, increment due to feeding) were related to energy intake.     

The anatomy and histology of the alimentary tract of the carnivorous fish the pike Esox lucius L.

The alimentary tract of the pike is described, relating its feeding habits to its intestinal gut histology. It is a carnivorous species having a short oesophagus, pouch-like stomach and a short intestine with two convolutions. Stratified epithelium with columnar cells and many goblet cells are present in the oesophagus, columnar epithelial cells only in the stomach, and both cell types in the intestine.
Eosinophils in the mucosa of the oesophagus originate from connective tissue cells and lymphocytes and neutrophils are present. The lamina propria is composed of a stratum granulosum, stratum compactum, blood vessels and loose areolar tissue. The stratum compactum is a strengthening substance, composed of collagen, characteristic of carnivorous teleosts. The circular and longitudinal muscle layers and serosa are similar to those of other carnivorous teleosts.
The pancreas and liver are briefly described, the pancreas being the unusual compact type not often found in teleosts. The B cells are seen in the periphery and a cells in the centre of the islets. The liver is a unilobular organ, having oil storage as a major function.
The distribution of goblet cell mucin is given, differentiating it into neutral and acid mucosubstances. Nine levels of alimentary tract were examined in the mucin distribution study. The functions of mucin in the pike are digestion, absorption, protection and lubrication.     

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 starvation and force-feeding on the metabolism of the Northern pike, Esox lucius L.

The effects of starvation and force-feeding on certain tissue and blood constituents were studied in the Northern pike, Esox lucius L. Starvation resulted in a reduction of liver and muscle glycogen and liver lipid. Blood glucose concentration and haematocrit were reduced, total plasma cholesterol levels were increased, while the levels of plasma free fatty acids (FFA), amio acid nitrogen and protein remained unaltered. No significant changes were observed in either muscle protein, muscle water or the response to amino acid loading during the starvation period.
The force-feeding of pike starved for 3 months resulted in liver lipid and muscle glycogen being increased to levels higher than those observed in freshly-captured fish. Liver glycogen, however, increased to values only slightly higher than those of starved animals. Furthermore, while force-feeding had little effect on plasma FFA or protein concentrations, blood glucose, plasma cholesterol and haematocrit returned to the levels found in freshlycaptured fish and those of amino acid nitrogen were higher.
The results indicate that pike are well adapted for periods of prolonged starvation and that hepatic and extra-hepatic lipid and glycogen stores serve for metabolic needs during food shortage, while body protein is conserved. The endocrine basis for these changes in the tissue and blood constituents is discussed.     

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.     

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.