A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

Zooplankton in Loch Lomond: perspectives,predation and powan

Published and unpublished accounts of the zooplankton community of Loch Lomond are reviewed. Loch Lomond's zooplankton community is unique amongst those of Scotland's other large lochs. Holopedium gibberum appeared in Loch Lomond in the years between the studies of Slack & Hamilton in the 1950s and zooplankton surveys in the late 1970s.The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyclops leuckarti are described for the mid basin of Loch Lomond. E. gracilis overwinter mainly as adult with variable egg production during their lifespan of 5–8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generation per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton throughout the year, but in low numbers during winter.Zooplankton populations in Loch Lomond are predated by the diverse fish community which includes a facultative planktivore in the powan, Coregonus lavaretus. Powan feed heavily on zooplankton from late spring until late autumn. Powan display selectivity in the prey species taken, in the size distribution and morph types taken within prey species. Zooplankton species, morphs and forms in Loch Lomond tend to reflect this predation.Zoology Department, University of St. AndrewsZoology Department, University of St. Andrews     

Life histories of the powan,Coregonus lavaretus (L.) (Salmonidae,Coregoninae) of Loch Lomond and Loch Eck

Four aspects of the life histories of the two populations of powan Coregonus lavaretus (L.) in Scotland are described: growth (Eck powan are shorter and with greater year to year variance than Lomond); sexual maturation (Eck powan mature younger, but at similar weight to Lomond); spawning (timing in Eck varies, but is consistent in Lomond); and recruitment/mortality (fecundity, sex ratios, and mortality also vary in the short term). Short term differences between the physiological ecology of the populations can be ascribed to the size and topography of the lochs. Long term differences are more difficult to account for, and are more important in that they may signal changes in sustainability. Conservation of powan must be considered in terms of their synecological relationships, not in isolation.     

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.     

The population biology of pike, Esox lucius L., in two gravel pit lakes, with special reference to early life history

The population biology of pike in two gravel pit lakes of contrasting habitat type were studied. The density of pike (1 + and over) in November 1987 in the Main Lake was 7.7 fish ha⁻¹ (19 kg ha⁻¹) and in St Peter's was 71 fish ha'(53 kg ha⁻¹). The age distribution showed that recruitment was consistent in St Peter's but variable in the Main Lake. The main factor causing this difference in recruitment is abundance of aquatic vegetation. Survival up to November 1987 of 0-group pike in the Main Lake was 0.00175% from potential egg deposition, producing 6.6 fish ha⁻¹ (0.83 kg ha⁻¹). In St Peter's survival was 0.00315%, producing 23 fish ha⁻¹ (3.04 kg ha ¹).     

Growth,Reproduction and Condition of Roach (Rutilus rutilus (L.)), Perch (Perca fluviatilis,L.) and Ruffe (Gymnocephalus cernuus (L.)) in Eutrophic Lake Aydat (France)

The growth, reproduction and condition of adults of the three dominant fish species (roach, Rutilus rutilus, (L.); perch, Perca fluviatilis, L. and ruffe, Gymnocephalus cernuus, (L.)) in the eutrophic Lake Aydat were studied over one year cycle. Compared to published data, the growth of R. rutilus and G. cernuus was about average, while that of P. fluviatilis was below average. Comparing to literature, the fecundity of R. rutilus and G. cernuus was low but their oocytes were large. In contrast, P. fluviatilis had a high fecundity but small oocytes. At the end of summer, an abrupt decrease in the condition was recorded only for perch, probably due to stress as a result of environmental conditions. The sex-ratio was in favour of females for the three studied species but, in contrast to G. cernuus, the sex-ratio of R. rutilus and P. fluviatilis increased significantly also with age. It is concluded that Lake Aydat is a more favourable environment for R. rutilus and G. cernuus than for P. fluviatilis.     

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 link between respiratory capacity and changing metabolic demands during growth of northern pike, Esox lucius L.

The relationship between metabolic rate of pike (Y, mgO2) and body weight (X, g) over the range 40–1291 gat 15° C is of the form: Y=aX^b. For resting metabolic rate (V_o2, rest), the scaling coefficient, b , is 0.80 and for maximum metabolic rate measured after exhaustive swimming (V₀₂, max), b is 0.99. Factorial metabolic scope (V₀₂, max/ V₀₂, rest) increases with body weight. Peak postprandial oxygen consumption (V₀₂, ASDA) is a constant multiple of V₀₂ rest for any discrete meal (expressed as % of body weight) up to 10% body weight. V₀₂ASDA after a single meal can utilize the entire metabolic scope (V₀₂, max—V₀₂, rest) of juvenile but not adult pike.     

Seasonal changes in some blood chemistry parameters and in relative liver and gonad weights of pike (Esox lucius L.) from the River Danube

Samples from a natural population of pike (Esox lucius L.) from the River Danube were used in a 12-month study to determine seasonal variations in biochemical parameters of pike blood sera, hepatosomatic index (HSI) and gonadosomatic index (GSI). The ranges of enzyme activities for sample means were: aspartate aminotransferase (ASAT) 252.0–583.8 U 1⁻¹, alanine aminotransferase (ALAT) 4.9–11 -2 U1 and alkaline phosphatase (AP) 39.5–91.8 U1⁻¹. The ranges of other parameters analysed in serum were total protein 27.7–40.1 g 1 ¹, urea 0.57–l.52 mmol 1 ¹ and creatinine 21.2–118.6 μmol 1 ¹. The range of sample means for HSI and GSI were 1.28–4.16 and 0.07–20.2 respectively. Temperature ranged from 4.5 to 23.5°C. The activity of serum AP was positively correlated to water temperature in males only, while urea and creatinine showed a positive correlation to water temperature in individuals of both sexes. GSI was correlated significantly with HSI in females. Total protein reached the lowest values during the spawning period, while creatinine levels depended on both the sex and season.     

Early life characteristics of pike, Esox lucius, in rearing ponds: temporal survival pattern and ontogenetic diet shifts

Survival, biomass and diet of pike, Esox lucius , larvae and juveniles were studied over 3 years by stocking free embryos at a density of six fish m⁻² in 12 drainable outdoor ponds. The ponds were sequentially drained at six larval/juvenile developmental stages, up to a total length (T.L.) of 139 mm. The mean rate of survival at harvest decreased irregularly over time and the highest mortality rates were recorded during the early larval period (13 to 27 mm t.l .) and two intervals of the juvenile period (46 to 99 mm T.L. and 121 to 139 mm t.l .). Mean biomass increased dramatically between 46 mm T.L. (19.8 kg ha⁻¹) and 121 mm T.L. (181.8 kg ha⁻¹) and stabilized between 121 and 139 mm t.l . Sharp increases in the mean weight coefficient of variation were recorded during the early larval period (13 to 27 mm t.l .) and between 74 and 121 mm t.l . (development of cannibalism). Diet breadths were relatively narrow in pike larvae and reached maximum levels in 99 mm t.l . juveniles. Average-sized pike exhibited a sequence of size-dependent shifts from a diet composed primarily (in terms of weight) of micro-crustaceans (at 13 mm t.l .), to chironomid larvae (at 74 to 99 mm t.l .), and finally macrocrustaceans (at 121 to 139 mm t.l .). Cannibalism was detected first among the largest fish at the 74 mm t.l . stage. Between-year diet similarity at various developmental stages was consistently high. In 70 mm t.l . fish harvested from different ponds, we found significant among-pond differences in diet composition; however, similar trends of diet changes in relation to fish size were observed from pond to pond. Our results are discussed in light of existing knowledge of young pike trophic ecology and current aquaculture practices.     

Seasonal dynamics of fatty acid composition in female northern pike (Esox lucius L.)

Seasonal changes in the fatty acid composition of neutral and polar lipids were measured in the ovary, liver, white muscle, and adipopancreatic tissue of northern pike. The role of environmental and physiological factors underlying these changes was evaluated. From late summer (August–September) to winter (January–March), the weight percentage of n-3 polyunsaturated fatty acids (especially 22:6n3) declined significantly in the neutral lipids of all somatic tissues examined. However, large quantities of n-3 polyunsaturated fatty acids accumulated in the recrude cing ovaries during fall and the weight percentage of n-3 polyunsaturated fatty acids in ovary polar lipids also increased significantly. Additionally, the n-3 polyunsaturated fatty acid content of somatic polar lipids increased significantly during fall due to increases in the total polar lipid content of the somatic tissues. This suggests that during fall n-3 polyunsaturated fatty acid are diverted away from somatic neutral lipids and thereby conserved for use in ovary construction and for incorporation into tissue polar lipids. The percentage of n-3 polyunsaturated fatty acid in ovary neutral lipids also declined during fall and early winter, perhaps as an adaptation to conserve these fatty acids for storage in oocyte polar lipids and later incorporation into cellular membranes of the developing embryo. Reductions in the n-3 polyunsaturated fatty acids content of somatic and ovarian neutral lipids during fall were compensated for specifically by increases in the percentage of monounsaturated fatty acids rather than saturated fatty acids. This suggests that the ratio of saturated to unsaturated fatty acids in pike neutral lipid, is regulated physiologically, and hence may influence the physiological functioning of these lipids. During fall and early winter the percentage of saturated fatty acids declined significantly in the polar lipids of all tissues examined. This change was consistent with the known effects of cold acclimation on the fatty acid composition of cellular membranes. As the ovaries were recrudescing from September to January, liver polar lipids exhibited significant decreases in the percentage of total polyunsaturated fatty acids and n-3 polyunsaturated fatty acids and increases in monounsaturated fatty acids, and acquired a fatty acid composition very similar to that of ovary polar lipids. Therefore, seasonal changes in the percentage of polyunsaturated and monounsaturated fatty acids in liver polar lipids probably reflect the liver's role in vitellogenesis rather than the effects of temperature on membrane fatty acid composition. At all times of year, the fatty acid compositions of white muscle and adipopancreatic tissue neutral lipids were very similar, which may indicate a close metabolic relationship between these lipid compartments.Abbreviations AP adipopancreatic - BHT butylated hydroxytoluene - CI confidence interval - EFA essential fatty acids - MUFA monounsaturated fatty acids - NL neutral lipids - PL polar lipids - PUFA polyunsaturated fatty acids - SFA saturated fatty acids     

Direct measurements of metabolism, activity and feeding behaviour of pike, Esox Zucius L., in the wild, by the use of heart rate telemetry

Heart rate telemetry records of up to 5 days duration were obtained from pike living in Lochs Kinord and Davan, Scotland. Applying metabolic rate correlations it was found that mean metabolic rate (R) was 1.5 times standard metabolic rate (R_a), The fish rarely worked near their metabolic limits. Activity metabolism (R_a) was much higher than estimates based on mean swimming speed and comprised up to 10% of R. Most activity metabolism was the result of localized bursts of activity. Less than 10% of activity showed evidence of oxygen debt. Specific Dynamic Action or feeding metabolism (R_f) comprised 15–25% of R. Food intake estimated from heart rate was 1.5% wet body weight day⁻¹, consumed in the form of small items captured during the day and digested during the afternoon and night.     

Evidence of a recent decline in river lamprey Lampetra fluviatilis parasitism of a nationally rare whitefish Coregonus lavaretus: is there a diamond in the ruffe Gymnocephalus cernuus?

Lamprey‐induced scarring of the nationally rare Coregonus lavaretus, a known host of a freshwater‐resident population of European river lamprey Lampetra fluviatilis, was found to have declined precipitously since the establishment of several non‐native fishes in Loch Lomond. Evidence presented in this study points to the possibility that L. fluviatilis in this lake may have altered its trophic ecology in response to the negative impact that non‐native species, in particular ruffe Gymnocephalus cernuus, have had on their favoured host.     

A multivariate morphometric and meristic description of a population of freshwater-feeding river lampreys, Lampetra fluviatilis (L.), from Loch Lomond, Scotland

Adults of a freshwater-feeding population of Lampetra fluviatilis (L.) in Loch Lomond, Scotland, were trapped on their upstream (spawning) migration in the main inflow to the loch, the Endrick Water. These animals could be distinguished from the more typical anadromous upstream migrant L. fluviatilis , from the Endrick Water and the nearby catchment of the River Forth, principally by their smaller total length, greater disc, snout and eye size and much darker pigmentation. These, and other morphometric and meristic characteristics have been compared for populations of L. fluviatilis and Lampetra planeri (Bloch) from the Lomond and Forth catchments using univariate and multivariate statistics. The Endrick Water 'dwarf' L. fluviatilis was found to differ significantly from the other Lampetra studied, in a number of body proportions in addition to those traits mentioned above, and also in mean numbers of trunk myomeres and teeth. These differences are likely to be due to a combination of the effects of genetic isolation, and the short (freshwater) feeding phase of the 'dwarf' L. fluviatilis , which may, therefore, represent the intermediate stage between parasitic and non-parasitic forms in the L. fluviatilis/L. planeri species pair.