Short-term salinity tolerance of northern pike, Esox lucius, fry, related to temperature and size

Abstract  The short-term tolerances of northern pike, Esox lucius L., fry reared in a freshwater hatchery, to salinity were examined in the laboratory. Survival of two size groups of pike fry (mean length 21 ± 2 mm SD and 37 ± 4 mm SD) was examined over 72- to 96-h periods at 9–14 ppt salinity in combination with temperatures of 10, 14 and 18 °C. A parametric survival model found a significant correlation between survival of pike fry and temperature and salinity, respectively. L _C50 values after 72 h were between 11.2 and 12.2 ppt, being lowest at 10 °C. Pike fry did not survive more than 13 ppt. Mortality at 12 ppt was significantly faster at 18 °C than 10 or 14 °C. Moreover, mortality was higher and faster for large than for small pike fry at 12 ppt and 14 °C. These results imply that pike raised in fresh water can survive stocking into brackish waters below 11 ppt at least for a short time.     

The desaturation and elongation of 14C-labelled polyunsaturated fatty acids by pike (Esox lucius L.) in vivo

To examine the ability of pike (Esox lucius L.) to modify exogenous PUFA by desaturation and elongation, ¹⁴C-labelled 18:2(n-6), 18:3(n-3), 20:4(n-6) and 20:5(n-3) were injected intraperitoneally and the distribution of radioactivity in tissue lipid classes and liver PUFA measured. In all tissues examined, radioactivity from all ¹⁴C-PUFA was recovered in many classes of acyl lipids and the level of recovery generally reflected the relative abundance of the lipid classes. Triacylglycerols, CGP and EGP usually contained high levels of all incorporated ¹⁴C-PUFA. PI contained higher levels of radioactivity from ¹⁴C-20:4(n-6) than from other injected substrates. In liver lipid, the 6 desaturation products of ¹⁴C-18:2(n-6) and ¹⁴C-18:3(n-3) contained no measurable radioactivity although the elongation products of the 6 desaturation products were labelled, as were the direct elongation products of these injected substrates. No radioactivity from ¹⁴C-18:2(n-6) or ¹⁴C-18:3(n-3) was detected in C₂₀ or C₂₂ products of 5 and 4 desaturation. Almost all radioactivity from injected ¹⁴C-20:4(n-6) was recovered in this PUFA. Of the total radioactivity from ¹⁴C-20:5(n-3) incorporated into liver lipid, 7% was present as 24:5 and 16.4% was recovered in hexaenoic fatty acids. In liver, 24:5(n-3) and 24:6(n-3) each accounted for 1% of the mass of total fatty acids and were located almost exclusively in triacylglycerols. The presence of radioactivity in these C₂₄ PUFA suggests that in pike the synthesis of 22:6(n-3) from 20:5(n-3) may proceed without 4 desaturase via the pathway which involves chain shortening of 24:6(n-3). It is concluded that under the circumstances employed in this study pike, do not exhibit 5 desaturase activity and are unable to synthesize 20:4(n-6) and 20:5(n-3) from 18:2(n-6) and 18:3(n-3), respectively. This suggests that pike may require 20:4(n-6) and 20:5(n-3) preformed in the diet.Abbreviations CGP choline glycerophospholipids - CL cardiolipin - EGP ethanolamine glycerophospholipids - PG phosphatidylglycerol - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acids - SM sphingomyelin - TLC thin-layer chromatography     

Changes in lipid class and fatty acid composition during development in pike (Esox lucius L) eggs and larvae

To establish the changes which occur during embryogenesis and early larval development, eggs, yolk sac larvae and swim-up larvae of pike were examined for lipid class and fatty acid composition. At a water temperature of 15.5°C, the embryonic phase was short (6 days) and characterized by a 41.3% decline in the lipid content of eggs, accompanied by large reductions in the amount of phosphatidylcholine (41.4% decrease), sterol esters and triacylglycerols (respectively a 41.2% decrease and a 58.1% decrease), but not phosphatidylethanolamine which increased markedly (35.6%). By the time of yolk sac absorption (7 to 11 days after fertilization) the larvae remained inactive and a limited utilization of lipids was observed. Yolk sac phosphatidylcholine was selectively incorporated into larval bodies while the levels of other lipid classes remained unchanged in the yolk. When the swim bladder was filled and the swimming stage was reached (11 days to 13 days af), the yolk was completely depleted and yolk phosphatidylcholine together with yolk triacylglycerols were catabolised. Yolk phosphatidylethanolamine and yolk sterol esters were partly incorporated into the body lipids. In the subsequent swim-up larval stage (13 to 15 days af), a steady decrease in lipids was observed (41.6%). Fluctuations in the levels of polyunsaturated fatty acids, monounsaturated fatty acids or saturated fatty acids examined from eggs or larvae were consistent with changes in lipid classes during pike development. During yolk sac absorption, pike incorporated yolk PUFA released on hydrolysis of phosphatidylcholine into the larval body. The results are discussed with reference to water temperature and in relation to the ontogenic and ecological context of pike development. This revised version was published online in July 2006 with corrections to the Cover Date.     

High salinity tolerance in eggs and fry of a brackish Esox lucius population

Abstract Knowledge on the biology and physiology of pike, Esox lucius L., populations inhabiting saline environments is scarce. An experimental setup was used to examine egg development and fry behaviour and growth under varying salinity levels in a brackish‐water pike population from the western Baltic Sea. Eggs and fry developed at 8.5 psu, which is higher than hitherto reported for other populations. Fry exhibited stress behaviour and reduced growth when subjected to salinities above 13 psu. This indicates that early life stages of E. lucius tolerate ambient salinity conditions equivalent to the natural environment in its nursery area in the Stege Nor lagoon. The population should therefore not be dependent on access to freshwater environments during spawning. However, the results also suggest that the population’s natural environment is on the margin of its physiological capacity. The results have significance for management of brackish‐water E. lucius populations, e.g. in relation to stocking strategies.     

Annual movement of adult pike (Esox lucius L.) in a lowland river

Abstract –  The movement of ten radio-tagged adult pikes (57–113 cm) in the River Gudenå, Denmark, was investigated from September 1998 to September 1999. The movements of pike were characterised by long resident periods in the submergent vegetation, interrupted by short excursions to nearby areas. Two periods with more intense movement were observed; one period during early winter; and one period during spring from mid-March to mid-May. The increased movement during early winter may have been initiated by a slight temperature increase at this time, whereas the increased movement during spring coincided with the spawning of pike. Despite suitable spawning areas nearby the areas where pike resided most of the year, several pike, mainly females, migrated to distant localities during spring.     

Investigation on fecundity, follicles and free embryo size of pond-reared pike (Esox lucius) of different age and size

The purpose of the present study is to investigate the gonadosomatic index (GSI %), the absolute and relative fecundity of one-year-old pike weighing over 400 g and at the same time to study the dependence between the egg size and the size, behavior and vitality of the free embryos obtained from one- and two-year-old spawners. The study involved two weight groups of females, differing in age and body weight and length—one-year-old (W = 514 g, SL = 36.1 cm) and two-year-old matured pike (W = 1454 g, SL = 49.3 cm). Ovary samples were fixed and egg follicles containing maturing oocytes counted and weight. The weight and length of the free embryos from semi-artificial spawning were measured. The results showed that, when raising this species under farmed conditions, more than 40% (in rarer cases 90%) of one-year-old pike females reached over 400 g and 35 cm (SL) and reached puberty. Absolute fecundity of 15,030 follicles (30 follicles per gram body weight) was observed; the GSI was nearly 15% and the follicle weight reached 3.7 mg. This data differs significantly from that obtained from the larger two-year-old fishes: absolute fecundity 41,363 follicles (28 follicles per gram body weight), GSI nearly 20%, follicle weight 5.8 mg. Results showed that the different follicle size determines the free-embryo size. A positive linear correlation was found between the egg follicle weight and the free-embryos weight (r = 0.7143). The free embryos obtain from the one- and two-year-old spawners differed significantly both in terms of their weight (7.13 mg against 10.61 mg) and total length (0.81 cm against 0.97 cm), the differences being 1.5- and 1.2-fold, respectively.     

Patterns of movement of adult northern pike (Esox lucius L.) in a regulated river

Abstract –  We performed a tagging study on one of the spawning populations of northern pike ( Esox lucius L.) of the River Kajaaninjoki in Finland. Northern pike is the main predator in many lakes and rivers in the northern hemisphere. Previous tagging studies have shown a general tendency to sedentary behaviour by pike. Whether individuals in a fish population adapt a sedentary or moving strategy may affect population persistence. To study if the spawning population consists of sedentary or moving individuals and the pattern of movements, we tagged 40 pike with radio transmitters and followed them from May 2002 to June 2003. Pike were caught and tagged during the spawning season in the mouth of the River Kajaaninjoki which flows into one of the largest lakes in Finland, Lake Oulujärvi. Our results suggest that the pike spawning population consisted of sedentary pike ( N  = 16) dwelling the whole year in the river, and moving pike ( N  = 24) which moved to Lake Oulujärvi after the spawning period. Pike exhibited homing behaviour, as most of the migrating pike returned to the same spawning area in the following year. Large pike had a higher movement rate than small pike during the summer and seasonally the movement rate was lowest during the spring and highest during the summer.     

Effect of EPA/DHA ratios on the growth and survival of Galaxias maculatus (Jenyns, 1842) larvae reared under different salinity regimes

Despite the importance of certain highly unsaturated fatty acids in osmotic regulation, few studies have been addressed to determine the essential fatty acid requirements for a given species cultured under different salinities. As Galaxias maculatus is a diadromic species, the present study aimed to determine the effect of salinity on the optimum dietary EPA/docosahexaenoic (DHA) ratio for survival and growth during the larval stages. Larvae were fed for 20 days with rotifers containing two different EPA/DHA ratios (low: 0.64 and high: 2.18) at three different salinities (0, 10 and 15 g L^?1). The results of this study showed a marked effect of water salinity on larval dietary lipid utilization in G. maculatus larvae. These results suggested that G. maculatus larvae reared at higher salinities may have a higher dietary requirement for DHA, whereas larvae reared at 0‰ showed higher requirements for EPA. The overall results of the present study indicate that even small changes in salinity can determine the optimum dietary EPA/DHA ratio and the quantitative essential fatty requirements of fish. This may have important repercussions and affect the rearing performance of G. maculatus cultured under different salinities.     

Changing of fat content and fatty acid profile of reared pike (Esox lucius) fed two different diets

Fat content and fatty acid profile of two pike yearling groups grown on two different diets were compared. The groups originated from culture on artificial feed. One group (cultured pike fed first pellet then prey‐fish (PF)) was fed with natural food, live prey‐fish, while the other one (cultured pike fed exclusively pellet (PP)) by trout feed through a 3‐month experimental period. Growth of pike was lower with PP than with PF. The trout feed resulted in an increase of the fat content of fillet and the formation of abdominal fat depots. Feeding of natural food decreased the fat content. The proportion of the saturated fatty acids in fillet was higher in the (PF) group. The n‐6 fatty acids (arachidonic C20:4n‐6 and docosatetraenic C22:4n‐6 acids) were lowest in PP‐fed pike. Regarding total n‐3 fatty acids ratio there was no significant difference between the groups, but the level of α‐linolenic (C:18:3n‐3) acid showed significant difference among groups.     

Protracted spawning of St Lawrence River northern pike (Esox lucius): simulated effects on survival, growth, and production

Abstract –  An individual-based early life history model demonstrated that the timing and distribution of St Lawrence River northern pike ( Esox lucius ) spawning could affect subsequent young-of-year (YOY) production during nursery and influence year-class formation. Three different spawning patterns have emerged from empirical studies, where egg deposition occurred along the entire littoral gradient beginning in seasonally flooded emergent habitats in tributaries, progressing to submerged aquatic vegetation in shallow bays, and ending in deep water littoral habitats (up to 6 m). The spawning period is protracted, and typically lasts 6–8 weeks due to the presence of a strong thermal gradient. The model used temperature as the driving variable to predict egg abundance, stage-specific development, growth, survival, and ultimately relative production of YOY northern pike within 1-ha plots representative of the three habitats. Earlier spawning (mean 21 days) and higher mean daily survival and growth yielded higher YOY net production for tributaries (mean = 3095.4 g ha⁻¹, SD = 2028.6) relative to the shallow bay habitat (202.5 g ha⁻¹, SD = 125.7). In contrast, deep littoral habitat represented an ecological sink with little production (<0.9 g ha⁻¹). The results demonstrate the importance of the linkage between spawning and nursery processes in determining reproductive success.     

不同密度白斑狗鱼受精卵孵化率及初孵仔鱼成活率比较

2009年4-5月在河北省赞皇县正和水产良种有限公司,进行了白斑狗鱼规模化全人工繁育技术研究。对不同密度受精卵孵化率及初孵仔鱼成活率进行了比较研究,结果表明:受精卵孵化密度在8 000~15 000粒/槽较为适宜,最佳密度为10 000~13 000粒/槽;初孵仔鱼培育密度10 000~15 000尾/m3水体较为适宜,最佳密度为11 000~13 000尾/m3水体。     

Food consumption of northern pike (Esox lucius L.), estimated with a bioenergetics model

Abstract– A bioenergetics model was used to estimate the food consumption of northern pike ( Esox lucius L.) in two lakes in northeastern Finland, and the results compared with those obtained by a method based on stomach contents and gastric evacuation rates. The annual specific food consumption was 7–5 g per one gram pike for one- and two-year-old pike, and 4–3 g g⁻¹ in age groups 3–6 years old, according to the bioenergetics model. The proportion of ingested food used for growth was 10–30%, and was highest in the youngest age groups. The food consumption rates estimated by the stomach contents method were considerably lower, only about half those produced by the bioenergetics model. The method based on stomach contents tends to underestimate the food consumption. The bioenergetics model was considered more valid for estimating food consumption, but some of the parameter values for northern pike may differ in populations from different latitudes. According to a sensitivity analysis, the food consumption estimate of the bioenergetics model was most sensitive to parameters in the allometric function for respiration.     

Movements of pike, Esox lucius, in Lower Lough Erne, determined by mark–recapture between 1994 and 2000

Abstract Between 1994 and 1997, 508 pike, Esox lucius L., were tagged in Lower Lough Erne (LLE), Northern Ireland. By August 2000, 79 of these fish were recaptured. Ten of 27 pike recaptured and released a second time were then captured a third time. Distance from tagging to recapture site ranged from 0 to 16 km, with most recaptures within 10 km. Pike dispersed widely after spawning, an observation supported by netting survey data, and tended to return to the same spawning sites year after year. The usefulness of designated sanctuary areas free of commercial fishing, intended to maintain a stock of pike reserved for angling was evaluated. To protect angling stocks of pike from commercial fishing, sanctuary areas should be somewhat larger than at present.     

The Effect of Thermal Treatment Method on Fatty Acid Composition in Northern Pike (Esox lucius) Fillets

The aim of the present study was to investigate the effect of thermal treatment methods, such as microwave cooking, steaming, and shallow pan-frying on fatty acids composition in northern pike fillets. All methods of thermal treatment increased fat content in the fillets. Microwave cooking decreased the proportion of saturated fatty acids and increased the proportion of total, n-3, and n-6 polyunsaturated fatty acids as compared with fresh fillets. Steam cooking did not affect the proportion of saturated, monounsaturated, and polyunsaturated fatty acids, whereas pan-frying significantly increased the proportion of monounsaturated and n-6 polyunsaturated fatty acids. All cooked fillets, regardless of the thermal treatment used, had acceptable n–6/n–3 ratio; however, microwave cooking enabled fish products to obtain more beneficial n-6/n-3 ratio than frying. Due to high polyunsaturated fatty acids content and low n-6/n-3 ratio, microwave cooking may be recommended for preparing wild pike fillets in households.     

Spatial behaviour of young-of-the-year northern pike (Esox lucius L.) in a temporarily flooded nursery area

Abstract –  Unlike adult northern pike ( Esox lucius ), small-bodied young-of-the-year (YOY) individuals cannot be tracked by conventional telemetry, and virtually no data exist on their spatial behaviour. Here, we monitored 192 individuals released into a nursery area (0.47 ha, subdivided into 253 cells of 4 m × 5 m) that dried out progressively using a portable passive integrated transponder detector. Among them, 66 spent more than 5 days in the nursery area and were localised at least twice, allowing spatial behaviour analyses. The mean radial distance moved averaged 14.3 m (±8.4 SD, range 2.2–41.0) and the average daily movement was 8.0 m·day⁻¹ (±5.3 SD, range 0.6–31.1). Pike abundance in a cell significantly correlated with the abundance observed in adjacent cells within 32 m, confirming a patchy distribution. A selective use of the deepest area was measured while no effect of vegetation cover was observed at the cell scale. The existence of YOY pike aggregations and the positive correlation between water depth and their spatial distribution might, however, facilitate predation and/or cannibalism during this critical period. This also suggests that the choice of release habitats requires particular attention during restocking procedures.     

Daily food intakes and optimal food concentrations for red king crab (Paralithodes camtschaticus) larvae fed Artemia nauplii under laboratory conditions

Daily food intakes, optimal feeding regimes and food concentrations for laboratory reared Paralithodes camtschaticus (Tilesius, 1815) larvae were investigated. Artemia nauplii hatched at standard conditions were used as food. Daily food intakes of zoeae I–IV at 7–8 °C comprised 11.3, 22.4, 33.2, and 41.8 nauplii individuals (ind)^?1 day^?1, respectively, taking into account that wet weight of Artemia nauplii used for the experiments constituted 0.026 mg, dry weight 0.0042 mg. Optimal initial Artemia nauplii concentrations for feeding zoeae I–IV was determined as 400–600, 600–800, 800–1000 and 1000–1200 nauplii L^?1 respectively. Recommendations on using Artemia nauplii as food for red king crab larvae were outlined on the basis of experimental results. Growth, development and survival rates of zoeae I–IV reared in recycling water system at 7–8 °C and fed Artemia nauplii according to these recommendations were described.     

Effects of salinity on the fatty acid compositions of total lipid and individual glycerophospholipid classes of Atlantic salmon (Salmo salar) and turbot (Scophthalmus maximus) cells in culture

Cells from a relatively stenohaline marine species, turbot (Scophthalmus maximus) (TF) and an anadromous species, Atlantic salmon (AS) were cultured in media supplemented with NaCl to produce OPs varying from 300 to 500 mOsm kg^–1 and the direct effects of OP (salinity) on the fatty acid compositions of the main glycerophospholipid classes were determined. The most dramatic effects of salinity on total lipid fatty acids were observed in polyunsaturated fatty acids (PUFA) in TF cells. There was a graded decrease in the percentage of 18:2n-9, and consequently total n-9 PUFA, and concomitantly increased percentages of both total n-3 and n-6 PUFA with increasing salinity. The increased n-3 and n-6 PUFA was due to significantly increased percentages of the major fatty acids in each of these groups, namely 22:6n-3 and 20:4n-6, respectively. The reciprocal changes in n-9 PUFA and n-3/n-6 PUFA in TF cell total lipid resulted in the percentage of total PUFA not being significantly affected by changes in salinity. The graded decrease in 18:2n-9 with increasing salinity in TF cells was observed in all the major glycerophospholipids but especially PE, PI and PS. Increasing salinity resulted in graded increases in the percentages of 22:6n-3 in PE and PS in TF cells. The quantitatively greatest increase in the percentage of n-6 PUFA in TF cells occurred with 20:4n-6 in PC, PE and PL. There were less significant changes in the fatty acid compositions of glycerophospholipids in AS cells. However, the proportion of total n-3 + n-6 PUFA in PE varied reciprocally with the proportion of dimethylacetals in response to salinity. Similar reciprocal changes between fatty acids in response to salinity were also evident in the quantitatively more minor glycerophospholipids PS and Pl. In PS, the percentage of 22:6n-3 was significantly lower at 400 mOsm kg^–1 whereas the proportion of total monoenes was significantly higher at that salinity. A similar inverse relationship between total monoenes and 20:4n-6 (and, to a lesser extent total saturates) in response to salinity was noted in PI. The results show that environmental salinity, without whole-body physiological stimuli, has direct effects on the fatty acid composition of major glycerophospholipid classes in fish cells and that these effects differ in cells from different fish speciesAbbreviations ANOVA analysis of variance - BHT butylated hydroxytoluene - BSA bovine serum albumin - DMA dimethylacetals - EMEM Eagle's minimal essential medium - FCS fetal calf serum - GC gas chromatography - HBSS Hank's balanced salt solution (without Ca²⁺ and Mg²⁺) - OP osmotic pressure - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid - TLC thin-layer chromatography     

Effects of salinity on growth and mortality of migratory and resident forms of Eurasian perch in the Baltic Sea

Abstract – In the coastal areas of the Baltic Sea, there are two forms of perch (Perca fluviatilis). One of the forms is migratory and spawns in streams entering the Baltic Sea. The other form is resident and spawns in brackish water. Both forms utilise the coastal habitat for foraging. We examined the spawning success of the two forms in fresh and brackish water (7‰, equal to salinity in the south Baltic Sea). The experiments showed that hatching success was equally high in freshwater and in brackish water despite female origin. The survival of yellow‐sac and free swimming fry was significantly reduced in brackish water, which was independent if the fish was of migratory or brackish resident origin. Further, growth rate of perch fry was severely reduced in brackish water. The results indicate that perch has not developed any tolerance to brackish water in the young life stages. The migratory life strategy of perch can thus be explained by higher survival of fry in freshwater.     

Northern pike (Esox lucius) growth and mortality in a northern Ontario river compared with that in lakes: influence of flow

Abstract –  We measured the growth and mortality characteristics of northern pike ( Esox lucius ) in a northern Ontario river and examined the influence of flow on these characteristics by comparing our measurements with those estimated for a lake at the same latitude based on published studies. Pike ranged in total length from 229 to 784 mm, in mass from 70 to 4250 g, and in age from 1 to 10 years. The population showed a preponderance of 2–5-year olds, with few fish surviving beyond 7 years of age. Growth, in terms of length increase, was similar to that reported for circumpolar populations. Mean total length at 5 years of age was 577 mm, growth rate of young adults was 62.5 mm year⁻¹, growth was isometric, longevity was 10 years of age, and the adult annual mortality rate was 49%. Growth and mortality characteristics of this riverine population were similar to those estimated for a lacustrine population at the same latitude. Flow thus had little measurable effect on the growth or mortality of pike possibly because of the overwhelming effect of other abiotic variables such as temperature, length of growing season and productivity. Consequently, growth characteristics of lacustrine populations can be used to assess the health and condition of riverine populations.     

Comparative activity and stability under salinity conditions of different antimicrobial peptides isolated from aquatic animals

This study reports the in vitro activity of six antimicrobial peptides (AMPs) produced by aquatic animals (most marine invertebrates): tachyplesin (Tach), magainin (Mag), clavanin (Clav), penaeidin (Pen), mytilin (Myt) and antilipopolysaccharide factor (ALF) against marine vibrios, filamentous fungi and yeast. Their stability under salinity conditions and seawater was also examined. The results showed that Mag, Myt and especially Tach and ALF (minimum inhibitory concentration<1.5 μM) had a potent activity against all tested vibrio species, whereas Clav and Pen were ineffective (up to 50 μM). With respect to the antifungal activity, each AMP had a different potency according to the fungal species. In general terms, Tach was the most potent peptide, followed by Mag. Interestingly, Tach, Myt and ALF had a significant effect on the filamentous fungus Fusarium solani that could be pathogenic to marine organisms. All AMPs had a tendency to decrease or lose their activity at high salinity (>225 mM NaCl). Tach and Myt were the most stable peptides, maintaining significant activity under seawater salinity (450 mM). Curiously, all peptides lost their effect under seawater conditions. The results suggest that Tach, ALF and Myt are the most promising candidates for potential therapeutic use in farmed-marine species, because all have a significant and broad antimicrobial activity maintained at high salinity.