Larval Northern Pike Research Articles

Initial diet influences future development paths of gut microbiota in larval northern pike (Esox lucius)

Initial diet influences future development paths of gut microbiota in larval northern pike (Esox lucius)

Effects of temperature on somatic growth, otolith growth, and uncoupling in the otolith to fish size relationship of larval northern pike, Esox lucius L

Verifying the link between somatic and otolith growth is crucial for a number of analyses that provide data on the ecology of early life stages of fish. In the current study, sagittal and lapillar otoliths were extracted from larval northern pike (n = 720) that were reared from eggs in RAS systems at three temperatures (10 °C, 15 °C, and 22 °C) for 28 days. The growth rate (SL at age) of larval northern pike was significantly dependent on rearing temperature with the highest rate observed at 22 °C (0.83 mm·d−1), a lower rate at 15 °C (0.48 mm·d−1), and the lowest at 10 °C (0.25 mm·d−1). The maximum value of growth observed for an individual larvae at a certain age was 1.28 mm·d−1. The higher somatic growth rate at higher temperatures was followed by faster lapillus and sagitta linear growth rates. Positive relationships between otolith growth and somatic growth were noted not only among temperatures but also within given temperatures. The sizes of lapilli and sagittae were strongly correlated with fish size, but both somatic growth and temperature had a statistically significant effect on those relationships. Magnitude of this phenomenon was however fish size dependent. We concluded that larval northern pike otoliths (both sagittae and lapilli) are a reliable source of information on somatic growth, and they can be used for increment trajectory width analysis and marginal otolith increment width analysis. However, if growth back-calculation is to be employed, it is recommended to consider the somatic growth and temperature effect on the fish size-otolith size relationship.

Improving Habitat Connectivity in a Typha-Dominated Wetland Shows Increased Larval Northern Pike Survival

A decline in northern pike (Esox lucius) abundance in the upper St. Lawrence River is thought to be related to hybrid cattail invasion and disruption of natural water-level periodicity leading to spawning and nursery habitat degradation. Channel-connectivity and spawning-pool excavations were implemented in a tributary to the upper St. Lawrence River to enhance spawning and nursery site complexity. We assessed the effects of excavations on pike by comparing percent survival (from advanced larvae to fall emigration), water quality factors, and larval diets at excavated and non-excavated sites. Lab-reared pike, 16 days post-hatch and 14 mm in length, were released at three site types: non-excavated, spawning pool, and channel. Percent survival in channels and spawning pools after a minimum of 26 days was nearly identical (2.4%), and greater than non-excavated sites (0.13%). Spawning pools displayed higher water temperatures and dissolved-oxygen concentrations than either channel or non-excavated sites. Larvae primarily consumed zooplankton and diets of larvae from spawning pools and non-excavated sites were similar, whereas larvae in channels consumed different taxa. Differences in diet were not reflected in survival, suggesting larvae were not prey-limited. Observed differences in percent survival among sites demonstrates created spawning pool and channel-connectivity sites enhanced conditions for pike.

Prey selection by larval northern pike (Esox lucius) exposed to different zooplankton assemblages representing seasonally flooded wetland and nearshore bay habitats

AbstractA prey selection experiment was designed to investigate whether northern pike larvae, at swim‐up and advanced stages, select similar zooplankton prey in seasonally flooded wetlands and nearshore littoral zones, which represent primary St. Lawrence River northern pike spawning habitats. At first exogenous feeding, naïve swim‐up larvae exposed to both wetland and nearshore zooplankton were generalist consumers, feeding primarily on cyclopoid copepods and small cladocerans. No positive selection was observed for any prey taxa. Advanced larvae began to exhibit positive selection for large cladocerans. Significantly larger‐sized prey were consumed by advanced larvae given wetland vs. nearshore zooplankton. Large cladocerans made up a greater proportion of the assemblage originating from seasonally flooded wetlands vs. nearshore habitats, and may explain the difference in size selectivity. Our laboratory experiment suggests pike hatched in wetland environments have greater access to preferred, large cladoceran prey, and differences in spatial and temporal spawning distributions may have important implications for zooplankton availability and hence food consumption during the critical larval period.

Daily deposition of growth increments in sagittae and lapilli of laboratory-reared larval northern pike (Esox lucius)

Daily deposition of growth increments in sagittae and lapilli of laboratory-reared larval northern pike (Esox lucius)

Effect of Preservation in Formalin and Alcohol on the Growth Rate Estimates of Larval Northern Pike

AbstractBody length measurements and growth rate (GR) analysis are important steps in research on the ecology of early development stages of fish. In order to obtain accurate results, the lengths of field‐collected and preserved larvae must be corrected for shrinkage. Northern Pike Esox lucius larvae were kept in the laboratory in freshwater conditions (300‐L tank; temperature = 16°C), where they were fed six times a day ad libitum with aquaculture feed. Every 3 d over a period of 30 d, a subsample of approximately 30 larvae was collected, measured, and placed in separate vials in 96% alcohol and 4% formalin. All of the larvae (8.8–34 mm SL; n = 276) were measured again after 90 d of preservation. The shrinkage ranged from 0% to 11.6%, averaging 3.42% in alcohol (n = 134) and 3.74% in formalin (n = 139). The difference was not statistically significant. In both preservatives, the relative shrinkage (%) was higher for small fish than for large fish. The length correction for 8–34‐mm SL fish in both alcohol and formalin should be done by adding 0.7 mm to the length measured after preservation. Shrinkage did not affect fish GRs estimated based on linear regression fitted to size‐at‐age data (0.645 mm/d for unpreserved larvae and 0.650 mm/d for preserved larvae). In the opposite case, when growth was estimated as mean GR between hatching and sampling, the shrinkage effect was significant: the mean GR was 0.604 mm/d for unpreserved larvae and 0.558 mm/d for preserved larvae. The presented shrinkage correction formula allows for obtaining accurate length and GR data for larval Northern Pike that should lead to conclusions that credibly support undertaking appropriate management strategies.

Effects of Age at Treatment on Oxytetracycline Mark Formation in Larval Northern Pike

AbstractOxytetracycline (OTC) immersion treatments were evaluated at the Waterville State Fish Hatchery (Waterville, Minnesota) for producing fluorescent marks on larval Northern Pike Esox lucius otoliths. A pilot marking trial conducted with 7‐d‐posthatch (dph) larvae resulted in poor mark efficacy and prompted further investigation on the treatment of younger larvae and modification of the treatment by use of osmotic induction to promote better mark formation. Northern Pike treated within 24 h post‐hatch had significantly higher mark efficacies and marked otolith intensities than did Northern Pike treated at later life stages. Similar to the pilot marking trial, immersion of 7‐dph fry in OTC solution resulted in poor mark efficacy, in which only 38% of the inspected fry possessed visible marks and most of the marks that were visible appeared faint. Simple immersion of newly hatched fry in OTC solution resulted in 91% marking success, and 65% of the visible marks appeared either clear or intense. The poorer mark efficacy on 7‐dph fry suggests that differences in mark formation were more dependent on contemporaneous physiological processes than on otolith size. Osmotic induction prior to OTC immersion had a much weaker effect on mark intensity than did age‐class of treatment in the study.Received November 12, 2013; accepted March 30, 2014

Vegetative substrates used by larval northern pike in Rainy and Kabetogama Lakes, Minnesota

AbstractOur objective was to identify characteristics of aquatic vegetative communities used as larval northern pike nursery habitat in Rainy and Kabetogama lakes, glacial shield reservoirs in northern Minnesota. Quatrefoil light traps fished at night were used to sample larval northern pike in 11 potential nursery areas. Larval northern pike were most commonly sampled among floating‐leaf burreed Sparganium fluctuans, common burreed Sparganium eurycarpum, sedges Carex spp., hybrid cattail Typha × glauca and wild rice Zizania palustris. A negative binomial model of light‐trap catches using the presence/absence data for 2012 from all 11 bays included water elevation and the presence of cattail as significant variables. Ultimately, the species of vegetation may not be as important as the physical quality or form of the vegetation in supplying feeding and hiding cover. The aquatic plant species and structural forms encountered by larval northern pike suggest they use nearly any vegetated cover available in early spring. Water‐level regulations that change availability of aquatic vegetation are likely to influence recruitment of northern pike to larger sizes.

Fluence Rate or Cumulative Dose? Vulnerability of Larval Northern Pike (Esox lucius) to Ultraviolet Radiation

Newly hatched larvae of northern pike were exposed in the laboratory to four fluence rates of ultraviolet radiation (UVR; 290-400 nm) over three different time periods, resulting in total doses ranging from 3.0 +/- 0.2 to 63.0 +/- 4.4 kJ.m(-2). Mortality and behavior of the larvae were followed for 8-12 days, and growth measured at the end of the experiment. Also, the principle of reciprocity-that the UVR-induced mortality depends on the cumulative dose, independent of fluence rate-was tested. Fluence rates higher than 1480 +/- 150 mW.m(-2) caused mortality and growth retardation. The highest fluence rate (3040 +/- 210 mW.m(-2)) caused 100% mortality in 5 days. All fluence rates caused behavioral disorders, which led to death at fluence rates higher than 1480 mW.m(-2). Reciprocity failure occurred with the lowest and highest dose (550 +/- 45 and 3040 +/- 210 mW.m(-2), respectively). The results show that fluence rate is of primary importance when assessing the UVR-related risk.

Larval Deformities Associated with Selenium Accumulation in Northern Pike (Esox lucius) Exposed to Metal Mining Effluent

The objective of this study was to investigate selenium toxicosis in larval northern pike (Esox lucius) originating from reproductively mature pike collected downstream of a uranium milling operation in northern Saskatchewan, Canada. Eggs were obtained from female pike collected from a reference site and three sites representing an exposure gradient (approximately 2, 10, and 15 km downstream of effluent discharge). Embryos were incubated following a two-way (crossover) analysis of variance experimental design that allowed discrimination between effects due to maternal transfer to eggs and effects due to site water exposure in the developing embryos. The major finding of this study was a significant increase in the frequencies of individual deformities (skeletal curvatures, craniofacial deformities, and fin deformities) and edema in fry originating from high and medium exposure site females (mean selenium concentrations of 48.23 and 31.28 microg/g egg dry weight and 38.27 and 16.58 microg/g muscle dry weight, respectively) compared to reference site females. Selenium concentrations resulting in a 20% increase in total deformities above background levels (EC20S) were 33.55 and 21.54 micro/g dry weight in eggs and muscle, respectively. Mathematical conversion of the egg- and muscle-derived relationships to whole body selenium levels resulted in similar EC20S of 15.56 and 17.72 microg/g dry weight, respectively. These relationships between tissue selenium levels and larval deformities suggest that northern pike are within the same range of sensitivity to selenium as the majority of warm water (e.g., centrarchids and cyprinids) and cold water (e.g., salmonids) fish species studied to date.

Size of Larval Northern Pike Emigrating from Spawning Wetlands

ABSTRACT We collected larval northern pike (Esox lucius) in spawning wetlands and adjacent deepwater habitat during the springs of 1993 and 1994. Larval northern pike began to emigrate from spawning wetlands at sizes as small as 14.0 mm TL; however, they remained in close proximity to spawning wetlands until reaching sizes of 50 mm TL or greater. The initial emigration began before larvae became cannibalistic, and larger larvae emigrated before smaller ones indicating that intraspecific aggression probably does not play a role in this stage of emigration. Samples later in the spring indicated that some larvae either delayed emigration or returned to deeper parts of spawning wetlands. Transitional habitats may be important for survival of young of the year northern pike.

Development of cannibalism in larval northern pike, Esox lucius (Esocidae)

The development of cannibalism of northern pike (Esox lucius) larvae was studied under controlled conditions. Pike larvae were reared in six glass, 50–1 aquaria at three stocking densities: 440, 2 200 and 4 400 larvae per aquarium. Fish were fed ad libitum with Artemia nauplii and sieved Zooplankton. After 4, 8 or 12 days of rearing, pike larvae were anaesthetised and measured for total length (TL) and body weight (BW). Lowest survival and fish size were noted at the highest stocking density. The frequency of all cannibalistic attacks decreased in the order: highest > middle > lowest density; the frequency of successful attacks (expressed as the number of injured sibling fish) decreased, however, in opposite order.

Density, Size, and Foods of Larval Northern Pike in Natural and Artificial Wetlands

Larval northern pike Esox lucius were sampled in natural and artificial wetlands associated with Conesus Lake, New York, on 25 April, 8 May, and 26 May 1992. Larval northern pike population densities declined significantly between the first (25 April) and second (8 May) sampling periods, indicating mortality or emigration from the wetlands; only two northern pike were captured on 26 May. Larval northern pike population densities were higher in artificial wetlands on 25 April, but on 8 May no difference could be detected. Mean total length of larvae was greater in artificial wetlands on 25 April and 8 May. Larval northern pike began feeding at approximately 15 mm total length. No difference in number of food items eaten was detected between natural and artificial wetlands; however, percentage of copepods, the taxa most commonly eaten, was higher in northern pike stomachs from natural wetlands. Cannibalism was observed in 1 of the 76 stomachs examined and constituted the only vertebrate food item found. Artificial wetlands were comparable or superior to natural wetlands as northern pike spawning and rearing habitat.

System for Maintaining Sediment Suspensions during Larval Fish Studies

Abstract A new system was developed for maintaining suspensions of inorganic solids during laboratory studies on early life stages of fish. Microfine bentonite was successfully held in suspension in specially constructed units during a 21-d fishless test, a 28-d experiment with juvenile green sunfish (Lepomis cyanellus), and four shorter experiments (5–9 d) with four species of larval fishes, white sucker (Catostomus commersoni), northern pike (Esox lucius), channel catfish (Ictalurus punctatus), and walleye (Stizostedion vitreum). Each experiment on larval fish was conducted until the yolk-sac had been absorbed. Concentrations of bentonite ranged from 0 to 728 mg/L. Each unit consisted of a holding chamber set in a stainless steel bowl and two submersible pumps that recirculated the suspension. Turbidity readings remained nearly constant throughout each experiment. Because the turbidity of suspensions was well correlated with bentonite concentration (r 2–0.989) and easy to measure, turbidity was used as ...