Long-term retention of surgically implanted radio transmitters in pikeperch

Radio-tagged pikeperch Stizostedion lucioperca (55–74 cm L _T) were recaptured in a reservoir by anglers 52–55 months after tagging. A total of four fish were recaptured during the summer of 2001. These recaptures are remarkable because of the long period between tagging and recapture and because only one (of 15 potential) tagged pikeperch had been caught in the long period since tagging.     

Reservoir to river passage of age‐0+ year fishes,indication of a dispersion pathway for a non‐native species

This study demonstrates passage of age‐0+ year individuals of pikeperch Sander lucioperca, common bream Abramis brama and non‐native tubenose goby Proterorhinus semilunaris from the Nové Mlýny Reservoir into the River Dyje (Danube River basin, Czech Republic) through the turbine of a hydropower facility. Most fishes had standard length (L_S) in the range 12–33 mm. Seasonal patterns corresponded with spawning activity, i.e. an early single spawning event for S. lucioperca, multiple spawning events for A. brama and continuous spawning with a later start and prolonged duration for P. semilunaris. Sander lucioperca, P. semilunaris and larger A. brama (>22 mm) drifted almost exclusively during the dark; smaller A. brama displayed no preference for light or dark. Proterorhinus semilunaris displayed significantly lower mortality than other species when passing through the turbine (3% compared to 18%). The passage of high numbers of P. semilunaris from the reservoir (estimated at 473 000 individuals per year), and their subsequent mass downstream drift, may have contributed to rapid population establishment along the River Dyje and the quick downstream expansion.     

Microvideography of gas bladder inflation in larval walleye

High-resolution microvideograph observations supported the hypothesis that first filling of the gas bladder of larval walleye Stizostedion vitreum is accomplished by the fish penetrating the air-water interface to gulp air, then transmitting a swallowed air bubble through the gut and the pneumatic duct to the gas bladder. The snout of the larva penetrated the water surface with extension of most of the mouth into the air for only 1.5 s. An air bubble ( c. 100 μm) in the foregut was broken up into progressively smaller bubbles (10–15 μm), presumably by the combined effect of surfactant derived from the gall bladder and mechanical (peristaltic) action of the gut. These smaller bubbles seemed to be aligned in the pneumatic duct before being forced to the gas bladder by pressures generated from peristalsis.     

Population genetic structure, phylogeography and spawning philopatry in walleye (Stizostedion vitreum) from mitochondrial DNA control region sequences

Mitochondrial (mt) DNA control region sequences were used to test the genetic and phylogeographic structure of walleye Stizostedion vitreum populations at different geographical scales: among spawning sites, lake basins, lakes, and putative glacial refugia in the Great Lakes region. Sequencing 199 walleye revealed nucleotide substitutions and tandemly repeated sequences that varied in copy number, as well as in sequence composition, in 1200 bp of the mtDNA control region. Variable numbers of copies of an 11-bp tandem repeat showed no geographical patterning and were not used in further analyses. Substitutions in the other areas of the control region yielded 19 haplotypes, revealing phylogeographic structure and significant differences among glacial refugia, lakes, basins and some spawning sites. Differences among spawning populations were consistent with reduced gene flow, philopatry and possible natal homing. Analysis of spawning populations showed consistency of genotypic frequencies among years and between males and females, supporting philopatry in both sexes. The unglaciated plateau in southern Ohio, USA housed a very different haplotype that diverged prior to the Missouri, Mississippi and Atlantic glacial refugia types. Haplotypes from the three refugia colonized the Great Lakes after retreat of the Wisconsin glaciers, and their present distribution reflects the geography of their prior isolation and differential colonization. Populations that became associated with spawning localities appear to have diverged further due to philopatry, resulting in fine-scale phylogeographic structuring.     

Migratory behaviour of adult pikeperch (Stizostedion lucioperca) in a lowland river

The behaviour of radio-tagged adult pikeperch (Stizostedion lucioperca (L.)) from two areas in the Danish River Gudenaa were recorded prior to, and during the spawning period. Eight of 13 tagged fish in the lower reaches of the river were located throughout the whole study. Five of these fish moved upstream to various sites in the river prior to spawning, which occurred from late April to June. The three remaining fish moved to the fjord. These movements were interpreted as a spawning migration, and it is suggested that the lower reaches of the River Gudenaa constitute an over-wintering area for pikeperch, which use different spawning areas. Ten pikeperch caught just downstream of an impassable hydropower plant were radio-tagged and translocated upstream of the dam to a reservoir. Within a week, half of the fish moved to a lake situated more than 30 km upstream the reservoir. This behaviour is hypothesised to be a homing response. The study reveals that the pikeperch is a highly mobile species with a complicated migration pattern, even in relatively small river systems.     

Use of Biochronology to Examine Interactions of Freshwater Drum, Walleye and Yellow Perch in the Red Lakes of Minnesota

Growth histories for freshwater drum, Aplodinotus grunniens, walleye, Stizostedion vitreum, and yellow perch, Perca flavescens, were constructed using calcified structures for the period 1947 through 1996 for the Red Lakes, Minnesota. Increased walleye growth and decreased yellow perch growth were observed over the period from 1983 to 1996, which are attributed to intensive fishing resulting in decreased intraspecific competition in walleye and increased intraspecific competition in yellow perch through release from predation. Strong year-classes of yellow perch were positively correlated with walleye growth (r=0.57, p-value=0.042). There was no evidence for interactions of walleye or yellow perch with freshwater drum. Freshwater drum growth (r=0.680, p-value=0.0001) was more highly correlated with temperature than were walleye (r=0.386, p-value=0.006) and yellow perch growth (r=0.303, p-value=0.036).     

Impact of flood on distribution of bathypelagic perch fry layer along the longitudinal profile of large canyon-shaped reservoir

Previous studies have shown that under normal spring conditions, the layer of bathypelagic perch Perca fluviatilis fry (BPF) is equally distributed along most of the longitudinal profile of reservoirs. In the first half of June 2004, local flooding entering the large canyon‐shaped Orlík Reservoir (Czech Republic) completely flushed out the existing fry community from the 31 km long riverine part of the reservoir. The pelagic zone in this reach was then recolonized by cyprinid (mainly roach Rutilus rutilus and bream Abramis brama) fry being of either littoral or riverine origin. Subsequently, the BPF layer was recorded only in the 22 km long lacustrine part of the reservoir. In the upper reach of this part where, due to the sudden increase in volume, the water current slowed down rapidly and fry originating from both riverine and central parts of the reservoir gathered in high numbers, two distinct BPF layers were observed. During mid‐day, the upper BPF layer, created predominantly by shoaling fishes (abundance >126 000 individuals ha^?1), occurred between 6 and 10 m. A second, lower BPF layer, created by non‐shoaling fishes exclusively (30 000 individuals ha^?1), was recorded between 12 and 17 m depth. Both upper and lower BPF layer were composed of perch (69·6 and 66·8% in abundance respectively) and zander Sander lucioperca (29·8 and 28·6% in abundance respectively). In the lower BPF layer, ruffe Gymnocephalus cernuus also contributed considerably to the fry assemblage (4·0% in abundance). Perch from the upper BPF layer (mean 25·1 mm total length, L_T) did not differ in size from perch from the lower BPF layer (mean 25·0 mm L_T). Similarly, zander from the upper BPF layer (mean 27·2 mm L_T) were almost the same size as those from the lower BPF layer (mean 26·9 mm L_T). Perch from both BPF layers, however, were noticeably smaller than zander. The results from acoustic survey and complementary net catches suggest that no epipelagic perch fry were found in the reservoir where thermal stratification had been destroyed by flooding and windy weather.     

Annual movement and migration of adult pikeperch in a lowland river

The downstream migration of 46–66 cm radio-tagged adult pikeperch Stizostedion lucioperca , in the River Gudenaa, Denmark, from late September to late December, coincided with a reduction in the frequent occurrence of prey fish in the tagging area, and hence was interpreted as a feeding migration. The upstream migration from March to mid-April in spring took place prior to spawning which occurred from late April to June.     

Neurons controlling the gill vasculature in five species of teleosts

Summary A plexus of nerve fibers encompassing neuronal perikarya is present within the gill filament; it surrounds the proximal portion of the efferent filament artery and the efferent lamellar arterioles. This innervation resembles the pattern described for the area around the sphincter of the efferent filament artery: acetylcholinesterase-positive neurons and fibers, fast-fading yellow-fluorescent neurons and fibers, long-lasting green-fluorescent fibers. In addition, synaptic contacts between the different components suggest functional interrelationships. Nerves evidently control the efferent limb of the filament circulation including the sphincter of the efferent filament arteries, the proximal portion of the efferent filament arteries proper, and their corresponding efferent lamellar arterioles. However, the distal portion of this system is poorly innervated.