This study demonstrates that vegetable shortening and cocoa butter are two effective vehicles for intraperitoneal cortisol implants in juvenile teleosts, specifically brown trout Salmo trutta , residing in north temperate freshwater environments. Each vehicle showed a different pattern of cortisol elevation. Vegetable shortening was found to be a more suitable vehicle for long‐term cortisol elevation [elevated at 3, 6 and 9 da...

The vertical behaviour of 44 veteran sea trout Salmo trutta (275–580 mm) in different marine fjord habitats (estuary, pelagic, near shore with and without steep cliffs) was documented during May–February by acoustic telemetry. The swimming depth of S. trutta was influenced by habitat, time of day (day v . night), season, seawater temperature and the body length at the time of tagging. Mean swimming depth during May–September w...

A radio frequency identification ( RFID ) antenna system, build into a sledge that can be towed behind a vessel like a trawl and thereby has the potential to detect the position of a passive inductor technology ( PIT )‐tagged fish in a wide variety of habitats, is presented. By scanning for hatchery‐reared PIT ‐tagged turbot Psetta maxima released into a natural habitat, the performance of the system was compared to a standard...

The effects of disturbances from recreational activities on the swimming speed and habitat use of roach Rutilus rutilus , perch Perca fluviatilis and pike Esox lucius were explored. Disturbances were applied for 4 h as (1) boating in short intervals with a small outboard internal combustion engine or (2) boating in short intervals combined with angling with artificial lures between engine runs. The response of the fish species...

Using rainbow trout Oncorhynchus mykiss , the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre‐exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu‐contaminated water (ranging from 0 to 454 µg Cu l −1 ) and uncontaminated water in a choice ta...

Human disturbances such as angling and manual handling may have long‐term effects on the behaviour of pike, E sox lucius L ., an ecologically important species. Using continuous high‐resolution positional telemetry, this study compared the swimming activity of handled and unhandled pike in a small lake. Pike pre‐equipped with acoustic transmitters were angled and exposed to a handling protocol including measurements of length...

Anguillid eels Anguilla spp. evolved between 20 and 40 million years ago and possess a number of remarkable migratory traits that have fascinated scientists for millennia. Despite centuries of effort, the spawning areas and migrations are known only for a few species. Even for these species, information on migratory behaviour is remarkably sketchy. The latest knowledge on the requirements for successful migration and field dat...

This study tested the effect of reproduction on the volitional travel speed of mature female brown trout Salmo trutta L. The downstream travel speed in the pre‐spawning state was 0·25 m s −1 (95% CI : 0·19, 0·34) while it increased significantly to 0·65 m s −1 (95% CI: 0·49, 0·87) in the post‐spawning state. The results suggest state‐dependent travel speed in S. trutta .

The seaward migration of European silver eel Anguilla anguilla (L.) was studied during the late freshwater and early marine phase in River Gudenaa and Randers Fjord, Denmark, in the spring 2004. Migration was monitored in sections with different physical characteristics over a total distance of 46 km using automatic listening stations. Generally, eels quickly left the River Gudenaa (67% within 2 days) and stayed for up to 4.3...

The movement and mortality of stocked brown trout Salmo trutta were investigated using radio telemetry. Four brown trout left the study area whereas the remaining fish were stationary. After 5 weeks, 13 out of 50 tagged brown trout were still alive in the stream. Surviving fish had a significantly lower mean movement per day than fish, which later either died or disappeared. This difference in behaviour was most pronounced 2 t...

Radio telemetry was employed to study movements of adult female anadromous brown trout Salmo trutta (sea trout) during upstream spawning migration and following spawning in a stream with tributaries. Sea trout were monitored by manual tracking and by automatic listening stations. The latter suggested that initiation of upstream migration was positively correlated with stream discharge. Individual sea trout performed repeated u...

In February to March, wild brown trout Salmo trutta were captured by electrofishing in a natural watercourse (tributaries of the River Lille Aa, Denmark), individually tagged (Passive Integrated Transponders), and released. Representatives of the tagged brown trout were recaptured on the release sites in April by electrofishing and eventually caught in downstream smolt traps (‘migrants’) placed in the main river or by electrof...

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.

The migratory behaviour of sea‐ranched Atlantic salmon, Salmo salar L., was analysed by radio‐telemetry in the River Gudenaa, Denmark. The main objectives were to: (1) estimate mortality of returning adults through the fjord; (2) observe rate of progression and migratory pattern in the fjord and river; and (3) record whether spawning occurs in the river. Forty‐two returning salmon (19 males and 23 females of total body length...

Radio‐tagged and dye‐marked adult pike Esox lucius L. were recaptured in a reservoir 1 year after tagging. There was no significant difference in length or weight growth rate between the two groups of fish and no change in their condition factor.

Smolt migration through a shallow and turbid hydro‐reservoir in a major Danish river system was investigated using radiotelemetry. Hatchery‐reared 1+‐year‐old Atlantic salmon, Salmo salar L., smolts of equal size from two different non‐native strains were radio‐tagged and followed during their downstream migration through the 12‐km‐long reservoir. A total of 50 salmon smolts, 25 of Swedish (Øtran River) and 25 of Irish (Burris...