Search results for "BROWN TROUT"
showing 10 items of 63 documents
Epizootiology of protozoans in farmed salmonids at northern latitudes
1997
Abstract Protozoan ectoparasites were examined in a northern salmonid fish farm over a 10-year period, June 1984–May 1994, by the same researcher, with similar catching and sampling procedures throughout. Husbandry procedures remained constant during the study, e.g., fingerlings were kept in steel tanks and yearlings in both steel tanks and earth ponds. Ichthyobodo necator, Chilodonella hexasticha and Ichthyophthirius multifilurs infections were treated with formalin, salt and malachite green-formalin baths, respectively, whenever any parasites were found. Altogether 10 790 randomly sampled salmon (Salmo solar), sea trout (S. trutta m. trutta) and brown trout (S. trutta m. lacustris) were s…
Nocturnal drift of mayfly nymphs as a post-contact antipredator mechanism
2000
SUMMARY 1. The predominantly nocturnal constrained drift of stream invertebrates is commonly regarded as a behaviour that avoids encounters with visually foraging fish in the water column. The alternative explanation, that drift peaks are caused by bottom-feeding, nocturnal predators, has rarely been tested. 2. We examined these hypotheses by collecting invertebrate drift in five streams in northern Finland: one with brown trout (Salmo trutta, a drift-feeding fish), one with alpine bullhead (Cottus poecilopus, a benthic fish), one with both species, and two fishless streams. 3. Drift by Baetis mayflies was aperiodic or slightly diurnal in both fishless streams on all sampling occasions. In …
Finnish salmon resistant to Gyrodactylus salaris: a long-term study at fish farms.
1996
Abstract The occurrence of Gyrodactylus salaris on Baltic salmon ( Salmo salar ), sea trout ( S. trutta m. trutta ) and brown trout ( S. trutta m. lacustris ) was examined from 1984 to 1993 at 4 fish farms (A, B, C and D) that produce smolts for stocking in northern Finland. No G. salaris was found on the sea or brown trout, but it did occur on salmon for 6–7 years at farms B, C and D, the prevalences of infection being 9.5%, 17.7% and 8.8% for salmon yearlings and smolts during that time, respectively, but less than 1.2% for fingerlings at farms B and C. Only brood stock salmon were infected at farm A in 4 years. The abundances of G. salaris increased during the second winter of each year …
Effect of glochidia infection on growth of fish : freshwater pearl mussel Margaritifera margaritifera and brown trout Salmo trutta
2019
AbstractEffect of freshwater mussels’ (Unionoida) glochidia on the growth of fish host has remained poorly studied. We compared the specific growth rate of the juvenile, PIT-marked brown trout (Salmo trutta) between uninfected controls to those experimentally infected (average initial intensity of infection 8000 fish−1) with Margaritifera margaritifera glochidia, kept in high and low feeding. Growth and mortality of fish were monitored for 10 months. Our hypothesis was that glochidiosis would impair the growth of fish. According to our hypothesis, infected fish gained statistically significantly less weight than the control fish throughout the experiment. A proportional increase in weight o…
Infection of brown trout with Diphyllobothrium dendriticum procercoids.
1997
The aims of this experimental study were to develop a practical method of controlling the number of Diphyllobothrium dendriticum procercoids delivered to a fish host; to examine the effect of different procercoid doses (3, 7 and 15) on the plerocercoid level in fish; and to examine the potential mortality caused by plerocercoids. The experiment was terminated after 2 months. The prevalence of infection at the lowest dose level, 17.2%, was statistically significantly lower than at medium and high levels, 63.3% and 56.7%, respectively. The mean intensity increased slightly along with the dosage. The contribution of D. dendriticum to the death of a few fish could not be proved. It is concluded…
Tuning host specificity during the ontogeny of a fish ectoparasite: behavioural responses to host-induced cues
2003
The choice between two alternative hosts, brown trout (Salmo trutta) and roach (Rutilus rutilus), and the response to visual and olfactory cues were studied in the ontogeny of Argulus coregoni. The initial preference of the smallest parasites for brighter roach changed at the age of 2 weeks, at the size of about 2 mm, for trout, a typical salmonid host. Younger argulids were attracted by a non-specific visual stimulus (white disc over dark background), and they did not respond to olfactory stimulation (fish-conditioned water). Later, the response to visual stimuli was modulated by trout-conditioned water, but not by that conditioned by roach. The primary role of vision, particularly in earl…
Cardiovascular, ventilatory and haematological responses of brown trout (Salmo trutta L.), to the combined effects of acidity and aluminium in humic …
1995
Two year old brown trout (Salmo trutta L.) were exposed for 7 days to pH 4.7 alone and with aluminium at concentrations of 0.28 and 0.45 mg l−1, respectively, in the water of River Rutajoki, Central Finland. The labile aluminium accounted for less than 30% of the total added amount in the humic water. During the exposures the fish were monitored by a non-contact bioelectronic monitoring system which records heart and ventilation rates of the fish. Terminal blood samples were obtained to evaluate the degree of stress. No mortality occurred during any of the exposures. Acid stress alone and with aluminium caused an immediate acute response in heart and ventilation rates, which remained higher…
Bioelectronic monitoring of parasite-induced stress in brown trout and roach
1996
A non-contact bioelectronic monitoring system was used to record changes in heart rate, ventilation rate and swimming activity in brown trout Salmo trutta and roach Rutilus rutilus, following exposure to two species of cercariae of digenean trematodes: Diplostomum pseudospathaceum which is a common parasite in the lens of fishes and xiphidiocercariae of Plagiorchis elegans, a parasite of anatid birds, both of which have the snail Lymnaea stagnalis as their first intermediate host. Swimming activity increased significantly in roach exposed to Diplostomum cercariae at densities as low as 3.8l−1 and remained elevated for 24–36 h post exposure. Brown trout showed no response when exposed to low…
Intercohort competition causes spatial segregation in brown trout in artificial streams
1999
When together in a flume, 13-cm LS (age-1) trout appeared to increase their activity and behaved more aggressively, whereas 10-cm LS (age-0) trout tended to move less and were rarely aggressive in the presence of the larger size class. Both size classes were less mobile and preferred lower water velocities in winter than in summer, and increased their use of instream cover in winter. When both size classes were present, only small trout decreased their use of low water velocities and cover. The results indicate that intercohort competition may cause spatial segregation among size groups of brown trout, especially in winter when trout attempt to minimize their maintenance costs.
Taimenen mädin säilyvyys ja alkioiden kasvu Savijoen kipsinlevitysalueella
2019
Pelloille tehtävän kipsinlevityksen vesistövaikutuksia tutkittiin Helsingin yliopiston ja Suomen ympäristökeskuksen yhteishankkeessa ”SAVE - Saaristomeren vedenlaadun parantaminen peltojen kipsikäsittelyllä”. Hanke oli ympäristöministeriön rahoittama hallituksen kärkihanke. Siinä missä kipsin, eli kalsiumsulfaatin, levitys on vähentänyt pelloilta tulevaa fosforikuormitusta, se on toisaalta nostanut pilottialuetta halkovan Savijoen sulfaattipitoisuuden kolminkertaiseksi. Suuren sulfaattipitoisuuden tiedetään olevan haitallista vesieliöille, kuten kaloille. Näin ollen Jyväskylän yliopisto selvitti kipsinlevityksen vaikutuksia taimenen (Salmo trutta) varhaisten elinvaiheiden säilyvyyteen ja ka…