Search results for "Rainbow"

Impaired crypsis of fish infected with a trophically transmitted parasite

2005

Trophically transmitted parasites may enhance their transmission by altering the phenotype of infected hosts to increase their vulnerability to predation by the next hosts in the life cycle. In an experimental study, we investigated whether the parasite Diplostomum spathaceum (Trematoda) alters cryptic coloration and cryptic behaviour of infected rainbow trout, Oncorhynchus mykiss, so that they would be more conspicuous to avian predators. The parasite reduces the vision of fish by lodging in the eyes and inducing cataract formation, which gives it an opportunity to affect fish crypsis. We examined the effect of the parasite on the ability of fish to adjust their coloration to the environme…

Complementary approaches for assessing protein sources in fish feed

2018

Fluctuating fishmeal (FM) prices and declining marine fish stocks have led to the current trend of replacing dietary FM with plant proteins (PP) in fish feed. PPs offer challenges both with respect to nutritional quality and the occurrence of antinutrients. The assessment of utilisation efficiency of PPs for growth is important for the sustainable production of fish feed. The overall aim of this thesis was to investigate the applicability of stable isotope analysis in combination with respirometry in the evaluation of dietary PPs for juvenile rainbow trout (Oncorhynchus mykiss). The dietary PPs were corn gluten meal (CGM), rapeseed protein concentrate (RPC) and potato protein (PoP). Complet…

Effects of temperature and feeding regime on compensatory growth of rainbow trout, Oncorhynchus mykiss

2006

Indirect estimation of stomach volume of rainbow trout Oncorhynchus mykiss (Walbaum)

2005

The main hypothesis of this study was that if stomach volume is correlated with food intake it can be estimated without laborious and destructive direct measurement. Rainbow trout, Oncorhynchus mykiss (Walbaum), ca. 500^1300 g, were starved for 1, 4, 8 or16 days at151C after which they were fed in excess with dry pellets containing known amounts of X-raydense markers. Immediately after feeding the ¢sh were killed, X rayed and weighed. Then the stomach was dissected, its contents removed and weighed, and stomach volume was measured. X-ray plates were developed and feed intake was estimated based on the amount of marker. All measured variables correlated positively with stomach volume. The be…

Compensatory growth in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually

2004

Abstract The effect of feed cycling on compensatory growth was examined in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), held individually at 15 °C. Fish were fasted for 2, 4, 8, or 14 days and then refed until either their relative feed intake differed by less than 10% of fed controls, or the duration of the refeeding period was four times the fasting period. After 80 days, fish fasted for 8 days at a time were smaller than controls, or fish experiencing 2 or 4 days of fasting, while fish fasted for 14 days did not differ from other groups. There were no differences in visceral fat or hepatosomatic indices, but within-treatment variation was high. Fish subjected to fasting display…

Eye fluke-induced cataract formation in fish: quantitative analysis using an ophthalmological microscope

2004

We examined the parasite-induced cataract formation in rainbow trout (Oncorhynchus mykiss) using slit-lamp microscopy to determine the relationship between cataract intensity and number of Diplostomum spathaceum parasites that were established in the lens. Cataract intensity increased significantly with parasite burden, but was also affected by the pattern of exposure to the parasite cercariae. The slit-lamp methodology proved useful in scoring the cataracts since it provides a 3-dimensional view into the lens and gives an actual picture of the location and intensity of the cataracts, which allows detailed investigations of mechanisms underlying cataract formation in various fish species. P…

Androgen metabolism in the skin of the rainbow trout (Oncorhynchus mykiss)

1993

Pieces of skin of male and female rainbow trout (Oncorhynchus mykiss) were incubated with testosterone and 11-ketotestosterone as substrates. In immature fish the conversion rate was low. In non-spawning adult males 11-ketotestosterone was reduced to 5α-11KDHT (up to 5.2%). In the fish in spawning condition the 5α-reduction rate was only about 1 to 2%. In the same specimens incubated with testosterone a high 11β-hydroxylase activity (23.8-25% in the male and 13% in the female skin) was found. Similar sex specific differences were observed for the occurence of 5α-reduced metabolites (about 20% in the male and 13% in the female tissue).

Ultraviolet B radiation induced alterations in immune function of fish : in relation to habitat preference and disease resistance

2009

Runsas altistuminen auringolle on tunnetusti haitallista ihmisten ja eläinten hyvinvoinnille. Eveliina Markkula tutki väitöskirjatyössään, miten ultravioletti B (UVB) -säteilylle altistuminen vaikuttaa kalojen vastustuskykyyn ja tautialttiuteen.- Ilmakehän otsonikerroksen oheneminen viime vuosikymmenten aikana on johtanut UVB-säteilyn lisääntymiseen maan pinnalla. UVB-säteily tunkeutuu myös kirkkaisiin järvi- ja merivesiin ja voi näin aiheuttaa haittaa kaloille, Markkula kertoo.UVB-säteilyn on jo aiemmin todettu lisäävän kalojen varhaisten elinvaiheiden epämuodostumia ja kuolleisuutta. Kertaluonteinenkin altistuminen lampuilla tuotetulle UVB-säteilylle aiheuttaa muutoksia kalan immuunijärje…

Toxicity of retene and pyrene on fish at different light conditions

2011