| 1. |
- Turesson, Håkan, et al.
(författare)
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Foraging behaviour and capture success in perch, pikeperch and pike and the effects of prey density
- 2004
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 65:2, s. 363-375
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Tidskriftsartikel (refereegranskat)abstract
- The effect of school size on capture success in three different piscivores, perch Perca fluviatilis, pikeperch Stizostedion lucioperca and pike Esox lucius, was investigated. Roach Rutilus rutilus were used as prey in a pool experiment where individual predators were presented prey at densities of one, two, four, eight and 16 prey, respectively. Treatments were replicated seven times for each predator species. Perch was at first virtually unable to capture a prey from a school and suffered a significant confusion effect with increasing prey density. The effect, however, was limited in the long run, as the perch was a very effective predator in its hunting strategy where it singled out and repeatedly attacked single prey irrespective of prey density or school size. Pikeperch and pike were able to attack and capture prey at any prey density equally successfully and thus did not suffer from a confusion effect. Neither did these predators receive any apparent advantages from increasing prey density. (C) 2004 The Fisheries Society of the British Isles.
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| 2. |
- Martin-Smith, K. M., et al.
(författare)
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Growth hormone increases growth and dominance of wild juvenile Atlantic salmon without affecting space use
- 2004
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 65, s. 156-172
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Tidskriftsartikel (refereegranskat)abstract
- Growth hormone (GH) was applied to Atlantic salmon Salmo salar parr (the pre-migratory freshwater life stage) to manipulate growth potential experimentally and to elucidate the effects on dominance status, actual growth, exploratory activity and home range. Experiments were conducted using seven groups of eight parr from May to September of two successive years. The fish were tagged with passive integrated transponders (PIT tags), tested for dominance, and then held in an enclosed section of a natural stream which was fitted with an array of PIT tag detectors to record space use at a definition of c. 2 m. Relationships between dominance rank, space use and growth were established over 2 weeks. The four lowest ranking fish in each group were then given a slow-release GH implant while the other fish received a placebo. The GH stimulated increase in fork length (L-F) and mass and decrease in condition factor due to the relatively greater increase in L-F. There was, however, an interaction between GH-stimulated increase in growth and season, with the hormone having an effect only during the early part of the summer. Regardless of treatment, fish that moved most around their home range grew fastest. Increased growth in GH-treated fish was associated with an increase in growth per unit movement, not increased total movement. This suggested that GH-treated fish increased their rate of short-distance (<2 m) foraging movements. Overall, space use, measured in terms of home range size and time allocation throughout the range, did not vary consistently in response to application of GH. There was a strong correlation between the weighted centre of the home range (a measure of position within the enclosure) before and after treatment, irrespective of whether fish were given GH or a placebo. The study shows that when density is low relative to carrying capacity, GH stimulates increased dominance and growth in a near-natural environment without having measurable effects on space use at a definition of e. 2 m. The results are interpreted as suggesting that high dominance status gives no significant growth advantage in a highly competitive situation, but increases foraging rate when food is abundant. Increased foraging appears to result from local changes in time budgeting rather than variations in the extent of home range and larger-scale movements within it. Thus, in areas with declining wild Atlantic salmon populations where the habitat is unsaturated and food is abundant, introduced domestic Atlantic salmon may be competitively superior. (C) 2004 Crown copyright.
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| 3. |
- Sundström, L. Fredrik, 1972, et al.
(författare)
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Density-dependent growth in hatchery-reared brown trout released into a natural stream
- 2004
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 65:5, s. 1385-1391
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Tidskriftsartikel (refereegranskat)abstract
- Hatchery-reared brown trout Salmo trutta stocked in a natural stream in addition to resident wild brown trout grew more slowly than those stocked with an experimentally reduced density of brown wild trout. In both cases, hatchery-reared brown trout grew more slowly than resident wild fish in control sections. Mortality and movements did not differ among the three categories of fish. The results showed that growth of stocked hatchery-reared brown trout parr was density-dependent, most likely as a consequence of increased competition. Thus, supplementary release of hatchery-reared fish did not necessarily increase biomass. (C) 2004 The Fisheries Society of the British Isles.
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| 4. |
- Svensson, Ola, 1971-, et al.
(författare)
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Costly courtship or dishonest display? Intensely displaying sand goby males have lower lipid content
- 2004
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 64:5, s. 1425-1429
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Tidskriftsartikel (refereegranskat)abstract
- Intensely displaying sand goby Pomatoschistus minutus males had lower lipid content, indicating that signalling increased energy expenditure, or that low condition males increased their signalling effort. Display intensity correlated positively with nest-defence and tended to correlate positively with filial cannibalism. (C) 2004 The Fisheries society of the British Isles.
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| 5. |
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| 6. |
- Amcoff, P., et al.
(författare)
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Alterations of dopaminergic and serotonergic activity in the brain of sea-run Baltic salmon suffering a thiamine deficiency-related disorder
- 2002
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Ingår i: Journal of Fish Biology. - : Elsevier. - 0022-1112 .- 1095-8649. ; 60:6, s. 1407-1416
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Tidskriftsartikel (refereegranskat)abstract
- Baltic salmon Salmo salar females displaying wiggling behaviour had significantly lower (P<0.05) hepatic and ovarian thiamine (vitamin B1) concentrations than the normal females, confirming that they suffered from a thiamine deficiency. A significantly (P<0.05) increased monoaminergic activity was found in the telencephalon and the hypothalamus of the wiggling individuals as indicated by [5-hydroxyindoleacetic acid (5-HIAA)]: [5-hydroxytryptamine (5-HT)] and [3,4-dihydroxyphenylacetic acid (DOPAC)]: [dopamine (DA)] ratios. The 5-HIAA concentrations of wiggling individuals were significantly (P<0.05) higher in the telencephalon and the hypothalamus compared to normal fish. Wiggling fish showed significantly (P<0.05) higher concentrations of the DA metabolite DOPAC in the hypothalamus and the brain stem compared to normal fish. Furthermore, the brain stem in wiggling fish contained significantly (P<0.05) less 5-HT than in normal individuals, which was also reflected in a significant (P<0.05) increase in the (5-HIAA): (5-HT) ratio. These results demonstrate an increased serotonergic and dopaminergic activity in wiggling compared to normal fish. The altered monoaminergic activity may be directly related to altered brain thiamine metabolism, but a general stress caused by thiamine deficiency and an inability to regulate swim bladder inflation may contribute. Furthermore, a changed brain monoaminergic activity may contribute to the behaviour characterizing wiggling fish.
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