Habitat use of three sympatric whitefish Coregonus lavaretus forms was determined using hydroacoustics, pelagic trawling and epibenthic gillnetting in the subarctic Lake Muddusja¨rvi during the day and night in June, August and September. Whitefish constituted 97% of the numerical catches and whitefish with high number of gill rakers (DR) were the most abundant whitefish form. Forms with low numbers of gill rakers used only epibenthic habitats during both the day and night in all study periods: large whitefish with low numbers of gill rakers (LSR) dwelled mainly at depths 0-10 m, whereas small whitefish with low numbers of gill rakers (SSR) used deeper (>10 m) habitats. LSR and SSR whitefish consumed mainly benthic macroinvertebrates during all study occasions. The planktivorous DR whitefish used both epibenthic and pelagic habitats, but vertical habitat selection varied both over time of day and season.

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The field data from four humic lakes suggested that water colour may have both direct and indirect effects on inter- and intra-specific interactions of perch Perca fluviatilis and roach Rutilus rutilus. The results agree with suggestions that, compared with R. rutilus, P. fluviatilis may be an inferior forager on zooplankton in highly coloured water. As an indirect effect, water colour decreases the coverage of macrophytes and limits suitable littoral habitats, benefiting R. rutilus over P. fluviatilis. Perca fluviatilis benefiting from complex habitats does not have the advantage in macrophyte-poor highly coloured water.

According to logistic regressions derived for pike Esox lucius and burbot Lota lota, the probability of ingesting fishes in Lake Muddusjärvi, northern Finland, was 50% at 19·3 and 22·1 cm LT, whereas Arctic charr Salvelinus alpinus and brown trout Salmo trutta shifted to piscivory at the lengths of 25·7 and 26·4 cm LT. The specialist piscivores, pike and burbot, consumed more prey species and took a wider range of prey sizes than Arctic charr and brown trout. The prey length for all predators increased in relationship to predator length. Whitefish Coregonus lavaretus was the dominant prey species in the lake and in the diet of all the piscivorous species. The whitefish population was divided into three forms, of which the slow‐growing, and the most numerous densely rakered whitefish form (DR), was selected by all predator species. This form also had the smallest average size and widest habitat range, utilizing both pelagic and epibenthic habitats. Two sparsely rakered whitefish forms (LSR and SSR) occupied only epibenthic habitats and had lower relative densities than DR. These forms, LSR and SSR, had a minor importance in the diet of predator species.

The long-term clinical outcome after anatomical reconstruction and tenodesis in the treatment of chronic anterolateral ankle instability was assessed in a retrospective multicentre study. The first group (AR) consisted of 25 patients (mean age at operation 22 yrs +/- 5.7) who underwent anatomical reconstruction and the second group (TE) of 29 patients (mean age 23 yrs +/- 6.6) who underwent tenodesis. For both groups, the mean follow-up period was 12.3 yrs (AR +/- 2.5 yrs, TE +/- 2.7 yrs). At physical examination, there were significantly more patients in the TE group (n=18) with a positive anterior drawer sign as compared with the AR group (n=7) (p=0.02). Medially located degenerative changes in the ankle joint as seen on standard radiographs were seen more often in the TE group (n=7) than in the AR group (n=1) (p=0.03). The mean talar tilt, 4.7 degrees in the AR group vs 6.9 degrees in the TE group, (p=0.02) and anterior talar translation, 2.9 mm in the AR group vs 4.3 mm in the TE group, (p=0.04) were significantly higher in the TE group at radiographic stress examination. According to the rating system developed by Good et al. (1975), significantly fewer patients in the TE group (n=8) had an excellent result as compared with the AR group (n=15) (p=0.03) and more patients in the TE group (n=9) had a fair or poor result (p=0.04) as compared with the AR group (n=2). We conclude that a tenodesis procedure does not restore the normal anatomy of the lateral ankle ligaments. When compared with anatomical reconstruction, a tenodesis leads to inferior results in terms of functional and mechanical stability, as well as overall satisfaction at long-term follow-up.

– The aim of this study was to explain the growth differences of the two sympatric sparsely rakered whitefish (Coregonus lavaretus (L.)) forms in the subarctic Lake Muddusjärvi by comparing their habitat and food selection to available benthic food resources. The average number of gillrakers was 22.9 for large sparsely rakered whitefish (LSR) and 16.8 for small sparsely rakered whitefish (SSR). LSR dwelled primarily in the littoral zone at depths < 10 m, whereas SSR used mostly profundal habitats in depths > 10 m. LSR and SSR consumed mainly benthic macroinvertebrates, their abundance, biomass and diversity was highest in the littoral, decreasing towards the profundal. As the individual size of fish increased, LSR was able to shift to larger food items, which were available in the littoral. Possibility of SSR to ontogenetic food shift was scarce in the profundal, where availability of larger benthic macroinvertebrates was low. Because of abundant food resources in the littoral, growth rate of LSR was faster than that of SSR.

Global warming is expected to result in considerable changes in northern European freshwater fish populations, fisheries and aquaculture. Shifts towards cyprinid and percid dominance in fish assemblages are expected, together with a decrease and collapse of salmonid and other coldwater fish populations. Most of the evident changes will occur in shallow lakes, where no thermal stratification occurs. The potential ranges of some fish species will shift northwards but pronounced changes will occur in the relative abundance of individual fish species. Total fish production will increase but because of changed composition of fish communities the commercial and recreational value of catches will decrease. Salmonid aquaculture productivity will increase provided that fish farmers adapt to new circumstances and cold, oxygenated water is available in larger quantities during summer.

Adaptive phenotypic divergence of sympatric morphs in a single species may have significant evolutionary consequences. In the present study, phenotypic impacts of predator on zooplankton prey populations were compared in two northern Finnish lakes; one with an allopatric whitefish, Coregonus lavaretus (L.), population and the other with three sympatric whitefish populations. First, we examined whether there were phenotypic associations with specific niches in allopatric and sympatric whitefish. Second, trait utility (i.e. number of gillrakers) of allopatric and sympatric whitefish in utilizing a pelagic resource was explored by comparing predator avoidance of prey, prey size in environment, and prey size in predator diet. The allopatric living large sparsely rakered (LSR) whitefish morph, was a generalist using both pelagic and benthic niches. In contrast, sympatric living whitefish morphs were specialized: LSR whitefish was a littoral benthivore, small sparsely rakered whitefish was a profundal benthivore and densely rakered (DR) whitefish was a pelagic planktivore. In the lake with allopatric whitefish, zooplankton prey did not migrate vertically to avoid predation whereas, in the lake with sympatric whitefish, all important prey taxa migrated significantly. Trait utility was observed as significantly smaller size of prey in environment and predator diet in the lake with DR whitefish than in the lake with only LSR whitefish.