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A morphometric method for estimation of total lipid level in live Arctic charr: a case study of its application on wild fish

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Linear body measurements were made on wild Arctic charr Salvelinus alpinus parr (100–200 mm LF) from two populations in northern Norway during spring (May), summer (June and July) and autumn (October). To reduce handling stress, a method was developed were dorsal and ventral body measurements could subsequently be taken easily from a single picture of the anaesthetized fish. Multiple regression analyses investigated the possible correlation between the body measurements and both total and percentage lipid content of the fish. For both populations and during all seasons, the regression equations gave better estimates for total lipid than for percentage lipid. The regression equations for total lipid accounted for between 67·7 and 89·5% of the variance in lipid content for the different seasons within the lakes. The pooled data within each lake accounted for 62·9 and 81·0% of the variance in total lipid, while the pooled data for both lakes accounted for 67·7% of the variance. In general, the condition factor alone did not give a satisfactory estimate of lipid content of the Arctic charr (r2 = 0·003–0·521). Shrinkage on validation values was high (0·20–0·52). Employing a ridge regression method resulted in models with lower r2 values and lower shrinkage values (indicating more stable models). Published equations used for hatchery-reared Arctic charr could not be used on wild fish from the same population. The close correlations between actual and predicted lipid levels found in this study show that morphometric measurements can predict total lipid levels in wild Arctic charr with reasonable accuracy. The most accurate results were obtained when equations were derived from each data set. Therefore, the method has the potential within a single study to estimate lipid levels in live fish as long as some fish can be sacrificed to develop a unique regression equation for each population or experiment.

Keywords: Salvelinus alpinus; collinearity; fat; life history; ridge regression

Document Type: Regular Paper


Affiliations: 1: Norwegian Institute for Nature Research, Polar Environmental Centre, N-9296 Tromsø, Norway and 2: The Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway

Publication date: 2003-03-01

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