Chemo-attraction between juveniles of two sympatric stocks of Arctic charr, Salvelinus alpinus (L.), and their gene frequency of serum esterases

Juvenile Arctic charr, Salvelinus alpinus (L.), from two spawning locations, Abranna stock and Holderstrommen stock, in Lake Torron, Sweden, were used crosswise as odour donors and receivers in fluvarium tests concerning attraction to stock-specific odours. The momentary positions of the odour-receiving charr were recorded with a film camera and filtered flash light (no transmittance < 670 nm). One test fish at a time was placed in the test area to choose in darkness between two water qualities, viz. (i) control tests were run with pure water all over the test yard; (ii) pure water and water having passed 20 specimens of their own stock; (iii) pure water and water conditioned by the presence of 20 specimens of the sympatric stock; (iv) water conditioned by passing 20 specimens of either stock. Specimens of both stocks were attracted to water scented by either stock. The abranna (AB) but not the Holderstrommen stock (HO) showed significantly stronger attraction to scent of their own stock than to the sympatric stock. This was supported in tests with simultaneous supply of AB and HO-scented water, when AB significantly preferred the water having passed specimens of its own stock, while HO did not prefer any water quality. Out of 300,65 specimens from each stock were analyzed as to the gene frequency of serum esterases. The HO sample, in contrast to AB, was heterogeneous as the frequency of heterozygotes was lower than that expected under Hardy-Weinberg equilibrium. No heterogeneity in gene frequencies was observed between AB and HO. The results of both odour attraction tests and the gene frequency analysis points to AB, in contrast to HO, as being offspring from a discrete stock.