Sibling recognition in juvenile Arctic charr, Salvelinus alpinus (L.)

Juvenile Arctic charr, Salvelinus alpinus (L.), from two full sibling groups were studied concerning the possible existence of chemical cues with information about kinship. Each full sibling group was divided into two groups with the same number of specimens and placed in two separate aquaria. The division coincided with the start of exogenous feeding. Preference tests were performed about 7 and 10–13 months after the division. Due to the increasing size of experimental fish, two different sizes of apparatus were used. The first series of experiments was performed in a small Y-maze fluviarium and the second series in the large standard fluviarium. The momentary positions of one fish at a time in the test area were recorded by time-lapse photography with a 16-mm film camera and filtered flashlight (no transmittance <670 nm). The fish were given a choice between two water qualities; thus the following comparisons were made: (i) unconditioned water ν. water scented by siblings from the same aquarium; (ii) unconditioned water ν. unfamiliar non-siblings; (iii) siblings from the same aquarium ν. unfamiliar non-siblings; (iv) siblings from a separate aquarium ν. unfamiliar non-siblings; (v) siblings from the same aquarium ν. siblings from a separate aquarium. The test fishes preferred water scented by siblings over non-siblings, even though the siblings were taken from a separate aquarium. Nevertheless, they were attracted to water scented by unfamiliar non-siblings in preference to unconditioned water. No preference was shown between chemical cues from siblings taken from the same and a separate aquarium.