Early familiarity has fitness consequences for Arctic char (Salvelinus alpinus) juveniles

Familiarity is an important factor reducing aggressiveness among individual s. Because of the reduced energy and time expenditure due to lowered aggres sion, individuals would be expected to perform better in groups of familiar conspecifics as compared with individuals in groups of strangers. However, few studies have examined potential fitness consequences of familiarity. W e created familiar (from tanks where several thousands of unrelated fish ha d been kept since fertilization) and unfamiliar (by combining fish from sev eral tanks) groups of underyearling Arctic char (Salvelinus alpinus) and fo llowed their performance for a 21-day period. Familiarity within groups enh anced survival and body condition of the fish. The fish in familiar groups also grew better in weight and in length. Furthermore, familiar fish differ ed less in length variation after the experimental period compared with fis h reared in unfamiliar groups. There was also a tendency towards similar di fference in the variation of weight. These results provide direct evidence for beneficial fitness consequences of early familiarity in Arctic char.