Spreading diseases

摘要

Perch in Lake Windermere in the UK used to live to a ripe old age. While the average age of fish caught and released by researchers was around 5 years, a few individuals were as old as 20. Then in 1976, an unidentified disease wiped out 99 per cent of adult fish and continued to preferentially kill older fish for years afterwards. Since then, no fish older than 7 have been caught. According to Jan Ohlberger of the University of Oslo, Norway, the perch (Percofluviotilis) evolved very quickly in response. They now become sexually mature at an earlier age, which increases their chances of breeding before they get killed by the disease (Proceedings of the Royol Society B, vo1278, p 35). While the disease is thought to have spread naturally in the lake, Ohlberger points out that many devastating disease outbreaks in plants and animals are a result of human activity.