There are a number of possibilities John.
1. The fish may simply be frightened hence the timid behaviour.
2. The fish may have suffering from parrasites hence the flashing (swims on it's side in an attempt to scrape off whatever is bothersome)
3. The hiding may be due to the Koi feeling unwell, due to bacterial or parrasitic infection.
Try and befreind a local Koi keeper and see if you can get them to take a look for you. A microscopic examination may be required to identify parrasites but you need somebody knowledgable to look at the fish and advise you accordingly.
Posted on Apr 17, 2005, 9:44 PM from IP address 213.120.101.21