The BC Province's fish test tables show 29 million fish farm fish dead from all causes since 2003. Some deaths are legitimate such as 20K of smolts dying per fish farm plant on being put in saltwater.
Mary Ellen Willing, from fish farms, says fish deaths are about 1.5%. That comes out to about 10 million since 2003. That implies that the provincial percentage is 4.35% of fish farm fish die. Whether 10 million dead fish, or 29 million dead fish, a lot of fish are killed in in-ocean fish farming in BC.
The fish death figures from Norway are far higher: 16% in central Norway in 2009 (Trøndelag and Møre og Romsdal), or 10.6 million of 65.6 million.
The figure in 2008 for this area from disease was 22%, less than for Norway as a whole. This suggests that the BC deaths will increase dramatically over time for in-ocean fish farms.
This link is in Norwegian, but you can translate it at Google: http://www.nrk.no/nyheter/distrikt/nrk_trondelag/1.7859486?mid=51.