The findings, published in a report, show large differences between farms and between parts of the country.
The report also points out opportunities for great success for systems with high losses.
The project was funded by FHF (Fishery and Aquaculture Industry Research Fund) and covered salmon and rainbow trout released in autumn 2010 and spring and autumn 2011.
The results showed a loss of 16.3 per cent for salmon and 18.3 per cent for rainbow trout.
There were marked differences in the causes of losses among fish groups, localities and different geographic locations.
