1. Introduction
The primary aim of applied breeding programmes in aquaculture is to improve the productivity and thus the profitability. For salmonid species, a family based breeding program typically consists of three tiers; i) a breeding nucleus that produces candidates for the next generation of nucleus families and for the multipliers, ii) the multiplier tier that produces fingerlings for the grow-out tiers and iii) the grow-out tier that produces slaughter fish (Gjedrem, 1985). In most cases, the material provided by the multipliers merely reflects the average genetic level of the material the multiplier receives from the nucleus, as no selection pressure is applied at this stage, but Toro (1998) suggested development of specialised parent lines and Gjerde and Gjedrem (Gjedrem, 2005 and Gjerde, 2005) raised a more detailed idea of producing more customised genetic material suited for specific farm environments and market segments.