Grow out - Salmons

Grow-out

As indicated earlier, the most common method of culturing salmon to market size is in floating sea cages or pens. Before transfer of the smolts to cages or pens, it is the general practice to acclimatize them gradually through intermediate salinities, over several months. Such acclimatization helps to reduce mortalities during transfer to sea farms, and prevents the sudden shock of transfer to sea water that otherwise affects feeding for weeks, and therefore their growth during the first year at sea. Smolts are transported in boats or by trucks to the site of grow-out farms, as convenient. Smolts transported by sea are generally acclimatized before transport in sea water. When transport is by truck through inland areas, smolts are carried in fresh water and the acclimatization carried out at the grow-out site. Where feasible and economical, transport by air is carried out in special tanks or plastic bags filled with water and oxygen.

Stocking of cages and enclosures is under-taken in spring and harvests taken after two or three years, depending on market requirements. The stocking density of fish in each cage may vary between 10 and 35kg fish per m³ cage at harvest. As in the case of rainbow trout, higher numbers are stocked initially and are thinned out later as they grow in size. Besides adequate feeding and frequent monitoring of the oxygen concentration of the water, the health of the fish is regularly checked. Harvesting from cages is easy. The net is pulled up until the fish are confined in a small volume of water, from which they are removed by dip nets. The use of low grilsing strains and improved rearing strategies have eliminated the need for grilse harvesting.