Sara Calabrese has spent four years researching the best CCS environments. Foto: Eivind Senneset, UiB

Best closed conditions for salmon growth

A new doctoral study shows how salmon thrive best in terms of salinity, density and water consumption in closed facilities in sea and on land.

Published Last updated

Sara Calabrese has spent the last four years working towards an industry PhD, studying how environmental conditions affect the fish, and is now is ready to share the results. Calabrese spent three-quarters of her time on research and the rest working for Marine Harvest.

Sara Calabrese has also investigated the conditions in Marine Harvest closed facilities on Molnes. Photo: Marine Harvest

The optimal strategy for raising post-smolts in onshore recirculation aquaculture systems (RAS) in terms of salinity, current speed and time of seawater transfer is not known, so Calabrese carried out long-term studies.

"In a long-term study in fish size from 70 to 800 grams we held post-smolts in three different RAS at different salinities (12, 22 and 32 per cent) and exposed them to moderate (~ 1 body length s-1) or low (~ 0.3 body length s-1) flow rate," said Calabrese.

Her results shows that a salinity around the fish's own salinity (12 per cent) and moderate exercise has a positive effect on growth, feed utilisation, welfare and survival of post-smolts.

"At 250 and 800 grams fish from all treatments handled transition to seawater. The use of water with a salinity about 12 per cent may therefore represent a good production strategy for large post-smolts in RAS, provided that the fish can handle the transfer to open cages in the sea," concludes Calabrese, adding that further research in this area is necessary.

Optimal density

"In a commercial context, the breeding of post-smolt salmon in closed systems in the sea relies on high density of fish," says Calabrese.

In an attempt to reveal the optimum limit, five densities (25, 50, 75, 100 and 125 kg per cubic metre) were studied in flowing seawater at nine degrees for a period of eight weeks.

"Increasing density had a negative effect on growth and feed efficiency, and an increase in density from 100kg per cubic metre to 125 kg pcm caused a 42 per cent decrease in growth rate," adds Calabrese.

After eight weeks, the primary (elevated plasma cortisol) and secondary (water-ion and acid-base balance)  stress indicators were highest at the highest density. At the same time the occurrence of damage to fins and cataracts was higher at the high densities.

"Put together the results show that fish density can be increased to 75 kg per cubic metre without sacrificing performance and welfare of post-smolt salmon in CCS in the sea. Since the highest expression of important genes for cognitive ability and memory were observed at densities around 75 kg, such densities actually appear to be optimal for the welfare of the fish," said Calabrese.