Warmer seas leave salmon emaciated

High sea temperature severely reduces appetite and growth rates in farmed salmon
November 10, 2011

Salmon prefer cool water. When the temperature reaches 18-19 degrees, they lose their appetite. Salmon farmers in the southwest of Norway have already experienced this several times in the course of this century, and this has now been scientifically confirmed:

“Salmon that live in water at a temperature of 19 oC reduce their food intake by 50 percent compared to those that live at 14 oC, and  grow correspondingly more slowly,” said NIFES scientist Ernst Hevrøy.

His analysis has revealed that the hunger-regulating hormone ghrelin is suppressed at high temperatures, and this in turn inhibits the stimuli from the neurotransmitter in the brain that regulates appetite and food intake.

Major consequences
Rising ocean temperatures are likely to have consequences for the Norwegian aquaculture industry: according to models based on data from the IPCC (Intergovernmental Panel on Climate Change), summer sea temperatures on the Norwegian coast will rise by an average of 1.5 oC by 2050. High summer temperatures in the sea-cages could then become a problem all along the coast, rather than just in certain regions, as at present.

“Since 2000, we have had warm summers in Western Norway. The problems this has led to may also turn up further north in the future,” says Hevrøy.

Hevrøy studied two groups of large salmon (about 2 kg) after they had spent 56 days in seawater. One group lived in water at 19 oC, the other at 14 oC. The salmon were also fed diets with different fat content. It turned out that the fish at 19 oC, which ate little, also took up very little fat, utilising instead their own reserves of fat, particularly polyunsaturated marine omega-3 fatty acids.

High temperatures thus have implications not only for growth; they can also lead to changes in product quality.

Crucial research
The study, which is published online in General and Comparative Endocrinology, was carried out in collaboration with the Institute of Marine Research, Nofima, the fish farming company Marine Harvest and feed producer Skretting. It forms the start of extensive efforts to prepare fish farming for warmer seas. Funded by a leading scientist fellowship from the Research Council of Norway, Hevrøy will work for four years on issues related to aquaculture farming at higher temperatures.

“It is vital to obtain the knowledge we need to deal with climate change,” said Hevrøy.