“We have been unable to detect injuries to salmon resulting from the fish being exposed to low pressure during vacuum pumping,” say Nofima scientists, who have studied the effect of vacuum on salmon.
The use of vacuum/pressure pumping when fish are moved to sea cages or a well boat for harvesting is common practice. The pumps comprise of a tube with a tank in the middle. The tank changes between negative pressure (vacuum) and positive pressure in order to alternate between sucking the fish from the sea cage and pushing it from the tank over to, for instance, a well boat.
Blood in the pumping water
During vacuum pumping of salmon in the industry, blood has on occasions been observed in the pumping water. The blood generally originates from the gills or other wounds on the fish. Nofima, in collaboration with the Institute of Marine Research, has researched whether this may be attributed solely to the vacuum in the pumping process. In order to study whether vacuum alone may be a possible explanation of the blood in the pumping water, a study was carried out in February 2010 involving anaesthetised and non-anaesthetised Atlantic salmon.
No injuries detected
“In the trial we saw no sign of blood in the anaesthetic tank after the vacuum treatment. Further, no injuries were observed in the organs, muscle or inside the belly,” says Scientist and Project Manager Åsa Espmark.
“We think the blood which from time to time is detected in the pumping water comes from injuries that the salmon sustain from bumping into each other. This may also come from knocks inside the pump unit.”
Espmark says that the measurement of physiological stress pointed to salmon suffering from little stress. However, salmon that were exposed to medium and high vacuum challenge released more air (belched) than salmon exposed to low vacuum. The control fish did not release air. However, it is worth noting that all vacuum pumped salmon release some air - even at low pressure. The salmon in the trial with the medium and high vacuum challenge also swam even more than the other fish, resulting in an increased respiratory rate. The degree of air release and the time the salmon spent swimming increased in line with the vacuum challenge, but the respiratory rate was high in all vacuum pumped salmon.
The project is financed by the Fishery and Aquaculture Industry Research Fund (FHF). The report below contains supplementary explanations of the measurements and tests carried out during the trial (in Norwegian language only).
In the trial, the salmon were exposed to vacuum and pressure for different lengths of time. The trial involved anaesthetised and non-anaesthetised salmon.
“Under vacuum, we checked for blood in the water using visual inspection through the cylinder. We also took samples of the water before and after using multistix.”
“Blood was not detected in the water, either visually or using multistix, for any of the vacuum pumped salmon or in the control group. Further, no blood or injuries were detected in the inner organs during dissection,” the scientists conclude.
All the anaesthetised salmon awoke after 1 - 4 minutes and started to swim in the observation tank. Further, no sign of deviation from normal behaviour was observed in relation to the control group. No mortality was observed in the following six-week period.
“We conclude that vacuum in itself can probably not explain blood and injuries observed during pumping, but that some injuries are possible after pumping of large quantities of salmon on an industrial scale,” says Espmark.
Nofima followed up the study on anaesthetised salmon with a trial on free-swimming non-anaesthetised salmon. The scientists wanted to study any behavioural changes that resulted from pumping, and study physiology when the salmon is subjected to stress.
“We did not register any large differences between individual groups relating to physiology or morphology,” says Espmark. On the contrary, there were significant differences in the swimming activity and belching between the groups.