When fish are transported they go through a series of stressful stages. Firstly fish are fasted in order to prevent vomiting during transportation and to remove any flavours from the flesh. Next, fish are crowded in preparation for the journey and then fish are loaded, transported and unloaded again.
As all these stages can be stressful to fish, Mr Van de Vis said it is therefore important to understand and reduce the stress inflicted. This is not only beneficiary to fish welfare, but it can also improve fish meat quality, as the study showed.
To carry out the experiment, Mr Van de Vis transported market size European eel and African catfish on a three hour round trip. The fish were transported in commercial haulers and left and returned to the same farm so their stress levels could be monitored.
During transportation, catfish were exposed to a fall during loading/unloading as they were dropped into water. Mr Van de Vis also noted that eels had added oxygen during transportation whereas catfish did not.
In order to analyse stress levels, total ammonia nitrate (tan), temperature, oxygen, nitrate and pH levels were all monitored.
After transportation, catfish tan levels did not exceed normal levels. Temperature varied between 18-22ºc. Nitrate levels however were below expected. No increase was seen in plasma glucose, meaning energy metabolism was unaffected.
Levels of cortisol, which is released in response to stress, in the catfish also increased to above 50 ng/ml, but the fish recovered to baseline levels after 48 hours.
Some skin lesions were identified due to the falls and therefore Mr Van de Vis advised not to allow the fish to fall and instead to ease fish more gently into water.
In the eels, mild cortisol changes were identified and after six hours these levels were back to the baseline level.
There was also an increase in plasma levels of non-esterified fatty acids that lasted for 72 hours, showing an increase in energy metabolism.
In conclusion, Mr Van de Vis said that the results proved that transportation does cause stress to fish. Although cortisol levels were raised they did return to baseline levels.
AQUA 2012: Measuring Fish Stress Response to Overland Transportation
Fish are constantly being moved and transported, having both an affect on their health and on their meat quality. Hans Van de Vis, from the Netherlands Institute for Marine Resources & Ecosystem Studies has looked at the stress response in farmed African catfish and European eel to overland transportation, writes Lucy Towers, TheFishSite Editor, at AQUA 2012, Prague, Czech Republic.
by Lucy Towers
