Transportation of fish involves capture, loading, transport, unloading and stocking and so can induce large stress responses from which the fish will take a long time to recover. Poor conditions during transport, such as overcrowding and inadequate water quality, can cause irreparable damage to the fish and even death.
In 2004, the EU’s “AHAW” panel published a report on the welfare of fish during transport1. In the EU, there are five main methods used to transport fish, of which tanks and plastic bags are probably the most commonly used:
- well-boats (boats with a well in which to keep fish alive)
- towing of cages by tugs
- helicopter transport of open bins
- insulated tanks and sealed plastic bags in insulated boxes.
Fish transportation exposes fish to a range of stressful stimuli during transport:
- during pre-transport treatment (e.g. draining of ponds, pre-transport starvation to clear the gut)
- during loading (e.g. netting the fish) and
- during the journey (e.g. inadequately maintained water quality leading to low oxygen levels and build up of CO2 and excretory products).
Fish have a stress physiology which is directly comparable to that of mammals and birds2 and stressful stimuli have been shown to produce a wide variety of effects on transported fish such as metabolic hormonal and behavioural alterations. Immunosuppressive effects and osmoregulatory problems can activate latent disease organisms and are the major cause of death when fish are handled and transported.
It has been shown for a number of species, that the initial loading of fish into the container is the most stressful component of transport. The skin surface of all fishes is extremely delicate and fish can suffer damage from netting, which is the most widely used procedure for this. Use of pumps and transfer in water pipe systems can greatly reduce skin trauma and cortisone levels associated with such transfer.
Lowering the temperature under which fish are transported increases the stocking density that the fish can tolerate, since lower temperature slows the metabolism (reducing oxygen requirements), but abrupt temperature changes are stressful to fish. The temperature changes to which fish are exposed during transport are highlighted as a major fish welfare problem during transport in a stakeholder forum organized by the Humane Slaughter Association3, as were the transfer of smolt to seawater before they are capable of coping physiologically, and mechanical breakdowns, which result in “significant mortalities” during transport.
Anaesthetics can help reduce stress but none are currently licensed in Europe for food fish. The use of anaesthetics and other welfare related compounds in the EU is currently greatly constrained by drug licensing arrangements which make low cost compounds unavailable owing to the high cost of licensing of all veterinary therapeutics.
Some species, such as pangasius, carp, tilapia and eel, are routinely transported by land without water. Though these species are able to survive such conditions, they are likely to be very stressed by lack of oxygen, by physical vibration, pressure and temperature4.
The World Organisation for Animal Health (OIE) has published welfare guidelines for the transport of fish.5 A fully referenced discussion of the welfare issues in fish farmed is available in the following paper:
Study to estimate numbers of farmed fish killed in global aquaculture each year ( 540 KB) 40 pages. July 2012.
1. Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to the welfare of animals during transport. The EFSA Journal (2004) 44, 1-36. http://www.efsa.europa.eu/en/efsajournal/doc/44.pdf.
2. Scientific Opinion of the Panel on Animal Health and Welfare on a request from European Commission on General approach to fish welfare and to the concept of sentience in fish. The EFSA Journal (2009) 954, 1-26. http://www.efsa.europa.eu/en/efsajournal/pub/954.htm.
3. Fish Welfare During Transport. Forum organised by the Humane Slaughter Association. 25 October 2006. Thistle Hotel, Inverness. http://www.hsa.org.uk/Resources/Fish%20Transport%20proceddings.pdf.
4. Lines, J.A. and Spence, J., 2012. Safeguarding the welfare of farmed fish at harvest. Fish Physiology and Biochemistry. Volume 38, Number 1 (2012), 153-162, DOI: 10.1007/s10695-011-9561-5.
5. Chapter 7.2. Welfare of farmed fish during transport. http://web.oie.int/eng/normes/fcode/en_chapitre_1.7.2.pdf.