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Fish Handling and Transport 1
Michael McGee and Charles Cichra2See Figure 1 .
Whenever fish are stressed during handling or transport they become vulnerable to injury and disease. Fish farmers know that fish will often "breakdown" if they are handled poorly and for this reason, proper care during harvest and transport is important. Although most fish farms have established procedures for handling fish, it pays to remain aware of what situations can later lead to fish disease outbreaks and mortality.
Figure 1 . Causes of Stress
Fish, crowded in a trap or net, can rapidly deplete the oxygen supply in a localized area. In warm water oxygen is less soluble and fish respiration is higher. Sublethal oxygen stress often leads to later disease outbreaks.Fish which get scraped or bruised during handling can lose their protective slime coating, thereby reducing their natural defense against pathogens (viruses). Loss of scales or cuts are even a more dramatic invitation to infection or direct mortality due to injury.
Sudden water temperature changes are a well known cause of fish stress. Try to avoid direct water temperature changes of greater than 5 degrees Fahrenheit when moving fish from one environment to another. If large differences in water temperatures exist, then gradual tempering to acclimate them is important. Fish can be acclimated to a 10 degree Fahrenheit change in about 20 minutes by slowly mixing waters to equalize temperature.
A sudden pH shock may also be harmful, especially to young fish. Within the range of pH 6 to 9, a pH shift of less than 2 units can be tolerated by most fish. If a large difference in pH exists water can be mixed to gradually acclimate fish.
When possible, it is better to harvest and move fish during the cooler parts of the day, and avoid long exposure to strong sunlight. Avoid leaving fish in the sun if they are in small containers, as the water will warm quickly.
Useful Techniques to Reduce Stress
Either aeration or pure oxygen supplied to hauling tanks can help prevent oxygen stress and allow more fish to be safely transported. Water in hauling tanks should be kept cool and clean. Some medications may be added to the water to reduce risks of infection. Salt at 0.5% is sometimes added to increase the tolerance of fish to handling.Small fish are usually more sensitive to handling and environmental stress than larger ones. For this reason, special precautions should be taken when transporting or stocking fry.
Fish harvested from ponds and moved to indoor holding tanks often carry parasites and disease organisms with them. As a result of the stress of handling and the crowding of fish into vats, the fish's resistance is lowered and a disease outbreak may occur. As a preventative measure, fish are often given a prophylactic treatment shortly after they have been brought in. Common treatments include a 2 hour bath of potassium permanganate at 3ppm (mg/l), or a 1 hour formalin bath at 50-100 ppm (mg/l). These treatments will eliminate most external parasites, however, when using them for the first time it is important to be certain the dosage is not too stressful to the fish. If a bacterial disease is anticipated, bath treatments with antibiotics for 4 to 8 hours can be used. Most antibiotics are banned for use on food fish but several useful ones remain available to ornamental fish farmers.
Occasionally, as a result of severe stress during harvest or transport, fish will become sick and not respond to treatment. If this appears to be the case, the best solution is often to return the fish to the pond. Sometimes, although losses will occur, many fish will recover in the pond.
Summary
Experience and observation are the best teachers when learning how to avoid stressing fish during handling and transport. Since the outcome of poor handling is generally sick or dying fish it does not make sense to take chances. Establish and follow a set of procedures which minimize stress and risk of injury to fish when they are handled. Use appropriate preventative treatments to ward off disease outbreaks before they occur. Look for patterns in the type and extent of diseases which occur when compared with the type of handling the fish have received and under what conditions. Placing an emphasis on following these useful guidelines should help prevent disease problems and unnecessary losses for fish farmers. (See Figure 1 )
Footnotes
1. This document is FA3, one of a series of the Fisheries and Aquatic Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May, 1997. Reviewed July, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu.2. Michael McGee, former assistant professor, extension aquaculture; Charles Cichra, associate professor; Department of Fisheries and Aquaculture, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
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