Submission of Fish for Diagnostic Evaluation
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Submission of a Water Sample
Fish spend their entire life in water, which means when a fish gets sick, that environment must be tested. No matter how clean you think your water is, no matter what your water source is, and even if your system is flow-through, you must have recent records of your water quality parameters (e.g. temperature, pH, ammonia, nitrite, dissolved oxygen) and submit a water sample for analysis. A good diagnostic laboratory will first test the water for any deviation in quality.

When submitting a water sample for analysis, a few simple yet important procedures must be followed. First, water should be sampled as soon as the fish begin to act abnormally and before water changes are initiated. A clean container (approximately one quart), thoroughly rinsed of any foreign matter or soap residue, should be used. If the system in question is a pond, it is important to submerge the container under the water and place the cap on the container beneath the surface. This removes any air bubbles, which could interfere with the dissolved oxygen measurement. (Ideally, dissolved oxygen and temperature should be measured at the pond, and if the pond is large, at multiple depths and locations.) If there are multiple systems involved, samples from each will be needed. In cage culture, water should be sampled inside the cage as well as outside the cage.

The water sample should be separate from the fish sample. The water that the fish are brought in will not correctly reflect what is occurring in your system. The chemistry of the water, which includes pH and ammonia, will change remarkably during transport. For example, while the fish is being transported to the diagnostic laboratory, its metabolic activities (i.e., respiration, excretion) will cause the pH to decrease and the ammonia to increase in the shipping water.

It is important to label all samples with pertinent information, such as client's name, sample location, depth, and the time of collection. Keep the water sample in cold storage once collected. When shipping water, place the sample on ice or ice packs. A Styrofoam® cooler in a cardboard shipping carton works well for shipping overnight to a diagnostic facility.

Submission of a Fish Sample
The best fish samples for diagnostic evaluation are the fish that are near death (moribund) or showing signs of distress. Dead fish are rarely acceptable for diagnostic tests. However, if the fish are in good condition, that is, their eyes are clear and the gills are red, they may have some value. If they are obviously decomposed or malodorous, do not submit them. It is also important to submit a representative number of each species involved. Usually three to five fish will be sufficient. This ensures an accurate diagnosis of the population as a whole.

If the fish are alive and appear to be able to make the trip to the laboratory, place them into well-aerated water in a heavy ply plastic bag (fish shipping bag or commercial freezer bag), and a Styrofoam® cooler to regulate temperature. This can then be placed in a cardboard shipping carton and shipped overnight. If the fish are dead or will not make the transport, the fish should be kept moist with wet paper towels in a heavy ply plastic bag. Keep the sample cold packed with ice in a Styrofoam® cooler and shipping carton. It is important not to freeze the sample, especially if tissues are to be submitted for histopathology (examination of tissues for disease processes at the microscopic level).

There are commercial overnight carriers that will take live and dead fish, if they are properly packed as mentioned above. Also, most diagnostic facilities require prior notification that a sample is being shipped to their laboratory. This ensures a contact person will be there to receive the shipment and be able to start work on it in an expedient manner. Listed in the appendix are a number of laboratories in Florida that are qualified to diagnose fish diseases. Contact the one closest to you for further information.

Samples that are hand delivered to a laboratory should also be properly transported. Notify the laboratory you are coming with the sample. Keep live fish in a bucket with a battery-operated aerator or a plastic bag with well-oxygenated water, and moribund/dead fish wrapped in wet paper towels in a plastic bag on ice in a cooler.

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