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Submission of Fish for Diagnostic Evaluation | |||||||||||||||||||||||||||||||||||||||||||
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Because a wide variety of agents can create a range of symptoms in fish, the sooner you submit water and fish to the laboratory, the more accurate the diagnosis will be. Proper treatment can be initiated more rapidly and losses can be minimized greatly. Additionally, how that sample is handled from the onset will determine how complete and accurate the diagnosis will be. This is called diagnostic usefulness (Table 1 ). As mentioned above, live specimens are the best when identifying pathogens (i.e., parasites, bacteria, fungus, and viruses). Live fish placed on ice immediately and examined less than 24 hours later are useful specimens as well. However, in general, fish that have been dead for greater than six hours are useless for most external parasites, bacterial isolation or histology. Parasites fall off and bacteria involved in decomposition overgrow tissue as soon as the fish dies. Fish that have been frozen immediately generally lose any external parasites and histology of tissues is impossible. However, frozen specimens are useful in determining bacterial or viral pathogens. Fish fixed in 10% buffered formalin are best utilized for histological evaluations, however, tissue sections must be appropriately sized to fix properly. Table 1: Diagnostic usefulness of specimens for identifying pathogens. How the sample is handled will determine how complete and accurate a diagnosis will be. Specimens labeled "dead" are those that died within 12 hours. Specimens labeled "iced" or "frozen" are those animals that were moribund and placed on ice or immediately frozen for transport. Fixed tissues are from live fish immediately placed in 10% buffered formalin. This table is modified from Noga, 1996.
Summary: When a fish becomes sick or dies, it is important to respond correctly to determine why the fish's health is compromised. Know your system by keeping good records of water chemistry parameters, water changes, and recent changes or additions of fish. This will help when speaking with a fish health professional and will facilitate the process of making an accurate diagnosis. Separate water and representative fish samples are usually required by the diagnostic facility. How the samples are collected and shipped will determine their usefulness in the examination and consequently the accuracy and effectiveness of the final assessment and recommendation. References: Noga, E.J. 1996. Fish Disease. Diagnosis and Treatment. Mosby-Yearbook, Inc., St. Louis, MO. more ... |
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