Enzyme-Linked Immunosorbant Assay (ELISA)
Enzyme-Linked Immunosorbant Assay (ELISA) is a type of test used to detect the level of antigens for Renibacterium salmoninarum, the causative agent for Bacteria Kidney Disease (BKD). Although BKD is native to waters of the Pacific northwest states, it can cause health problems and high mortality rates in salmonids, especially Spring Chinook Salmon. It can occur as an acute outbreak with many losses, or it can be chronic with low levels of mortality rising with stresses and other pressures on fish. In a hatchery setting, these stresses are intensified. The disease can be horizontally transmitted from fish to fish via the water, or it can be vertically transmitted, from a female to her eggs. Once a fish has BKD, it is very difficult for the fish to overcome or be cured, since the R. salmoninarum bacteria can reside, still alive, inside the fishs immune cells. The antibiotic Erythromycin is often used in medicated feed under an INAD and can decrease mortalities, but will not rid the fish of the bacteria. Some hatcheries inject female adult Chinook salmon with Erythromycin before spawning to help decrease the likelihood of vertical transmission to the eggs.
Fish Health Center (CA-NV FHC), as well as many other fish health centers
and labs, ELISA is used to help manage BKD in fish. Fish health biologists
randomly sample kidneys from steelhead and Chinook salmon during spawning
at Coleman National Fish Hatchery, which is co-located with CA-NV FHC. In
addition, samples are collected at pre-release examinations, or "pre-libs"
to assess the level of bacteria before the fish are released from the hatchery
for migration to the ocean. ELISA is also used to monitor the levels of
R. salmoninarum in trout and salmon as they are raised in other federal
fish hatcheries, as well as in wild fish, part of the in National Wild Fish
Health Survey, in our service areas of California and Nevada.