Fish Health and Genetics Laboratory

Fish Health Services

The Fish Health and Genetics Laboratory at A.E. Wood Hatchery routinely tests hatchery production fish as well as those found in the wild for viruses, bacteria, parasites, and other microbes capable of causing disease in fish. Standard protocols for detecting these pathogens are adapted from accepted procedures published by the American Fisheries Society Fish Health Section and the U.S. Fish and Wildlife Service.

catfish's belly covered with reddish sores
Catfish with lesions characteristic of CCV

Largemouth bass virus (LMBV), channel catfish virus (CCV), and koi herpesvirus (due to the use of koi carp as forage at state hatcheries) are among the viral pathogens of concern. The picture at right depicts the lesions caused by CCV in channel catfish. Lab workers test for viruses by adding samples to cell cultures and monitoring for cytopathic effects caused by viral-infected cells. Effects that might be seen under the microscope include rounded cells, granule formation, vacuole formation, and formation of syncitia (giant, multi-nucleated cells).

Normal cell layer with separate nuclei Images of non-infected cell monolayer (top) and viral-infected monolayer (bottom). ©Maria-Lucia Rácz, author. Licensed for use, ASM MicrobeLibrary (
Cell layer with distorted cells

Bacteria also pose a threat to aquaculture facilities where fish are grown in high density conditions. Edwardsiella ictaluri, Aeromonas hydrophila, and Flavobacterium columnaris are just some of the bacteria that can cause problems in intensive fish culture. Parasitic worms, protozoans, and crustaceans are also of concern and are monitored for their presence microscopically.

image from microscope of P. parvum's characteristic C-shaped chloroplast
Fluorescent view of P. parvum
with the C-shaped chloroplast
that gives "golden alga" its common name

Although algal blooms often provide food for fish at the larval or fry stage, some species have recently been a problem for TPWD hatcheries, especially the golden alga Prymnesium parvum. Although this alga is not pathogenic itself, it produces toxins that can cause massive mortalities in fish ponds if not treated. Alga cell densities can be calculated using a cell counting chamber. A bioassay has also been developed to monitor the toxicity of hatchery ponds if P. parvum is detected.

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