Charles Lutz, Shirley, Mark G. | 5/21/2007 11:42:25 PM
White Spot Syndrome Virus (WSSV) has been confirmed for the first time in Louisiana in crawfish. This disease seems to affect mostly medium to large crawfish. The virus can apparently cause significant losses in ponds. Symptoms include sluggish crawfish that don’t move much once they are dumped from the trap. They do not pinch hard and most cannot walk. There are no color differences or obvious signs other than weakness and slowness. Some dead crawfish are noticeable in the traps while others are noticeable in the shallow water along the edge of the pond. This viral disease affects only crustaceans like crawfish and shrimp. Humans are not susceptible to the virus, and consumption of infected crawfish does not endanger the health of humans.
Following are best managment practices regarding stocking ponds.
1. Avoid unnecessary stocking of existing ponds:
Research has shown that, taken together, crawfish population density and management of water quality and forage crops have roughly 20 times as much influence on crawfish size as genetics do. Although many producers have the idea that adding new stock to their permanent ponds will somehow improve the size and yield of their crawfish through some genetic mechanism, this is not the case. The good thing about this finding is that if a permanent pond has an established, healthy population, there is no need for supplemental stocking and the risk of introducing WSSV can be avoided entirely.
2. Obtain healthy stock:
If you MUST stock a new pond or a pond in a rice-crawfish rotation, make every effort to obtain stock from healthy ponds. These ponds should have no unusual death loss - in traps, in sacks or in the open ponds. If possible, inspect the ponds from which your stock will be acquired. Do not use crawfish from ponds showing any suspicious signs such as dead crawfish in traps, dead crawfish on the pond bottom or floating at the surface, or with any noticeable slow, lethargic crawfish inside or outside of the traps. Wild-caught stock may potentially carry the virus, but it is not possible to observe them as it would be in a pond. Because of this, it is important to thoroughly inspect wild-caught animals for signs of weakness or slow, uncoordinated movements before making a decision to use them for stocking.
3. Other stocking considerations:
Although the most up-to-date recommendations encourage crawfish producers to obtain stock from several sources to improve the chances of good burrowing survival and reproduction, this approach multiplies the possibility of encountering and stocking infected animals. If a single source of healthy crawfish can be identified, it may be best to use that source as a sole supplier for stocking. However, it is still important to follow recommendations for evaluating whether animals have the potential for good survival and reproduction. Things to look for include bright yellow fat reserves, a good ratio of females to males (preferably 50-50 or better), healthy and active behavior, and the presence of few or no white river crawfish. As always, care should be taken to minimize stress during handling by keeping crawfish wet, in the shade, and not too hot or too cold. No crawfish stored in a cooler should be used for stocking.
4. Water sources:
WSSV can be transmitted in water, to and from crawfish and other potential carriers (crustaceans and even insects) in surface waters. If you use water from canals or bayous, it is especially important to be aware of other crawfish operations using the same water resources you are. Even if you cannot be certain of what is going on in every pond that may discharge into the surface waters you use for flushing or flooding, the more information you have, the more informed your management decisions will be. If you have reason to suspect a problem, it may be necessary to test crawfish populations in the surface waters you use for WSSV. LSU AgCenter county agents, aquaculture specialists or LDAF officials can assist in this process.
Do not move traps, boats or other equipment from farm to farm (or even pond to pond within your own farm, if a problem is suspected) without taking measures to prevent the spread of WSSV. Ideally, boats should be power-washed to remove all mud and debris and then allowed to dry in the sun for a minimum of one week. Traps can simply be cleaned of mud and debris and then dried thoroughly in the sun. Alternately, boats and traps can be power washed and then sprayed or scrubbed with a 5% bleach solution.