More than 10 years ago, during a prolonged drought, a number of major catfish kills occurred that were attributed to a toxin released by an unusual species of blue green algae. “We are in a drought again and are seeing some fish losses that we attribute to the algal toxin,” says Larry Dorman, a University of Arkansas at Pine Bluff Extension aquaculture specialist. “Thus far, we are aware of four ponds that have experienced near total losses.”
This algae grows most commonly in ponds with moderate amounts of salt, 300 parts per million chloride and higher, he says. It grows into a dense bloom and suddenly dies, releasing a toxin that kills catfish.
“In a typical situation, the farmer reports that the fish were feeding well one morning and then on the same afternoon or during the next day, a whole pond of fish starts to die,” Dorman says. “The whole cycle from healthy fish, through fish kill, and back to no sick fish can take as little as one day.” In extreme cases, losses can be as high as 100 percent in a pond. During the winter and spring of 1999 – 2000, more than two million pounds of catfish losses were attributed to algal toxins. Fish losses stopped once the spring rains started and then did not reoccur for the next several years.
“If you have ponds in the saltier water areas of Chicot, Desha or Ashley counties, you need to collect water samples weekly and submit them to the UAPB Fish Disease Diagnostic Laboratory in Lake Village,” Dorman says. Laboratory personnel will examine the water samples microscopically, determine the problem algal population and make the appropriate recommendation concerning the problem algal species. This may include treating the pond with the appropriate algicide to “thin” the algal population.
“If the problem algae are allowed to develop, die and release the toxin, major changes in your fish’s behavior will occur,” Dorman says. “You will see your fish skimming at the surface and actually try to come out of the water up on the pond’s levee. If this occurs, you have probably waited too late for any treatment to be successful.”
Producers who have ponds in the “high salt” areas should contact the UAPB Lake Village Lab and enroll in the algal monitoring program, Dorman advises. The lab serves fish producers and recreational pond owners by providing fish disease diagnosis, fish health inspections, water testing and more. For more information, call 870-265-5440.