Researchers Technique Detects Algae Potentially Fatal to
By Jim Core
December 20, 2001
Agricultural Research Service scientists
have developed a new method to detect the genetic material that algae need to
produce a fish-killing toxin. The test was developed in response to several
fish kills that occurred recently in the southeastern United States.
Scientists at the
Genetics Research Unit in Stoneville, Miss., identified the toxins and
their source. The researchers were the first to confirm channel catfish
mortalities resulting from toxin-producing algal blooms. A toxin-producing
strain of freshwater blue-green algae, Microcystis aeruginosa, was the
culprit behind the fish kills, according to microbiologist Paul V. Zimba.
Normally, M. aeruginosa produces oxygen necessary for fish
respiration and removes potentially toxic chemicals from the water. But Zimba
says some strains of this alga can produce toxins that sicken or kill fish.
To determine the magnitude of the problem, researchers took water samples
from 487 catfish farms in Alabama, Arkansas, Louisiana and Mississippi during
an 11-day period in 2000. Thirty-one percent of the ponds contained algae with
the genetic potential to produce toxins called microcystins. But less than one
percent of the ponds had toxin concentrations above the international safe
drinking water standard of one nanogram per milliliter, according to
After the researchers identified the cause of the problem, they needed a
rapid technique to determine if algae present in a given pond could produce
toxins. They developed a polymerase chain reaction (PCR) test that detects a
gene the algae need to produce the toxin. The gene is found only in
Fish production managers could soon employ the inexpensive, easy-to-use
technique to minimize the potential for fish kills by screening their
production ponds and implementing management strategies to control the algae.
The technique could also be used outside the catfish industry to detect the
presence of algal toxins in municipal drinking water, according to Zimba.
ARS is the U.S. Department of
Agricultures chief scientific research agency.