Algaecide offers new way to fight off-flavour in catfish

Catfish farmers made sad and blue by blue-green algae that cause 'off-flavours' in their fish may soon get some relief. Agricultural Research Service​ (ARS) scientists in the US claim to have discovered a natural-based algaecide that not only kills the algae in fish ponds, but is also safer for other pond life when compared to current treatments.

The researchers say that the algaecide - currently the subject of a patent application - uses a product derived from a compound found in ryegrass. It was discovered by researchers led by microbiologist Kevin Schrader at ARS' Natural Products Utilization Research Unit in Oxford, Mississippi in the US, in collaboration with biochemist Dhammika Nanayakkara at the University of Mississippi's National Center for Natural Products Research, also in Oxford in the US.

The research targeted a species of blue-green algae prevalent in Mississippi, home to half of the US's catfish farms. This algal species produces a musty compound that can be absorbed by the catfish, giving them a 'muddy' type of off-flavour.

The researchers explain how currently, catfish farmers choose between two chemical treatments for the €46.5 million-per-year problem: copper sulphate, the only US Environmental Protection Agency-approved algaecide for such use on a permanent basis; and diuron, a chlorine-based herbicide that can be used only with government permission on an annual basis. Both of these treatments can be toxic to most phytoplankton, including green algae that do not cause off-flavour.

In laboratory tests, the algaecide was reportedly 40 times less lethal to green algae than diuron. The researchers also noted that it rapidly dissipated from pond water within hours, whereas diuron can be detected for weeks after application.