TOXIC ALGAE MONITORING ON ARKANSAS CATFISH FARMS

In recent years, catfish farmers in southern Arkansas have experienced fish kills not attributed to infectious diseases or low dissolved oxygen in ponds. Farmers have described erratic behavior of catfish just below the pond water surface (typically starting in the early afternoon) when water quality is stable and there are no other signs of disease. Certain characteristics of these unusual losses are similar to known fish mortality events that have been associated with toxic algae. Many algae produces toxins that may cause fish kills, including species of blue-green algae, golden algae, and eugenoids.  One species, Prymnesium parvum, has caused large fish kills in brackish water rivers and lakes in Texas, and is of interest because some catfish ponds in Arkansas have moderately mineralized water that might support Prymnesium blooms.".

Starting in May 2015, weekly algae samples were collected by extension personnel at two Arkansas catfish farms (total of 64 ponds). Algae samples were evaluated weekly for dominant species at the UAPB Lake Village Lab from May through November. Samples were not collected in the winter. Blue green algae of interest included suspected toxin-producing species of Planktothrix Anabaena, Microcystis, Spirulina, as well as Prymnesium. At esach sampling 10 ml of sample was frozen weekly for Abraxis microcystin test strip analysis if needed (used only in the event of a toxic algae fish kill). The monitoring program is currently ongoing.

Species of Planktothrix, especially the known toxin-producer  P. agardhii, were the most common algae present in foodfish ponds from July through November.  Other known toxin-producing species in the genera Microcystis and Anabaena were also present, but in much lower numbers.  Despite the frequent occurrence (often throughout the study in some ponds) of known or suspected toxin producing algae, no toxic events occurred in the 64 ponds studied in 2015 (Figure 1).

The study is being continued in 2016 and will conclude in November of this year.