Fish Killing Golden Algae Discovered in California

Editor's Note:

There have been many recent confirmed reports of Prymnesium parvum (aka Golden Algae) infestations across the country. Prymnesium parvum (Haptophyta) is a relatively small alga that possesses two anterior flagella for mobility and a short, straight haptonema emerging from the front of the cell. This alga can photosynthesize and contains a pigment called fucoxanthin, giving it a gold coloration, though can also assimilate organic nutrients.

     The largest concern with this alga is the production of numerous toxins collectively called prymnesins. These toxins are particularly devastating to anything with gills (e.g. tadpoles, mollusks and fish) by disrupting the ability to assimilate oxygen thereby causing suffocation. Direct risks to humans and mammals have not been readily present. Exposed fish often appear to be gulping for air (despite sufficient dissolved oxygen levels) and have been observed jumping out of the water. Fish gills, fins and mouth area may appear bright red and bleeding.

     Foam may also be present with blooms of P. parvum or just a tint of gold coloration (not always as can kill fish at very low densities). Monitoring programs (microscopic identification) and early detection of these blooms is crucial in taking immediate action to control the problem and prevent additional impacts to biota in the water resource. SePRO’s analytical lab ( provides rapid identification and enumeration for golden and other types of algae.

     Some organisms impacted by Prymnesium toxins can recover if the exposure is removed (i.e. toxin source control by killing golden algae).  Operational treatments of Captain* and Captain* XTR algaecides (at low rates) are providing an effective and rapid control solution and thus preventing further fish mortalities.[p]

     Aquatechnex biologists are diagnosing the first cases of Prymnesium parvum or Golden Algae at a couple of our projects in Southern California.  This species is a tiny one celled organism with two small “tails” that can be used to move through the water column.[p]

     It was discovered in Arizona in 2005 and we have not seen it until the present in California projects. Golden Algae release toxins that affect gill breathing aquatic organisms such as fish and some shellfish.