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Biology of Golden Alga, Prymnesium parvum

What Is Prymnesium parvum?

Golden Alga (<em>Prymnesium parvum</em>)
Golden Alga, Prymnesium parvum
Drawing by Robert G. Howells, TPWD

Algae are primitive plants that are usually aquatic and lack true stems, roots, and leaves. Prymnesium parvum, the golden alga, is a one cell (microscopic), flagellated member of the haptophytes. It has two hair-like flagella used to swim through the water. There is also a shorter stiff hair-like structure called a haptonema. The haptonema can be used to attach the cell to objects. The cell has a C-shaped chloroplast that wraps around the middle and is where the yellow-green color is seen. The nucleus is clear and cannot be seen under a microscope without adding stains to color it. Often there are round shapes in the bottom of this alga because the cell can pull inside and digest bacteria and other algae.

We do not know if this alga is native and not identified before the 1980s or if it is an invasive species accidentally introduced to North America. Little is known about the environmental requirements of this alga or what allows it to gain a competitive edge over other species and bloom. An algal bloom is an explosive increase in the plant population numbers of one or several alga species.

What we know about the toxins

The golden alga (P. parvum) releases at least two chemical compounds that combine with cations (positively charged elements such as magnesium [Mg++] and calcium [Ca++]) in the water to make toxins. The type of toxin created is dependent on the water chemistry. Usually there is a combination of toxins in the water. The toxins cause exposed cells (cells without protective layers such as on the surface of gills and fins) to fail. Excess water and waterborne chemicals are allowed inside the cells and eventually inside organism. These exposed cells either die due to chemicals or break open due to excess water.

How golden alga uses the toxins

Golden alga can ingest (eat) other cells. Researchers think that the toxins are used to slow down prey (bacteria and other alga), making it easier for the golden alga to catch and eat them. In fish, the first damage is to the exposed skin and gill cells. The outer layer cells are damaged, then the next cell layer is affected, and so on. Soon the gills are so badly damaged that they are unable to function, and blood vessels in the gills leak into the water (hemorrhage). At the same time, the toxins and other waterborne chemicals are entering into the circulatory system of the fish, and internal organs are damaged. Bleeding also occurs in exposed areas like fins. Fish behave as if there is not enough oxygen in the water. They travel at the top of the water surface or rest on the bottom in edges and shallow areas.

Unlike toxic red tide blooms on the coast, golden alga toxins have no apparent lethal effect on non-gill breathing organisms. Cattle, predators, scavengers, birds and other animals have been observed drinking water during a bloom, and many eat the dead fish during on-going golden alga fish kills with no apparent effects. The golden alga toxins are acid-liable, meaning they breakdown in acidic conditions, such as in the stomach. Researchers believe this is why animals are able to drink the water and eat affected fish without having toxic effects. Also, terrestrial animals have skin layers to protect them; these same layers protect them from the toxins. Officials from the Texas Department of State Health Services have stated that the golden alga is not known to be a human health problem, but people should not pick up dead, or dying, fish for eating.

Impacts of Blooms

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Aditional Information:

Would you like to know more?
The Biology of Golden Alga summarizes what we know about the alga and its toxins.

Where does golden alga fit compared to other single-celled organisms?
The Golden Alga Family Tree gives examples of and information about golden alga and other protists.

What does golden alga look like?
TPWD Golden Alga Images has photos of fish kills, golden algal cells, and short videos of live golden alga. These images may be used for noncommercial/educational purposes as long as TPWD is given credit and other site policies are followed.

Golden Alga Information Card: TPWD has collaborated with the Texas Commission on Environmental Quality and other entities to produce a golden alga information card. Download a PDF from the TCEQ website or request a free hard copy from TPWD at

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