Red Tide and Fish Hatcheries

Jennifer Butler | Hatchery Biologist, Sea Center Texas
Red Tide and Fish Hatcheries
Karenia brevis at 40x magnification.

If you spend time fishing the Gulf coast you have probably at least heard the term, "Red Tide." Maybe you have even suffered from its toxic effects. "Red Tide" refers to a dinoflagellate bloom of huge proportions. A dinoflagellate is a single cell phytoplankton, or "drifting plant." The species that causes red tide in the coastal waters of Texas is Karenia brevis (abbreviated to K. brevis, Figure 1). These dinoflagellates are very small, so small that they are undetectable to the naked eye. Two hundred K. brevis cells lined up side by side would fit in the period at the end of this sentence.

Under the right conditions, they will reproduce rapidly and form a "bloom." A K. brevis bloom is very visible to the naked eye, and gives water a brownish-red tint. These blooms can get so large and stretch so far across bays and in the Gulf that you cannot see the extent of the bloom from an airplane. They can be miles long and are moved by tides and currents.

While most phytoplankton blooms are common and harmless, there are a few species that are toxic. K. brevis is one of the toxic dinoflagellates. They produce brevetoxin, a potent neurotoxin. It affects humans in two ways. Neurotoxic Shellfish Poisoning (NSP) occurs when a human eats a shellfish, like an oyster, and gets sick. The oyster is a filter feeder, and consumes K. brevis when filtered from the water. The brevetoxin is not neutralized even when the oysters are cooked thoroughly, so it is important to know if there is a bloom in your area. Symptoms can include gastrointestinal problems, nausea, vomiting, dizziness, slurred speech, numbness of lips, mouth and tongue, and respiratory distress. Another way that humans are affected is when the brevetoxin is aerosolized. This occurs when there is a bloom and windy/rough sea conditions. Waves agitate the dinoflagellates breaking them up and releasing the brevetoxin into the water. The wind picks up the toxin-containing aerosol and disperses it. Breathing the toxin can cause coughing and sneezing and could be problematic to people who suffer from respiratory asthma. Brevetoxin affects fish by paralysis causing death. Red tide has been linked to massive fish kills along the Texas coast (although not all fish kills are caused by red tide), and fish hatcheries are not immune to its effects.

So, how does this tiny dinoflagellate impact at Sea Center Texas (SCT), TPWDs largest marine hatchery? Well, SCT is positioned near the coast and pumps natural seawater through a pipeline from a pump station. The facility utilizes this resource in everyday operations by filling outdoor fish rearing ponds, broodfish tanks, and aquarium displays. A red tide bloom in close proximity to the seawater intake station could cause serious problems. Fortunately, we are prepared for such an event.

Sea Center Texas has an 8-acre reservoir that serves as a seawater storage site. The facility can be operated in a scaled-back manner until the bloom dissipates or disappears by using seawater from the reservoir. The last red tide event that impacted operations at TPWD's Coastal Fisheries began in September of 2011 and tapered off in the early spring of 2012. This was the longest red tide event recorded. In addition to local and regional sampling by Coastal Fisheries during the bloom, Sea Center performed daily K. brevis counts from water samples taken from our intake station and our reservoir. This enabled us to be very proactive with water management: mission critical systems were prioritized, seawater discharge was minimized, and fingerling grow-out in ponds was coming to its seasonal end. Although red tide induced fish kills occurred at our intake pump station, nearby beaches, bays, and marshes, SCT experienced no fish mortality.

Certain combinations of environmental conditions trigger red tide blooms but the exact cause remains unknown. In the meantime, Coastal Fisheries staff are keeping a watchful eye on the color, smell, and phytoplankton composition of our Texas coastal waters.

To report a fish kill, or if you suspect a red tide bloom, call TPWD's 24-hour communications centers at (512)-389-4848 (Austin) or (281)-842-8100 (Houston). For more information about red tide and the latest updates, call the TPWD hotline at (800) 792-1112, select fishing, and then select red tide. Current information about shellfish closures can be obtained by contacting the Seafood Safety Division of the Texas Department of State Health Services at (800) 685-0361. (Save these numbers in your phone so you can call when you are on the water.) More information, including downloadable and printable brochures, can be found at and searching "red tide."

For more information about Sea Center Texas, visit, find us on Facebook, or call (979) 292-0100 ext. 21.