Post-Freeze Fish Mortality

Residents of Fort Bend County MUD No. 118 may have noticed that the recent freezing weather has caused some non-native fish species to die. The species impacted most were primarily Plecostomus and Tilapia. Both species are non-native tropical fish which have a significantly lower tolerance of prolonged exposure to low water temperatures compared to native species of fish. As water temperatures drop, their metabolism slows, and immune system becomes weakened. Once this happens, the chances of these fish expiring increases significantly. Even as air temperatures rise into the 70s, water temperatures can remain in the 50s. This prolongs the stresses of cold temperatures on the fishery resulting in fish succumbing to the elements several days after the freezing weather has ended. This is referred to as delayed mortality. Because of this delay, observers are often confused by the timing of the deceased fish’s appearance at the surface.

To alleviate this nuisance, the District is working to remove as many deceased fish from the lake as possible, but unfortunately not all fish will surface at the same time and park goers will continue to see deceased fish in the lake and along the lake shore until all fish of susceptible species have surfaced.