Fish kills happen in Florida. They are alarming and can be a major turn off to prospective new home owners, board members and residents. Read on to learn why fish kills happen.
In Florida, low dissolved oxygen levels are by far the most common cause of fish kills and usually occur in the warmer months from May through September. Fish swimming near the surface of the water, and appearing to be gulping for air indicate a low oxygen problem. Low dissolved oxygen levels in a body of water can be caused by many factors including high summer water temperatures, highly organic bottom muck, dense plankton algae blooms, and intense tropical rainstorms flushing in organic debris with extended cloudy weather conditions.
Turnover occurs when surface water mixes with water near the lake bottom. The bottom water may contain little or no oxygen and have high concentrations of toxic gasses like carbon dioxide and hydrogen sulfide that are potentially lethal to fish. Turnover in Florida lakes happens naturally each Fall as the season’s first strong cold front in October or November lowers surface water temperatures rapidly and strong winds combine to mix the water column.
Storm water run-off high in organic content and chemicals creates a spike in dissolved oxygen demand that can quickly lower lake oxygen levels and raise ammonia, nitrogen and turbidity enough to harm or kill fish populations. Sometimes recently applied fertilizer, pesticides and asphalt sealers in watershed runoff are directly toxic enough to cause a fish kill.
A rarer cause of fish kills is a bloom of golden algae which releases a toxin that suffocates fish. As the name suggests, Golden algae are not green in color and the blooms are generally not readily noticeable to the human eye. A quick microscopic algal identification by a trained biologist can determine if Golden algae is behind a recent fish kill.
Florida fish are just like us. They are acclimated to warm temperatures. In the winter, temperatures are rarely below 50°F (10°C) for more than a day or two so when cold snaps that hang around drop the water temperature below about 55°F (13°C) nearly all our non-native tropical fish species are stressed. Tilapia, peacock bass and other cichlid species are particularly vulnerable to cold temperatures. Any fish species can be stressed by temperatures that drop more quickly than about 1°C per day. Both native and exotic fish will not survive if the cold weather stays around too long.
Unfortunately, fish are as vulnerable to disease as other wildlife and sometimes a pond or lake experiences a natural widespread fish kill caused by a disease. Although less common, disease should be considered especially when only one species of fish in an otherwise healthy lake is dying.
Fish kills do happen but with a proactive approach to lake management there are proven steps to take that help prevent kills from occurring. Environmentally sustainable lake management planning provides solutions that greatly improve water quality benefiting your fisheries, so they reach their full potential.