Last week, I was called to look at the first fish kill this season. This is a small 1/2 acre pond surrounded by trees. It is spring fed and no agriculture around. Different species of bass and bream were found dead the next morning. The fish kill happened overnight and is a result of low oxygen levels in the water. We know this is the case when larger fish die first, and lack of oxygen would affect larger fish before small fish. When temperatures are this high and we see cloudy days/nights, the lack of oxygen in the water from photosynthesis causes these kills.
We had a pond management program yesterday where UGA Extension Aquaculture Specialist Dr. Gary Burtle addressed this issue. He said historically, he would not necessarily recommend an aerator in every pond. However, he now recommends most ponds have some type of aerator. They can be expensive, but by the time you put the money into production of fish, losing them is more costly. The pond I visited was surrounded by trees were air could not get to it. It has been very hot and this is a factor in fish kills. We can also see fish kills after rain. Here is what Dr. Burtle has to say:
“The usual reason for fish death after rains is a partial oxygen depletion caused by the influx of water which has no algae in it or a high concentration of bacteria in it. When algae are replaced by bacteria, the water turns brown in color and oxygen concentration drops. Bass are larger than bream, so may be affected first. The oxygen stress may cause the fish to become susceptible to disease, so fish deaths may occur for several days after the partial oxygen depletion.
When the pond begins to ‘green up’ again, oxygen concentrations will increase and fish deaths stop. Until oxygen concentration returns to normal levels, low oxygen each morning or during cloudy weather may cause more fish stress and death. The solution is to install an aerator and operate during cloudy weather, which seems to be more prevalent in Georgia in the late summer and fall.”
We had a great turn out at our pond meeting yesterday. Below is a photo of Dr. Burtle going over common weed species in ponds: