Each spring at the lake edges you will see signs of Sunfish spawning. The sunfish create circular ‘nests’ by fanning away debris and exposing the rocks or sand below. They aggressively defend these nests from others in the water, including humans. If you have ever been wading in the water of Truesdale Lake and been rammed in the legs by a sunfish when you get too close to their nest you will know what I mean. They look small but you will be in for a surprise when they swim into your legs.
Another spring and early summer sight is dead sunfish along the bank. Based on information from the Connecticut DEP, we can say that this is a natural part of the sunfish life cycle, affecting the weaker fish during and after spawning.
from the story here:
The state Department of Environmental Protection and the city said the problem appears to strictly involve sunfish, noting there are other fish, birds and turtles at the pond showing no ill effects. The DEP said that happens every year in New Britain and other parts of the state, to varying degrees, because it’s the spawning season for the species.
“The sunfish have a virus or bacteria when they spawn,” Parks and Recreation Commission Director Bill DeMaio said. “I’m told that they don’t eat properly and they become less healthy, just like human beings would be if you didn’t eat, and they pass the bacteria to each other.”
Fish deaths can also be caused in a number of other ways. Smaller fish can be chased into shallow water by larger predators and get stuck in weeds and unable to get free. Also, in warmer months, the oxygen levels of the lake go down as the water heats up. This causes the weaker fish to die off.
Truesdale Lake has tens of thousands of fish all different sizes. Our lake manager, Allied Biological, has said that dead fish are nothing to get alarmed about in small quantities (10+ on a typical waterfront) and are normal for lakes. However, if you notice dead fish in larger quantities (over 100) then there may be something else going on and please let us or Allied know.