Hello; A few years ago, around 1968 or 69, while an undergraduate I was in a stream in north west KY. I had found a small pool near there with lots of daphnia. I saw a black ball slowly rolling along in the stream that varied in size from that of a volley ball to near a basketball. From a distance it seemed very odd. I went closer and discovered it was made of many small black catfish. They were somehow and for some reason staying together in a ball shape as they moved along in the water. I had my daphnia net with me and a small bucket so I scooped up a couple.
The ball of small catfish maybe an inch or so long kept on downstream. It would change shape at an obstacle but was generally ball shaped. I have never seen this again but it is one of those memories that has stuck for over 50 years.
