They will school together quite a bit while as fry, particularly if a big human appears and stares at them. :) As they get older, they spread out more, but will carry on some of the schooling behavior. Once they reach maturity, they only clump together when they perceive danger or if they're trying to avoid a mating male.
The school caught my eye because they were so close together. More so than most of the minnow schools. I swept up some of the school in a net and took a look. It may be wishful thinking on my part, but they seemed to have a slightly deeper body than the minnows do and since all were of the dark variety, I'm hoping they are tilapia. I putt the fish I caught in one of my growbed tanks, where I already have some minnow fry but no bigger fish nor crawdads.
I have 4 tilapia in another growbed, but have not seen a sign of a fry in there. When I bought my fish I put 5 of the biggest in that growbed and the rest in the main tank. I lost one of them a week or so ago. Those fish are about 5 or 6 inches long now. I figured that would be where the first breeding activity would occur.
What type of tilapia do you have? Nile fry are a silvery color...rather nondescript for the first month. They grow about 1"/month, and start to show stripes color in the 2nd month.
Also, what is your PH? Tilapia breed best at around 68, with temps in the low to mid-80s, so this is a happy time of year for tilapia breeding.
My supplier said they were Niles. pH this morning at dawn shwed 7.4 on the high range and 7.6 on the low range test.
I looked again yesterday in the growbed with the 4 tilapia. No sign of any fry. They could be all the same sex as far as I know.
I'm still not sure if the little silver fry are tilapia or not as I have not seen them since I put them under my growbeds. On the other hand, I do know at least some of my tilapia are successfully breeding as i found a baby about the size of my thumbnail in my pool skimmer basket. Obvious stripes. It now resides in another growbed that has a bunch of mosquito larvae. I also put in some minnow eggs in that growbed so that fish has plenty to eat and those mosquitoes will soon be gone.