Those appear to be fish eggs and if you have any corydora catfish in the tank, most likely theirs. You might get lucky and they hatch and you get more of whatever you already have or your other fish will eat the eggs which is good protein for them. But just to rule out other possible fish, what species do you have in the tank?
At least 1 of them is female then, possibly both. They dont need a male to lay eggs, but you need a male and female snail and brackish water for them to hatch.