A crayfish has one heart that contains two chambers
One pair
they have 2 i think
The female gives birth to two to eight cubs.
Does usually give birth to 2-10 kits in one litter. However, there might be one unlucky runt though.
I believe that would be the female. The hyena is a dog and female dogs give birth.
Bison cows primarily give birth to one calf a year.
A cheetah can give birth to as few as one cub and as many as nine cubs. Average litter size is three to five cubs.
humans
Without much more information the question can not be answered accurately. Crayfish are scavengers and guppies are not their natural prey. If the crayfish is small enough and your guppies don't have long flowing fins then the guppies may well be too fast for the crayfish to catch. So the answer then would be none. Are you feeding the crays dead guppies? If so I would add one and see how long it takes the crayfish to eat it. Then I would add more and more dead guppies one at a time as the crayfish devours them. As the crayfish grows so it will eat more.
a black one
One place is behind the church in Lumbridge. You need a crayfish cage to fish them.