feed it turtle food but make sure the food is big.feed it lettuce and krill.also earthworms and fresh fish.
About 6 months
if the red eared slider's shell is 15cm. it is 5 years old!
Red Eared sliders are aggressive over food, territory mates, etc. Most likely it was due to that aggression. I would suggest separating the sliders and taking the injured slider a vet. Good Luck!
"Unfortunately, you can not tell the age of a turtle by it's size. Turtles grow depending on how big their environment is." Actually, no. A red eared slider does NOT grow to their environment. If you feed it, it will grow. If not it will, obviously not grow then die. But there is no way to tell how old a RES is unless you hatched it or know who hatched it. It does not matter how big it is. Some owners over feed or under feed their turtles so there is no way determining it by size either.
let them hear it as it drops in to the cage.
Its really a gamble to put any fish with a red eared slider , it depends how big the sucker fish is if it is small the turtle with probably eat it , you are supposed to let them grow up together i have a sucker fish with my red eared slider but they are baby's so they have not bothered it.
It dose not matter what age they have to be to eat earth worms
our red slider turtle is 1 1/2 years old and she will eat 5 small goldfish at a time.
Same as any other animal, either old age or some kind of disease.
of course! i have a baby red eared slider living with a big 8 inch turtle and they get along! you have to make sure they know and like each other before you put them both in the same tank
At one year.
It probably isn't normal, and it does not sound normal I would probably think about consulting a vet.