Starfish are invertebrates that provide the home aquarium with a splash of colour and some textured visual variety. While they are somewhat delicate and require exacting standards in terms of water quality, they are typically easy to care for after their needs are met. However, because starfish are not very mobile animals, it can be difficult to tell whether a starfish is dead or alive. If the starfish is dead, it should be removed from the tank immediately to prevent contaminating the tank.
Observe the starfish. While they do not move a great deal, they do move when they are fed. If the starfish is moving, it is alive.
Put on a pair of waterproof gloves.
Scoop up your starfish gently without removing it from the water. Any sudden changes in its environment can stress the animal and cause it to shed limbs or begin to disintegrate. Suddenly being lifted into the air is shocking for starfish, as is rough or careless handing.
Feel for the tube feet underneath the starfish. Tube feet are the hundreds of short, hollow cylinder-like structures on the bottom of the starfish. If they retract against your fingers, the starfish is alive. If the feet are limp, the starfish is severely ill or dead.
Touch the starfish's body. A living, healthy starfish has a firm, almost rigid body. If the body is limp or yielding to the touch, the starfish might be dead or dying.
If you suspect that your starfish is dead, dying or ill, remove it from the tank immediately and isolate it. While it might get better, it can also spread infections to other members of the tank. If you see white spots on your starfish, take it to a veterinarian or to a pet shop with marine animal experience. It has an infection of some sort that needs treatment.