Clownfish grow to about 4 inches (10 cm) and live in families next to a host anemone (Saltwater invertebrates of the phylum Cnidaria. They have stinging nematocysts which kill their prey. They often have a symbiotic relationship with anemonefish). In fact they typically sleep nested near the mouth, or oral disk of the anemone.
Most clownfish start out as males. Later, if the dominant female dies, a male will become a female.
Clownfish typically lay hundreds of eggs on a flat rock near their host anemone. The eggs are tiny capsules that have a filament that attaches tightly to the rock. The males fan the eggs and clean the area around the eggs in order to keep fungus from growing. Then, at night, after about 7 days, the eggs hatch often timed to the phases of the moon.
Nutrition - Clownfish eat plankton made up of tiny crustaceans called copepods, larval tunicates and algae.
Longevity - They live up to 10 years in the wild and have been recorded to live more than 18 years in captivity.
Symbiosis is what makes it all possible. Obligate symbiosis (A type of symbiosis where one partner must live with another in order to survive) works like this. The anemone's stings keep predators away. At the same time, the clownfish attracts food to the anemone, so it's a great arrangement. Clownfish also drive away Butterflyfish which eat anemones.
Clark's Anemonefish in Manado, Sulawesi, Indonesia