Marine

I don't know much about marine fish, but they are a large group of aquarium species, and fish in general, so I will include a page showcasing some common aquarium species and some of the more beautiful specimens that aren't common to home aquaria.

Volitans Lionfish (Pterois volitans)
This fish is a very popular, but large, marine aquarium fish. They are carnivorous and will take anything from shrimp and krill to small fish. Their dorsal fin rays contain spines carrying poison that can kill a person.

Percula Clownfish (Amphiprion percula)
Clownfish are a hardy and popular group that is often well represented in fish stores. They are typically small and do well in reef tanks where they will set up a symbiotic relationship with certain marine anemones- the fish gains protection from bigger fish (anemone have poisonous "stinging" tentacles that do not seem to have any affect on the Clownfish, but will kill other fish) and the clowns keep the anemone clean from particles that could damage it.

White-jawed Moray Eel (Gymnothorax moringa)
Another popular large fish. These fish are not terribly active, sometimes seen slithering about the tank. They lack most body fins and have a very small tail fin. They eat small fish and inverts that happen past their caves and hideouts.

Three-Stripe Damselfish (Dascyllus aruanus)
A small inexpensive fish with a bad temper, typically used to cycle tanks because they are so hardy. Most species are very aggressive fin nippers. Damselfish species come in many colors, and are fairly popular despite their aggressive tendencies.

Blue Tang (Paracantharus hepatus)
A highly sought after and very beautiful fish. Tend to be difficult to acclimate to home aquaria, and do get rather large. This species has been called the "bluest thing on earth." Keeping a single individual in a tank doesn't do this animal justice- one truly cannot appreciate their beauty until you've seen an entire school moving together as one.