There are many, many saltwater fish available in the pet trade, but not all are suitable for beginner hobbyists, and some are not suitable for any tank at all. Many people are tempted to choose which species to include in their saltwater tank based solely on the appearance of the fish, but this is a dangerous method. There are a great many saltwater fish that are breathtakingly beautiful but not appropriate or safe for life in captivity, particularly in the tank of a novice aquarist. The fish listed below are just a few examples.
There are quite a few species of venomous saltwater fish that are commonly offered for sale. Venomous species are fish that are able to inflict a painful toxic sting by means of sharp spines on their bodies. As is true of most animals, venomous fish can be some of the most beautiful species, but they should not be kept by beginners. One venomous fish that is commonly seen for sale is the lionfish. Although lionfish are generally not aggressive, their sting is quite painful. Several species of lionfish can do well under the care of an advanced hobbyist, but a few species of lionfish (one being the stonefish) are dangerous for all aquarists, regardless of their experience level. The venom of these fish can cause paralysis or death.
While not recommended for the beginner aquarist, butterflyfish are amazingly beautiful creatures. Some species can be kept by advanced hobbyists, but other species rarely do well in any captive environment, including the four-eyes butterflyfish, the ornate butterflyfish, and the chevron butterflyfish. These fish have very specific dietary requirements that are virtually impossible for the average aquarist to provide.
The Moorish idol is the only species in its genus and has a very unique appearance to match. It is black, white, and yellow with a distinctly pointed snout. Unfortunately, these beautiful fish are not recommended for captive aquariums, particularly those of novice hobbyists. Their natural environment is in the Pacific and Indian oceans, so they will take quite a long and stressful journey before arriving at your local fish store. This is thought to be a major part of the reason that they rarely survive for long in captivity.