Wrasses are very beautiful and a real fun addition to a marine aquarium. They are usually very hardy and peaceful, however there are exceptions to every rule. A few species are extremely difficult to sustain in captivity, such as those in the genera Labroides. Some wrasse fish are social their entire lives, others are social as juveniles and become aggressive as adults, and yet others are aggressive their entire lives. Then there are species that are territorial just with members of their own kind.