The Thalassoma lucasanum is commonly known as Mexican Rock Wrasse, Mexican Rainbow Wrasse and Cortez Rainbow Wrasse. The Mexican Rainbow/Rock Wrasse fish has an amazing cigar shaped body. These fish are known to undergo a change in the body colour as they grow. A juvenile Mexican Rainbow/Rock Wrasse fish are greenish in colour with yellow underside and jet black dorsal. Caudal fins have a reddish coloured patch which diffuses into the rest of the body. As they mature this bright yellow gives way to orange-brown. In an adult Mexican Rainbow/Rock Wrasse fish, it is observed that green colour is bound to appear again. Male fish has a dark blue band behind the pectoral fins which is usually mistaken to be black in colour .In the terminal phase the Mexican Rainbow/Rock Wrasse fish appears blue .But, there is a yellow saddle-like marking just behind head and the head is scale less. The Mexican Rainbow/Rock Wrasse fish has sharp pointed teeth that protrude from the mouth.
The Mexican Rainbow/Rock Wrasse fish are noted not only for changing the colour but also, 5% of them are known to change their gender. This hermaphrodite behavior is demonstrated as they mature. Sexual maturity is attained at the age of two. The spawning takes place mainly during peak summer. The Mexican Rainbow/Rock Wrasse fish prefer to stay in shallow water. It is diurnal and sleeps with its head buried in sand or algae, only exposing their heads. This process is also done to protect themselves from the enemies.
The Mexican Rainbow/Rock Wrasse fish have a good life span when compared to other fish and hence it is a more popular aquarium fish. They need not only open water, but also live rocks to hide from its rivals. This is a moderately hardy medium maintenance fish. Though the Mexican Rainbow/Rock Wrasse is a community fish, at times they are aggressive towards the tank mates. It is ideal to have two or three Mexican Rainbow/Rock Wrasse fish in the same tank.
Maximum Size: The Mexican Rainbow/Rock Wrasse fish can have a maximum length of 4 inches.
General Size Specifications: The smaller size Mexican Rainbow/Rock Wrasse is observed generally to be 1 to 2 inches, the medium ones about 3 to 4 inches and the larger variety 5 to 6 inches.
Minimum Tank Size: An ideal tank for this fish should be at least 80 gallons, with lots of space and water to swim. Quality of water has to be properly maintained (SG 1.020 - 1.025, pH 8.1 - 8.4, Temp. 72 - 78° F).
Habitat: Range: The Mexican Rainbow/Rock Wrasse fish is very commonly found in Central America, Central Gulf of California to Central Peru and almost all the offshore islands except Clipperton
Feeding and Diet: Being a carnivorous fish, Mexican Rainbow/Rock Wrasse prefers to feed on meaty foods such as live feeder, small fish, grass shrimp, benthic crustaceans, and fish eggs. They are also known to clean parasites from other fish.