Thalassoma lutescens – Yellow-Brown Wrasse
Thalassoma lutescens was first described by Lay & Bennett in 1839. They belong to the family Labridae, also known as wrasses. The genus name Thalassoma is derived from the Greek ‘thalassa’ (sea) and ‘soma’ (body), referring to the color of the sea. The species name lutescens means ‘yellowish’ in Latin, referring to the yellow color of the fish.
Synonyms:
- Julis lutescens (Lay & Bennett, 1839)
Description
General description:
Thalassoma lutescens has an elongated and slender body. The head and flank are yellowish with green and blue hues. The fins are often yellow with blue edges. Adult males can grow up to 30 centimeters long.
Differences between males and females:
- Males: Larger and more colorful, with a green to blue color and red stripes on the head and body.
- Females: Less colorful, often yellow with a black stripe from the eye to the base of the tail.
- Juveniles: Greenish above with a black stripe and white below.
Behavior and Temperament:
Thalassoma lutescens is an active and territorial fish. They are semi-aggressive and can be aggressive towards smaller fish and invertebrates. They live solitary or in small groups and are often found in the middle waters of the aquarium.
Life expectancy:
In the wild they can live for several years, but in a well-maintained aquarium, they can live up to 10 years.
Sex change
Thalassoma lutescens, undergoes a fascinating sex change during its life. This species of fish is a proterogynous hermaphroditic, meaning that all individuals start out as female and change sex to male later in life.
Sex change
Female phase:
- Colors: In the female phase the fish are generally less colorful. The juveniles have a greenish color on the upper side with a black stripe running from behind the eye to the base of the tail. The underside of the body is white with a yellow stripe from the chin to the lower part of the base of the tail.
- Behavior: Females are often less territorial and aggressive than males. They usually live in groups and show less conspicuous behavior.
Transition phase:
- Colors: During the transition from female to male, the fish’s colors begin to change. The head and body gain broader, wavy lines in reddish tones, and the rest of the body abruptly turns greenish to bluish.
- Behavior: At this stage the fish may begin to show more territorial behavior and begin to take on the role of a male within the group.
Male phase:
- Colors: Adult males are much more colorful and striking than females. They have a green to blue color with red stripes on the head and body. The head is often yellow or pinkish-reddish with blue stripes. The fins are also colorful: the dorsal and anal fins are red with a green edge, while the caudal and pectoral fins are yellow with a blue edge.
- Behavior: Males are very territorial and aggressive, especially towards other males and smaller fish. They often display courtship behavior and defend their territory fiercely.
Color changes per phase
- Juveniles: Greenish above with a black stripe and white below. Fins are transparent.
- Females: Yellowish with a black stripe from the eye to the base of the tail.
- Transitional phase: The body acquires broader, wavy lines in reddish tones, and the rest of the body becomes greenish to bluish.
- Males: Green to blue color with red stripes on head and body. Head is yellow or pinkish-reddish with blue stripes. Fins are colorful: dorsal and anal fins are red with a green edge, while caudal and pectoral fins are yellow with a blue edge.
This sex change and the associated color changes make Thalassoma lutescens a particularly interesting and attractive fish species for aquarists.
Cocoon
Thalassoma lutescens exhibits a fascinating behavior where they burrow into the sand and form a cocoon. This behavior is mainly a defense mechanism and has several functions. Let’s take a closer look at the cocoon and how it protects against attacks from larger fish.
What does the cocoon consist of?
The cocoon that Thalassoma lutescens forms consists of a slimy substance that is secreted by the fish. This layer of slime completely envelops the fish when it burrows into the sand. The cocoon is a thin but effective barrier that protects the fish from various threats.
Protection against attacks from larger fish
- Camouflage:
- The cocoon helps camouflage the fish in the sand. By completely covering the fish, it becomes more difficult for predators to detect the fish. The cocoon often takes on the color and texture of the surrounding sand, making the fish virtually invisible to predators.
- Physical barrier:
- The mucus layer forms a physical barrier that protects the fish from direct attack. Although the cocoon is not completely impenetrable, it does provide an extra layer of protection that makes it more difficult for predators to reach the fish.
- Chemical defense:
- The slime layer may also contain chemicals that deter predators. These chemicals can be unpleasant to predators, making them less likely to attack the fish.
- Protection against parasites:
- In addition to protection from predators, the cocoon also offers protection from parasites. The mucus layer prevents parasites from attaching to the fish, which contributes to the overall health of the fish.
Depth of the sand layer
For Thalassoma lutescens it is important that the sand layer in the aquarium is deep enough to be able to dig in. A sand layer of at least 5 to 7 cm is recommended. This provides enough depth for the fish to dig in completely and form a cocoon.
Summary
The cocoon that Thalassoma lutescens forms consists of a slimy substance that protects the fish by camouflage, a physical barrier, chemical defense and protection against parasites. A sand layer of at least 5 to 7 cm in the aquarium is essential to allow this natural behavior.
Biotope
Natural habitat:
Thalassoma lutescens is found in coral reefs of the Indian and Pacific Oceans, including the coasts of Sri Lanka, Japan, South Australia and New Zealand. They live in areas with sandy bottoms up to a depth of 30 meters.
Habitat description:
They live among coral reefs and rocky areas, where there are many hiding places and food sources. The bottom consists mainly of sand and rocks.
Natural predators:
They have few natural predators due to their size and speed, but they are hunters themselves, feeding on small invertebrates.
Diet
Diet in the wild:
Thalassoma lutescens feeds primarily on small benthic invertebrates such as crabs, shrimp, snails, sea urchins and fish eggs.
Aquarium Diet:
In the aquarium they should be fed a varied diet of meaty foods such as enriched brine shrimp, mysis, and other marine-based frozen foods. They can also accept flakes and pellets.
Reef Safe:
They are reef-safe with caution, as they may eat small invertebrates such as shrimp and snails.
The Aquarium
Aquarium Size:
A minimum of 1000 liters is recommended for a single fish, with a larger aquarium required if you plan to keep multiple specimens.
Aquarium setup:
The aquarium should be setup with lots of live rock and coral to provide hiding places. A sandy bottom is ideal because they like to burrow. Depending on the size of the fish, a sand layer of at least 5 to 7 centimeters is needed.
Water parameters:
The best water parameters are a temperature of 24-28°C, a pH of 8.0-8.5, and a specific gravity of 1.020-1.026.
Aquarium Introduction:
It is best to introduce this species into a well-matured aquarium with sufficient algae and microfauna.
Compatibility:
They can live well with larger, semi-aggressive fish such as other large wrasses, surgeonfish, and angelfish. Avoid small, peaceful fish and invertebrates.
Breeding in the Aquarium
Breeding in an aquarium:
There are no specific reports of successful breeding in a common aquarium.
Particularities
Details:
Thalassoma lutescens is a proterogynous hermaphrodite, meaning they start out as females and change sex to males later in life. They are also known for their ability to jump out of open tanks, so a lid or net is essential.
Conclusion
Thalassoma lutescens is a beautiful and active fish suitable for advanced aquarists. They require a large aquarium and a varied diet. Although they can be reef safe, they should be kept with caution due to their tendency to eat small invertebrates. Their hermaphroditic nature and territorial behavior make them fascinating to observe, but also challenging to keep.
Video
Author
John de Lange
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