Thor amboinensis – Sexy Shrimp
Thor amboinensis was first described by Johannes Govertus de Man in 1888. The shrimp belong to the family Thoridae, which has recently been revised and recognized. The genus name Thor is derived from the Norse god of thunder, while the species name amboinensis refers to Ambon, an island in the Moluccas, Indonesia, where the species was originally found. Their common name is Sexy Shrimp as their “dance” is sexy.
Description
General description: Thor amboinensis is a small shrimp that grows to about two centimeters in length. The shrimp has an olive-brown color with symmetrically placed white spots, bordered with thin blue lines. The body is characteristically arched, with the caudal fin carried above the head.
Differences between sexes: Males and females of Thor amboinensis show no obvious physical differences, but males can change into females later in life, a process known as protandrous hermaphroditism. Behavioral differences between the sexes have not been specifically documented.
Behavior and temperament: Thor amboinensis is a peaceful shrimp that often lives in groups within the tentacles of sea anemones. They are social and are often kept in pairs or small groups in aquariums. They are not aggressive and display a characteristic behavior of bending their tail upwards and vibrating.
Life expectancy: In the wild, these shrimp can live for several years, while in a well-maintained aquarium, they can live up to two years.
Symbiosis with anemones: Thor amboinensis lives in symbiosis with several species of sea anemones, such as:
- Actinodendron arboreum
- Antheopsis papillosa
- Bartholomea annulata
- Condylactis gigantea
- Cryptodendrum adhaesivum
- Laviactis lucida
- Lebrunia danae
- Lebrunia neglecta
- Stichodactyla haddoni
- Stichodactyla helianthus
- Stichodactyla tapetum
- Telmatactis cricoides
Protandrous hermaphroditism is a fascinating phenomenon that occurs in the shrimp Thor amboinensis, also known as the sexy shrimp. This means that individuals of this species first mature as males and later in life change into females. Here is a detailed explanation of this process:
What is Protandrous Hermaphroditism?
Protandrous hermaphroditism is a form of sequential hermaphroditism in which an organism begins life as a male and changes to a female later in life. This process is often regulated by internal and external factors such as age, size, social structure, and environmental conditions.
How does it work with Thor amboinensis ?
In Thor amboinensis, each individual begins life as a male. As the shrimp grow older and larger, some males undergo a sex change and become females. This process is often observed in social groups where the largest and most dominant individuals become females.
Biological Mechanisms
The biological mechanisms behind protandrous hermaphroditism in Thor amboinensis include hormonal changes that affect the development of the reproductive organs. Males have gonopores on their fifth pereopods and produce sperm, while females have gonopores on their third pereopods and produce eggs.
Benefits of Protandrous Hermaphroditism
- Optimizing Reproductive Success: By maturing as males first, smaller individuals can reproduce without investing the energy and resources needed to produce eggs. As they grow larger and have more resources, they can change into females and produce eggs, which is more energy-intensive.
- Flexibility in Social Structures: In social groups, sex change can help maintain the balance between males and females, which is essential for successful reproduction. This ensures that there are always enough females to lay eggs, while males can continue to mate.
Observations in the Aquarium
In aquariums it is often observed that the largest and most dominant shrimp in a group become females. This can be influenced by food availability, tank size and social interactions between the shrimp.
Protandrous hermaphroditism in Thor amboinensis is an adaptive strategy that helps maximize reproductive success and optimize social structure within the group. This phenomenon makes these shrimps not only fascinating to study, but also an interesting addition to any reef aquarium.
Biotope
Geographic distribution: Thor amboinensis has a very wide distribution and is found in the Red Sea, Indian Ocean, Pacific Ocean, Caribbean Sea, Gulf of Mexico, Madeira and the Canary Islands.
Natural habitat: These shrimps live mainly in shallow coral reefs and lagoons, where they find protection among the tentacles of sea anemones. The bottom of their habitat usually consists of sand and coral rubble.
Natural enemies: Specific natural enemies have not been documented, but larger predatory fish and other marine predators likely pose a threat.
Diet
Diet in the wild: Thor amboinensis is carnivorous, feeding on plankton and other small crustaceans such as brine shrimp and mysids. They also eat the mucus of their host anemone and the plankton particles trapped within it.
Diet in the aquarium: In the aquarium, they can be fed small pieces of meaty food, such as brine shrimp and mysis shrimp. They are reef-safe and do not eat coral or polyps.
The Aquarium
Aquarium size: A nano aquarium of at least 20 liters is suitable for a pair of Thor amboinensis. For multiple pairs a larger aquarium of at least 40 liters is recommended.
Aquarium setup: The aquarium should be setup with coral and rocks to provide hiding places. A sandy bottom is best.
Water Parameters: Ideal water parameters are a calcium content of 380-430 ppm, a pH of 8.1-8.2, a specific gravity of 1.024-1.026, and a temperature of 22-27°C.
Introduction to the aquarium: It is best to introduce Thor amboinensis into a well-matured aquarium where algae and microorganisms are present.
Compatibility: Thor amboinensis can coexist with other peaceful reef dwellers such as clownfish, gobies, and small wrasses. Large predatory fish such as triggerfish, larger wrasses, coral climbers, and angelfish are unsuitable tankmates.
Breeding aquarium and conditioning
Breeding in a normal aquarium: Thor amboinensis can be bred in a normal aquarium, but a special breeding aquarium of about 40 liters with a constant temperature of 26.5°C and a salinity of 1025 is recommended.
Conditioning: The shrimp can be conditioned with a diet of artemia and mysis shrimp. It is not necessary to temporarily separate the males and females.
The spawn
Colors and courtship: During spawning, the colors of the shrimps become more intense. The courtship ritual involves vibrating the tail and mating usually takes place in the evening. The eggs are carried by the female under her abdomen until they hatch.
Raising the fry
Hatching: The eggs hatch after about 28 days. The larvae begin to swim freely shortly after hatching and there is no parental care after hatching. The first food for the young shrimp consists of artemia nauplii and other small planktonic organisms.
Particularities
Special features: Thor amboinensis is a protandrous hermaphrodite, meaning they mature as males and change into females later in life. They have a characteristic behavior of bending their tails upwards and vibrating, which has earned them the nickname “sexy shrimp.”
Conclusion
Thor amboinensis is a relatively easy shrimp to keep, suitable for both beginners and advanced aquarists. They are peaceful, social and can live well with other peaceful reef inhabitants. Their unique behavior and symbiotic relationship with anemones make them an interesting addition to any reef aquarium.
Video
Author
John de Lange
Copyright images
John de Lange