Green Swallowtail - Chromis viridis
When I first started in marine aquarium keeping and visited the first dealers, this fish, with its shimmering green-blue appearance, immediately caught my eye. Chromis viridis (Green Swallowtail ) are often sold here as schooling fish. This is also the case in the ocean, where you can find large schools migrating through the coral reefs. Unfortunately, things are a bit different in our aquariums.
Behavior and appearance
The very intense green/blue glow distinguishes the Chromi, and anyone entering the aquarium will immediately spot this aquarium inhabitant. These fish look best under LED light. They have an elongated oval shape and fins that resemble a swallowtail; hence the name "green swallowtail". With age, the males, which grow larger than the females, develop a stunning blue pattern that contrasts sharply with the rest of the coloration. Chromis reach a size of 5-8 cm. The Chromis viridis is generally readily available in stores and is also quite inexpensive.
Initially, the swallowtail will hide in the rocks or larger corals at the slightest movement in front of the tank. Over time, this behavior will decrease, but never completely disappear. These creatures, however, bring some movement into the aquarium. It's always interesting to observe how gracefully these fish try to get into even the smallest hiding place. Even backwards if necessary :)
food
Feeding is usually not a problem for this species. They will eat virtually anything offered. Frozen food species such as brine shrimp, mysis, and lobster eggs, as well as flakes and pellets, are readily accepted. Things get particularly lively in the tank when newly hatched brine shrimp nauplii are fed. But be careful, young chromis grow very quickly and become large when fed nauplii!
Chromis have recently developed a very efficient feeding mechanism, as scientists have recently discovered. With very little energy expenditure, this species can quickly consume small food items such as plankton.
In the pool
What a Chromi needs is a hiding place; caves and porous rocks are ideal. However, they prefer a large coral as a shelter.
Now we come to the statement that the Chromi is a schooling fish. This is basically true, but the fact is that many of us have tanks under 600 liters. I witnessed it myself how a group of 10 Chromis in my 65-liter cube gradually diminished in number. In the end, only a pair remained. In contrast, in the 400-liter room divider (150 x 50 x 50 cm), I observed that the fish get along very well. They have plenty of swimming space and also opportunities to avoid each other. They swim together as a group in this tank, and there is virtually no rivalry, except for the occasional chasing of conspecifics to show who is the boss. After more than 8 months, there have been no losses... they just keep getting bigger :o)
After I introduced eight shad into the tank, the chromis became calmer. The group now splits up more often and forms a community with the shad.
Swimming space is also very important for chromis. I wouldn't recommend more than 10 animals in a tank of less than 500 liters, unless the tank is longer. For a group of 6-8 animals, you should therefore have an aquarium of at least 350-400 liters, and an elongated tank is advantageous. This allows the swallowtails to easily avoid each other and avoid rivalry.
In society
Like all perch species, the chromi can be a bit of a bully, but this is quite limited. They generally never attack or chase other fish. I've only once witnessed a very large representative of this species chase a newly introduced dwarf emperor to defend its territory. But after a short time, even the chromi had to admit that the emperor was clearly the boss.
Tip for beginners
The Chromi is also a good fish for beginners, feeding very quickly and being robust. This fish is also well-suited for newly set up tanks. After about 1-2 weeks, I introduce a small group of 6-8 fish into the new tank, along with some corals. The Chromi is not as sensitive to slightly higher water parameters and stimulates the aquarium biology.
A fish that brings life to the saltwater aquarium and impresses with its color. However, the size of the tank and the number of animals must be taken into account.
Synonym: Chromis viridis - Cuvier, 1830