also known as the Scarlet Cardinalfish, is a popular fish among hobbyists due to its striking red coloration and active behavior. This fish belongs to the family Apogonidae, which is comprised of small, colorful fish that are found in both shallow and deep waters in tropical and subtropical regions around the world.

The Ruby Cardinalfish typically grows to a maximum length of 3 inches (7.6 cm) and has a slender, elongated body shape. The body is predominantly red in color, with some individuals exhibiting a slight gradient towards pink or orange on the belly. The fins are transparent and may have a slight red tint. The eyes are large and black, and the mouth is relatively small.

In terms of behavior, the Ruby Cardinalfish is a peaceful and sociable fish that can be kept in groups of 5 or more individuals in a properly sized aquarium. They are not aggressive towards other fish, but may be territorial towards conspecifics. This fish is generally active during the day and tends to occupy the middle to lower levels of the aquarium. It is important to provide ample hiding places in the aquarium, such as live rock or coral, as well as plenty of open swimming space.

The Ruby Cardinalfish is generally easy to care for and can be fed a variety of commercially available fish foods, including pellets, flakes, and frozen foods. They should be fed small meals multiple times a day, as they have a relatively small stomach capacity. This fish is also known to be a relatively hardy species that can tolerate a range of water parameters, although they prefer a temperature range of 72-80°F (22-27°C) and a pH of 8.1-8.4.

Overall, the Ruby Cardinalfish is a beautiful and peaceful addition to a reef or community aquarium. Its striking red coloration and active behavior make it a popular choice among both beginner and experienced hobbyists alike.