The Ruby Cardinal, Apogon crassiceps, also known as the Ruby Red Cardinal or the Little Red Cardinalfish, has a uniform and semi-transparent red color, with a narrow mid lateral stripe with some members having a dark pigment on the upper half. Their body is also a different shape than the traditional Cardinalfish, being long and slender rather than short and taller.
The Ruby Cardinal is a slower swimmer, and extremely peaceful in nature, and should be housed with other reef safe, and peaceful tank mates. Because of their timid nature, they are a great choice to house with Seahorses and Pipefish. They can grow to be about 2″ fully mature, and should be kept in a tank with plenty of live rock or plants to offer hiding places during the day. The Ruby Cardinal has a nocturnal living habit and will be most active during the night.
Since the Ruby Cardinal is very social, they do best in small groups or schools of odd numbers, as long as they are placed in an appropriate sized tank of no less than 30 gallons as a group, and can be kept in a tank of 10 gallons individually. Larger tanks could allow for larger schools, and like many other schooling fish, the Ruby Cardinal will form a strict hierarchy when kept in small groups within the aquarium. Although some species do use aggression to exert dominance, this member of the family Apogonidae does not. They are an excellent choice for beginner aquarists as they are active, friendly, easy to care for, and easily adapt to captive feeding.
Ruby Cardinals are carnivorous, and should be fed a diet of vitamin enriched Brine or Mysis shrimp, along with other finely chopped meaty preparations. They will also eat Copepods if present in the tank. If you are finding the Cardinalfish is having difficulties eating, it can be best to offer food at night. They will thrive in a temperature range of 72 – 75°F and a pH of 8.1-8.4.