The Yellownose Butterfly
The Yellownose or Yellowsnout Butterfly (Chaetodon flavirostris) is also commonly called the Black Butterfly. They are members of the family Chaetodontidae, better known to us as the butterflyfishes. The longest fish on record is just shy of 8 inches long, but are unlikely to achieve this size. They are much more commonly seen in the five-to-six-inch range as full grown adults.
This fish displays two separate, and equally beautiful colorations. The juvenile coloration is lighter colors and a yellow margin, plus an eye spot on the dorsal fin, and a dark vertical bar through the eye. As an adult they are uniformly dark with orange / yellow fins and face. Adults also develop a dark spot on their nape (the area between the mouth and dorsal fin).
Yellownose Butterflies are found in the South Pacific from Australia to the Pitcairn islands. They prefer lagoon type habitats but can also be found on the reef. They are generally found in relatively shallow water over rubble and sand substrates in mixed lagoon habitats with coral and macroalgae growth.
Many Butterflyfish have reputations for being challenging to keep, as many of them have very specific diets, and Yellownose Butterflyfish have an undeserved reputation as they are not obligate corallivores (something that eats only coral). In the wild, Yellownose graze on algae and the correlated life on the rock of the reef. This includes many things that reef aquarists try to culture such as coral, sponges and other sessile (non-moving) invertebrates. While this makes them prohibitive to keep in reef aquaria, it generally means they are more open to trying a wide variety of foods, and thus easier to segue onto a prepared diet. As grazers they get a little bit of everything in their diet, and trying to mimic this is important. In house, we base their captive diet around high quality frozen foods and Nutramar shots as these offer a very balanced nutritional profile and the butterfly fish like to pick at them, mimicking a normal feeding activity for them. This fish consumes a lot of macroalgae in the wild and so we also supplement their diet with a variety of Nutramar algae. For a hobbyist with a very picky eater, they can generally be induced to captive feeding with irresistible foods like Gamma Cockle in Shell, Nutramar Ova etc.
Being an active fish that spends its days grazing on rock, the larger and more established your aquarium is, the better. When thinking about décor for Yellownose Butterfly fish, an emphasis should be placed on current and open space for them to swim and get exercise in and as such, we suggest displays of 100+ gallons and five (or more) feet in length for happy and healthy fish at grow out. The natural environment of this fish would be coral heavy, or have isolated patches of coral and macroalgae. They come from relatively shallow water generally and so the bright lighting that we are accustomed to in reef aquaria shouldn’t bother these fish. Having a tank that has been seeded with live rock to encourage different types of algae, sponges, and other growth on the rocks will give these fish opportunities to graze would also help these fish thrive. They are not overly picky about temperature, low 70s to 80, though as with all aquarium fish, stability of whatever temperature you settle on is important.
As of the writing of this article, the Yellownose Butterfly has not yet been bred in the aquarium. It is known that these fish will form pairs as they mature. They can be housed in pairs in the aquarium, with some risk of aggression. If the pairs do not cohabitate well, one will need to be removed; they will not “work it out”. They are generally very peaceful with other non-butterfly fish and should only be kept in aquariums with mostly peaceful fish.
Yellownose Butterflies are beautiful fish with a unique set of care requirements and an inclination toward picking at and eating algae, clams, tubeworms, and a wide variety of corals in the home aquarium. However, they can do well in seasoned tanks that aren't housing these types of animals. If you have a very large, established aquarium, purchasing a sustainably harvested individual from Quality Marine is the right choice for you.