The following is a guest contribution from Joe Oliver, a resident Marine Biologist for the Curacao Sea Aquarium and Substation Curacao.
The Banks Butterflyfish (Prognathodes aya) and its relative the French or Three-Banded Butterflyfish (Prognathodes guyanensis), are both striking deepwater butterflyfish that are rarely seen in the aquarium trade. Even with quite large distribution ranges from the eastern US seaboard to Brazil for P. aya, and from Southern Florida to Northern Brazil for the P. guyanensis, these fishes are rarely collected due to the depths in which they live and technical detail needed to decompress them properly.
Despite the rarity and price of $500 for P. aya and $1,500 for P. guyanensis, these fishes make excellent aquarium inhabitants because of their hardiness and willingness to accept common aquarium foods like mysis, krill, and shrimp along with some pellet foods (this takes some training). Below we will go over some of the high points of each species, their habitat in the wild, some behaviors, and their captive husbandry.
Prognathodes aya received a very appropriate common name due to their tendency to be found on deep ledges, wrecks, and banks. Interestingly enough the P. aya was discovered in 1880 when a red snapper (then classified as Lutjanus aya) regurgitated the first specimen to be seen by scientists who consequently named it after the snapper responsible for the find. P. aya ranges as far north as North Carolina, can be found throughout the Caribbean, and even along the northern coast of South America. Even with this extensive range they are considered to be uncommon and because of the depths where they are normally found (50-200m), they are even rarer to encounter.
Their difficulty to acquire is made up for by their stunning beauty and their readiness to adapt to aquarium life. Unlike many other species of butterflyfishes in the aquarium trade P. aya is a hardy fish and readily adapts to the mixed variety of diets provided in the home aquarium. In the wild they are generalist browsers, spending much of their time moving along the reef in search of small crustaceans, worms, sessile invertebrates, and other organisms found on these deeper bank habitats.
Although their pattern is quite striking to our eyes, at the depths these fishes live, their pattern helps to break up their outline and hide their eyes while they move through the gorgonians, crinoids, and sponges that make up their habitat. In the wild they tolerate a wider range of temperatures than the average reef fish, and can be found in temperatures as low as 20C.
However, they are able to adapt to the warmer water and brighter light of a shallow water aquarium system, making them ideal aquarium candidates. One should use caution when considering a P. aya for a reef system due to their tendency to nip large/fleshy polyps and some gorgonians.
The French or Three-Banded Butterflyfish is a gorgeous fish that sometime finds its way into the aquarium trade despite the extreme depths and difficulties associated with collection. Prognathodes guyanensis is somewhat less common than P. aya, although its range is quite extensive throughout the Caribbean due to the depths and distance from shore normally needed to find their habitat.
Butterfly fishes are built for speed and maneuverability and the P. guyanensis is no slouch by any comparison. From personal experience this is one of the most difficult fishes I have ever participated in collecting. Even with a specially designed submarine it can take up to an hour to successfully catch a single specimen, I have the utmost respect for anyone that collects these fishes by mixed-gas or re-breathers, it’s amazing they were ever collected alive before the advent of remote marine technologies. This is because the P. guyanensis is quite a tough fish when it comes to its susceptibility to anesthetics, coupled with the ability to traverse 50m vertically in a single run.
It means these fishes can take several pulses of anesthetics, keep on trucking, run from 600 feet up to 450 feet, and back down again without breaking a sweat, which makes them quite a challenge to successfully collect. Even though these fishes are able to make large vertical migrations they must still be decompressed like any other deep water fish with a swim/gas bladder.
Their choice in habitat does not help much either. These fishes tend to inhabit walls and ledges at depths from 100m to 300m. Their diet is that of a generic omnivore consisting of a wide array of guyanensis worms, small crustaceans, mollusks, mysids, and possibly some gorgonian polyps. These deep reefs extend from 100m to 300m on the island of Curacao and run even deeper in other parts of the Caribbean.
Because the bulk of this habitat is below the photic zone there is not enough light energy to fuel photosynthesis like there is in shallow waters. These habitats are more reliant on currents and the transport of materials, along with marine snow and particulates that rain down from the surface. These habitats are dominated by stony sponges, which can be 1000s of years old, gorgonians, black corals, and a myriad of non-photosynthetic corals. This combination of filter feeding organisms provides refuge and food sources that are the core of this deeper food web. P. guyanensis are constantly searching these habitats in search of small prey or sessile invertebrates to browse.
P. guyanensis typically lives at depths below the permanent surface thermocline in the tropics and resides in waters with an average temperature between 20 and 26C. These fishes can tolerate warmer waters associated with reef systems but are in their element in cooler water. These fishes are stunning aquarium specimens and adapt to captivity quite readily once decompressed.
At the Curacao Sea Aquarium we have found they will take a wide variety of foods when offered including: Mysis (live and dead), krill, cut clams, cut fish, roe, and even some pellet foods. The white margined black bands on the yellow background give this fish a striking appearance along with the patch of horizontal yellow stripes seen in mature adults. The P. guyanensis has three distinct bands vs. the two of P. aya. On P. guyanensis all three bands extend onto the dorsal fin adding to its unique appearance.
These fishes are quite hardy but may be prone to bullying by larger or more aggressive species but on the other hand do not take much time to feed with confidence. These fishes may nip at large/fleshy polyps or gorgonians but are not specific feeders on any types of coral. Still one should use caution if considering this fish for a primarily coral dominated system.