News / Species Spotlight / They Came From The Deep: Mesophotic Aquarium Fishes (01/10/18)

They Came From The Deep: Mesophotic Aquarium Fishes

They Came From The Deep: Mesophotic Aquarium Fishes
The fishes available to marine aquarists can come from a variety of ecosystems. Many of the most affordable options originate from shallow lagoons and reef flats, while others come from the outer reef slopes, where the water is clearer and the currents stronger. Still others might be sourced from muddy or silty flats, far removed from the coral-rich biomes we might expect. But today well be focusing on those fishes that swim exclusively at great depths (relatively speaking the ocean is a pretty deep place).

Life in the ocean is often dictated by a combination of depth, illumination and temperature. Below 100 feet, the amount and composition of available light diminishes significantly, limiting the sorts of photosynthetic life that can survive. This has given rise to the term Mesophotic Coral Ecosystem, which references the reduced sunlight reaching the bottom. In association with this, there is often a sharp drop in temperatures, known as a thermocline.

Many if not most, of the corals found at these depths are unique to these habitats, especially as one travels further down. 500 feet is about where the light required for photosynthetic corals and algae to survive becomes inadequate, making this a sort of informal barrier for other types of organisms. As an example, the Acropora species found here are very obviously different from those found nearer the surface. Compare the delicate brown colonies of A. tenella to the robust and colorful A. monticulosa, and it becomes clear how these organisms are adapted for vastly different conditions of light and water flow.

This also holds true for fishes. Many of the species most beloved by aquarists come from mesophotic depths, but, as you might imagine, collecting them takes far more time and skill and equipment than what goes into plucking some damselfish out of knee-deep waters. For the deepest dives, bottomtime can be as little as 15 minutes, followed by hours of decompression for both the fish and the divers so that both can arrive safely to the surface. And this is why a deepwater wrasse can end up costing ten times more than its shallower counterparts.

So lets take a moment to highlight a few of these species that come to us from the briny deep

Magma Fairy Wrasse (Cirrhilabrus shutmani)
Cirrhilabrus is a vast genus, likely the largest in the entire wrasse family, with some subgroups in shallow waters (C. cyanopleura, C. lubbocki) and others that only swim at great depth (C. johnsoni, C. pylei). Its these deeper members that make this genus such a quintessential component of the mesophotic realm, often as one of the dominant zooplanktivores. The Magma Fairy Wrasse is an interesting example, as it was entirely unknown up until 2016, illustrating how little we know about the fishes that occur below traditional SCUBA depths. Specimens were discovered by aquarium collectors along the slopes of an undersea volcano in the northernmost islands of the Philippines. To date, they have only ever been encountered below 50 meters, and its likely to occur far deeper still. Its bright red coloration and short pelvic fins place it as a close relative of another deepwater fairy wrasse, Hawaiis very own Cirrhilabrus jordani. Of course, with collection now restricted from the Aloha State, aquarists will have to make do with C. shutmani.

Ventralis Anthias (Pseudanthias ventralis)
All across the Indo-Pacific, a characteristic component of deep reefs are small, colorful anthias in the genus Pseudanthias. This group is highly diverse, and, much like with fairy wrasses, some lineages occur in the shallows (P. squamipinnis) while most others become dominant further down (P. randalli, P. aurora). In the Central Pacific, the Ventralis Anthias is an especially noteworthy example. Aquarium specimens are most often sourced from the Coral Sea and other nearby islands, but it can also on occasion be had from the Cook Islands or French Polynesia. And, interestingly enough, these two fishes look completely different. In all likelihood, there is not one Ventralis Anthias, but several, each found in its own distinct corner of the sea. This is a common phenomenon for mesophotic life.



Royal Gramma (Gramma loreto)
You might be surprised to learn that some of the most familiar and cheaply available of aquarium fishes can also dwell in the deep. In the West Atlantic, the colorful little basslets in the genus Gramma are a prime example. The ubiquitous Royal Gramma (G. loreto) can be collected from caves and crevices as shallowly as 10-15 meters, but you can also find it as far down as 70 meters! Its cousin, the Blackcap Basslet (G. melacara) likes it deeper still, becoming increasingly abundant as one enters into the mesophotic realm, with reports from as far down as 135 meters! The same holds true for the ugly duckling of this group, the Yellowcheek Basslet (G. linki), which goes to show that not every deepwater species is especially colorful.





Mitratus Butterflyfish (Chaetodon mitratus)
Many butterflyfishes are specialists in mesophotic reefs. One of the deepest members of the family, Prognathodes guyotensis was recently rediscovered in the Mariana Islands at 270 meters, and its been collected elsewhere from nearly 1000 feet down, putting it in the barren zone beneath the mesophotic. A bit further up youll find an altogether different group that has carved out a place in this ecological niche, the handful of species in the subgenus Roaops. These occurs all across the Indo-Pacific, and, on account of their tendency to ignore most corals, these are some of the most desirable chaetodontids in the aquarium world. In the Pacific, Tinkers Butterflyfish (C. tinkeri) has established itself as arguably the most sought after species in the genus, owing to its stunning colors and hearty nature. Though, as with Cirrhilabrus jordani, it is no longer available. A bit to the south, it is replaced by the similar C. declivis, while to the west, C. burgessi takes over. But the most distinctive and colorful of the group is the Indian Ocean representative, C. mitratus. Its bright yellow coloration and bold black markings make this an iconic deepwater fish.

Multicolor Angelfish (Centropyge multicolor)
There are a multitude of angelfishes we could have chosen for this discussion. The Narcosis Angelfish (Centropyge narcosis) is perhaps most emblematic, though it is almost never available to aquarists. Its name derives from the dangerous condition known as nitrogen narcosis, AKA the bends, which divers (and fish) can develop is they return to the surface to quickly. This happened when the first specimens of this fish were collected, and its discoverers chose to name the fish in honor of this. A more obtainable choice is the Multicolor Angelfish (Centropyge multicolor), which occurs all over the Central Pacific below about 30 meters. Its unusual mix of colors and patterns have long made this fish a favorite. White fish are not a common sight on coral reefs, but several seem to dwell in the deep. Along with this fish, there is the Personatus Angelfish (Genicanthus personatus) and some of its relatives, as well as the inimitable Bandit Angelfish (Apolemichthys arcuatus).