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Razorfish Wrasses

Bonus content from the April 2011 AFI magazine article The Dragon's Lair.

Rosy Razorfish ( Xyrichtys martinicensis . Via Gdiggers/Wikimedia

The subfamily Xyrichtyinae (formerly Hemipteronotinae) is a fascinating group of wrasses that can make fascinating aquarium inhabitants. Some genera in this subfamily include Ammolabrus, Cymolutes, Iniistius, Novaculoides and Xyrichtys. The razorfish tribe is represented in rocky and coral reef habitats around the world. Some species are wide-ranging (e.g., Iniistius pavo), while others have a very limited distribution. Several species have been described in recent years. For example, Xyrichtys koteamea is a species only known from Easter Island that was described in 2004. It is one of the most colorful members of the tribe, sporting a bright red coloration. Another attractive, newly described species is Halstead’s razorfish (X. halsteadi). This fish is a resident of Papua New Guinea, the Mariana Islands, Wake Island and the Society Islands.

The razorfishes are residents of sand flats, sand slopes and sea grass beds. They share these habitats with garden eels, sand divers and flatfishes. Razorfishes are well-known from their sand-diving and sand-swimming behavior. When they are threatened by predators and at night, when they are most vulnerable, they will dive, head first, into the sand. They can also “swim,” to some extent, under soft sand. Many a diver has watched a razorfish disappear at one spot, only to reemerge 3 feet or more away from its original entry point. The razorfishes have certain spots where they prefer to initiate their dives (referred to by some as their “dive sites”) and will typically hover above their “dive site” before plunging into the sand. At least some razorfishes prepare the sand at these locations beforehand so that they can dive into them more rapidly. For example, the finescaled razorfish (Cymolutes torquatus) will move rubble, bits of sea grass and twigs from a location in their territory where they typically dive when threatened. The green razorfish (X. splendens) will soften up the substrate in areas with coarse sand and rubble substrate by repeatedly diving into the sand in a specific location (these are known as “maintenance dives”). This loosens up the substrate and makes it easier for the fish to penetrate when danger threatens. It has been suggested that the mucus that the fish exudes also softens the sand in an area where it engages in maintenance dives.

To avoid predators, razorfishes do not always dive into the sand. Studies have shown that most species of razorfish are reluctant to dive in response to predators and usually only do so as a last resort (i.e., when the predator comes too near). When a razorfish buries itself, it can no longer keep track of the predator’s activities. When it reemerges from the sand, it may find itself in a more precarious situation than when it engaged in its sand dive! Indeed, some predators will remain in the area and wait. The length of time that a razorfish remains buried, after having responded to a predator, may be less than a minute to more than an hour.

This means that the razorfishkeeper needs an aquarium with a larger surface area with a bed of deep, fine sand. Re-creating a microhabitat where it can engage in this antipredation behavior is essential for these fish to acclimate to their aquarium homes. Once they get used to you, they will spend less time under the sand and more time showing off in full view.

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Article Categories:
Fish · Saltwater Fish