The family Colubrariidae is known from about eight species in the Marshalls. At least six of these (and maybe all Colubrarids) make their living as parasites, sucking the blood of sleeping fish. We first came across this in 1988, when one of us noticed on a seaward reef night dive that several specimens of Colubraria tortuosa, a species we did not see all that often, happened to be next to a couple of different large sleeping parrotfish, a fish that sleeps on the reef, often in small caves or ledges. Coincidence? In the past, we had tended to steer clear of sleeping parrots. If disturbed, they can blast out like a missile, potentially causing damage to an unwary diver. But this was worth a closer look. Indeed, over the next few years, we found six species of Colubraria highly associated with sleeping fish at night, usually parrots but sometimes other species as well, including tangs (Acanthurus pyroferus, Naso lituratus), groupers (Cephalopholis argus), triggers (Balistoides viridescens), and scorpions (Scorpaenopsis diabolus). Close observation revealed that all of the parasitic Colubraria have a very elongate proboscis that stretches out to the sleeping fish, finds a soft spot, apparently cuts into the flesh and sucks out fish blood. Real-life vampires! Usually the target of the proboscis is a soft spot: inside the mouth, gills, eye, or anal opening. Sometimes we have seen the proboscis simply slipped under a scale on the side of the fish's body. But it does not happen only at night. Apparently the Colubrariids can feed anytime, as long as they have an inactive fish. During the day we have seen Colubrariids actively sucking blood from a sleeping Priacanthus sp and on two different occasions, from immobile stonefish, Synanceia verrucosa. They may also parasitize shark species that rest on the bottom; we once found four Colubraria muricata together on top of the sand in a spot just vacated by a nurse shark (Nebrius ferrugineus). More detailed information on Colubrariid parasitism of sleeping fish can be found in Johnson, et al, 1995. Unfortunately, most of the photos we have of Colubrariids feeding are not all that good. The combination of shooting at night, getting the camera into position in the ledges and small caves where this is taking place, and the relative sensitivity of both the mollusks and the host fish to the photographer's lights and strobe, all make getting decent shots a somewhat dicey operation.
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