A reef tank is a perfect environment for keeping more than one species of pygmy angelfish, because this type of aquarium is usually replete with hiding places (a must when trying to house multiple Centropyge species). But are these fish a threat to your invertebrates? Looking at their natural diets, it would seem as though they would pose no threat to sessile invertebrates. However, most of these angelfish do feed on detritus, and coral slime falls into this category. So, although they usually do not feed directly on coral polyps, they will graze on the slime they exude.
The coral species often used as a feeding substrate are the larger-polyped hard corals, like elegance (Catalaphyllia jardinei), open brain (Trachyphyllia geoffroyi), tooth (Lobophyllia spp.) and crater (Cynarina spp.), as well as zoanthids. The slime on tridacnid clam mantles is also a food source for pygmy angelfish. If you have one of these angels in an aquarium with corals or clams, and the invertebrate is constantly closed up, there is a good chance the angelfish is bothering it. Some pygmy angelfish will also nip at the oral disc of anemones, feeding on their feces, or will even eat dying corals or anemones. These angels will also pester feather duster and Christmas tree worms by nipping at their feathery feeding appendages.
As for their damaging sessile invertebrates, there seem to be patterns within the various pygmy species, but there is also a considerable degree of individual variation. For example, the cherubfish (C. argi) can typically be kept with most stony and soft corals without inflicting damage. However, an occasional specimen will begin picking at the tissue of elegance or open brain corals or the polyps of Xenia or Anthelia. On the other hand, although most lemonpeel angelfish will nip at corals and should not be placed in the reef aquarium, occasional specimens will not develop this bad habit.
The species that are less likely to cause damage to your invertebrates include the members of the argi complex: the African flameback (C. acanthops), Caribbean flameback (C. aurantonota), cherubfish and resplendent pygmy (C. resplendens). Other less-dangerous angelfish include Fisher's (C. fisheri), whitetailed (C. flavicauda) and multibarred. In my experience, the most risky species to add include the bicolor (C. bicolor), lemonpeel and keyhole (C. tibicen). The coral beauty (C. bispinosa), rusty (C. ferrugatus), Herald's, flame, halfblack, golden, multicolor, Colin's and purplemask fall somewhere in between the others in terms of sessile invertebrate compatibility.
No matter what species you are thinking of adding, remember that introducing any angelfish to your reef aquarium always entails some degree of risk. The corals least likely to be bothered by your pygmy angelfish are those that have some form of toxicity and are distasteful. These species, which are avoided by generalized predators, include some members (not all) of the following genera: Lemnalia, Sinularia, Sarcophyton, Cladiella, Paralemnalia and Effltounaria.
This article first appeared in the May 2004 issue of Aquarium Fish magazine.
Angelfish Care:
If you want to keep more than one pygmy angelfish in the same aquarium, you will have greater success if your aquarium is 70 gallons or more and is packed with hiding places.
They should not be exposed to the physical stresses of a newly established marine tank. The aquarium should be set up and running for three or four months before adding any species of angelfish. This ensures that the nitrogen cycle in the tank has been completed and the levels of ammonia and nitrite are so low as to be immeasurable.
Acclimating Angelfish is very important, as these fish have been known to go into shock.
Before purchasing a pygmy angelfish, examine the sides of the fish very carefully for raised scales or red areas.
