Rabbits in My Aquariums
by Bob Goemans
First printed in TFH, May 2006
Rabbitfish belong in the “Order Perciformes” and “Suborder Acanthuroidei” as members of the “Family Siganidae,” which consists of 1 genus with about 27 described species. I should note that previously there was one genus with two subgenera, Lo and Siganus. However, there is insufficient evidence to continue to support the subgenus Lo in the opinion of some notable marine scientists. Those previously placed in the Lo subgenus are now considered to be in the Siganus genus.
These are laterally compressed fish and have small mouths similar to Surgeonfish, which they are actually related to. Their body sides produce little body slime, therefore they have a ‘dry’ feel when touched. And even though they produce little body slime, they are quite disease resistant and seem to withstand various skin parasites such as Cryptocaryon or Amyloodinium. And even though related to Surgeonfish, they do not have a similar tail spine, however all do have other venomous spines. A sting from these spines can result in a very painful experience. If stung, the wound should be immersed in hot water, which will greatly reduce the level of pain. Always be very careful when working with members of this fish family.
Rabbitfish are mostly found in the Indo-Pacific Ocean, yet a couple of species have migrated from the Red Sea through the Suez Canal to the Mediterranean Sea. Most live on the reef, with some preferring grassbeds and mangrove areas. In fact, those preferring reef locations have a more colorful appearance. Many of those found in mangrove and estuary areas have a more drab coloration.
In the wild they feed upon various forms/species of algae (macro and micro) including coralline, along with sponges, worms, sessile colonial tunicates and other small invertebrate. Even though technically considered an omnivore, they are excellent herbivores and require a large amount of vegetable matter in their diet. In fact, they are one of the better hair alga consumers and that’s a real plus in many of today’s aquariums. And even though their closed system diet should mostly consist of vegetable matter, especially some Spirulina flake and nori (dried seaweed/kelp), some meaty foodstuffs should also be made available. And if the aquarium is somewhat devoid of green growths, these fish should receive at least several feedings per day as they are grazing type animals.
Another plus is that they are quite disease resistant and very tolerant of poor water quality conditions. It should also be noted that every once and while rabbitfish will shed their outer skin, similar to what some leather corals do occasionally. And even though they are safe with most corals, I have found some to have a desire to pick on Xenia.
Keep in mind that adult members of this family are aggressive to each other, therefore only one per aquarium should be tried unless it’s a mated pair or a ‘very’ large aquarium. Unfortunately, the difference between male and female is not clear cut, as the female of each species tends to only be slightly larger than the male, making a positive identification nearly impossible. Yet, if two appear to be getting along with each other in a mixed fish environment, than there’s the possibility they may be a pair. Yet if two are purchased and moved to a small system, it might prove to be a mistake. Either way, more than one in the same aquarium is a gamble. And if they do pick on each other, they will become stressed, which will lead to opening the window for a possible disease to become started. And if so, other fish in the aquarium may also be affected.
There’s only a small percentage of the known species available in the trade. The most common are the Foxface Rabbitfish S. vulpinus; Magnificent Rabbitfish S. magnifica; One-spot Rabbitfish S. unimaculatus; and, the Blue-spotted Rabbitfish S. corallinus. I have kept three of these and found them to be colorful, easy to feed, and non-aggressive to their tankmates.
The most widely seen in the trade is the Foxface Rabbitfish S. vulpinus. They hail from the Western Pacific Ocean and can reach a size of eight inches (20 cm) in closed systems, and slightly larger in the wild. Their captive diet should be varied, i.e., consist of both meaty and vegetable matter. Those that I’ve maintained ate mostly green foods such as nori (dried seaweed/kelp), Spirulina flake, and various frozen herbivore foods. However, they also consumed meaty foods such as adult brine shrimp and mysis shrimp. In my aquariums that contained various types of algae, both desirable and unwanted, they browsed the growths like cows all day. And in the late evening hours they would lose most of their color and get quite blotchy looking. They all seemed to have a favorite place in the aquarium to rest for the night where they either laid on or against some aquarium rock or corals where water flow was quite gentle. When daylight arose, they became colorful again and resumed their browsing on various alga growths.
I’ve also kept S. magnifica, the Magnificent Rabbitfish. It looks quite similar in coloration and shape as the Foxface, and is identical in shape, yet can get about an inch (2.5 cm) longer. In fact, it was sold to me as a ‘Foxface’ Rabbitfish. But it lacked the lower black throat coloration. It was kept in a past 120 gallon system that consisted of various live forms of invertebrate and rock brought back from some diving trips to Mexico. In fact this system was quite nutrient rich and had many forms of algae both desired and unwanted. It also had a very deep sandbed that consisted of very course beach sand that was also collected in Mexico. All in all, this rabbitfish was quite peaceful with various invertebrate and other fish and basically had the same appetite and habits as the previous discussed Foxface.
Even though most aquarists think of all rabbitfish as being a huge consumer of algae, I found the Blue-spotted Rabbitfish S. corallinus, a species that showed little interest in any live form of alga. I kept this species in a 60 gallon reef system and found it to be peaceful and well behaved in mixed company. Yet it showed no interest in any form of algae including nori, except that of Spirulina flake food, which it ‘occasionally’ consumed. Nevertheless, it gobbled down mysis and brine shrimp like it was going out of style and was always first there when these foodstuffs entered the water. When this aquarium entered the sunset mode of lighting, this Rabbitfish would find an area near some coral very near the surface and lay there on its side and become blotchy gray in color. It would stay there all night in this moonlight lit aquarium until the first rays of light entered my office windows the following morning. It then resumed its normal coloration and began to swim leisurely throughout the aquarium, occasionally finding something to pick on, however, not algae. I should mention that a full-grown specimen could attain 10 inches (25 cm), yet most aquarium specimens do not reach this length. My specimen was only about five inches, and a 60 gallon tank sufficed, but would recommend a 100 gallon tank be considered for a larger specimen.
In closing, these are all quite easy to maintain and with most being a large consumer of algae and disease resistant, they make good additions to both fish only and most reef systems. It is also said some species are not safe with some soft corals such as Xenia. Yet I have not personally witnessed such behavior. And keep in mind they have venomous dorsal and anal fins and that care must be taken when handling these fish.