This article originally appeared in Tropical Fish Hobbyist magazine Volume XLII Number 7, March 1994. All rights reserved by the TFH. Permission to reproduce is granted by the publisher to The Breeder's Registry and is not transferrable.
HANS ESTERBAUER
Photos by the author
The angelfishes are the delight of marine aquarists, probably because many species are both hardy and colorful. In particular, many of the smaller species are kept. Let's take a brief look at angelfishes in general and then focus on a particularly interesting small species, Genicanthus caudovittatus.
The angelfish family, Pomacanthidae, is represented in the Indo-Pacific by about 65 species and in the Atlantic by about nine species.
A male Zebra lyretail angel, Genicanthus caudovittatus. |
Genicanthus, usually known as lyretail or swallowtail angels, hold a unique position within their family because they, in contrast to the remaining angelfishes, exhibit pronounced sexual dimorphism.
The angelfishes of the genus Genicanthus - nine known species at present - are distributed throughout the Indo-Pacific, including the Red Sea. These angelfishes prefer depths below 100 feet, and this is probably also the reason why they were first imported only about 15 years ago. They are fairly difficult to observe in their natural habitat.
The zebra lyretail angel, Genicanthus caudovittatus, lives along the coast of East Africa and into the Red Sea. It favors the zones on either side of the reef beginning at a depth of about 115 feet. I was able to observe its unusual behavior in the Gulf of Aqaba, at the Eilat Underwater Observatory and Aquarium, and at Aqaba Marine Science Station.
Genicanthus caudovittatus grows to a length of up to 10 inches, but is usually seen smaller. The body is narrow and humpbacked. As the common name indicates, the tail fin is crescent-shaped and the fin rays greatly elongated. The two dorsal fins merge into each other without a break. The pectoral fins are fan-shaped and transparent.
The female G. caudovittatus differs markedly from the male. Genicanthus species are unique among the angelfishes in displaying pronounced sexual dimorphism. |
As was mentioned above, the sexes differ considerably in color and markings, so that for a long time they were thought to belong to separate species. The ground color of the female is pale lavender gray, becoming lighter toward the belly. The fin edges are darker than their bases. A broad dark bar extends from the upper edge of the eye to the base of the dorsal fin. The caudal fin is edged in black, and the upper black stripe begins in the middle of the body below the dorsal fin. The remaining fins are unmarked and transparent bluish.
The male has considerably more contrasting coloration. Their ground color is bluish white, from which more than 20 black vertical stripes with yellow speckling stand out sharply. They cover the top of the head to about the level of the eye and extend from the back and across the sides to the top of the belly. The breast is adorned with a bean-shaped black spot. The remaining spiny rays of the dorsal fin are yellow, and the soft rays are bluish with yellow speckles. The soft rays of the tail and anal fins are light blue-gray with small yellow spots. The long fin rays of the caudal fin are dark. The pelvic and pectoral fins are transparent, and the caudal peduncle is speckled with orange. Young zebra lyretail angels do not have the typical juvenile markings of the remaining angelfish species, but instead resemble the females.
In its living space, the territory of G. caudovittatus is centered on the coral reef. Whereas the slightly smaller females live in schools and also seek out open water, the males are solitary and. spend more time near the bottom.
The zebra lyretail angel feeds on plankton. In the late afternoon hours, when the water is particularly rich in plankton, they hover as much as 15 feet off the bottom and snatch the larger zooplankton from the water. When threatened they take refuge within the structure of the reef like a flash. Genicanthus caudovittatus, like all angels, is diurnal (day-active) and takes shelter in the reef at night. The angels are agile and lively swimmers that need a lot of swimming room. Nevertheless, from time to time they also rest in crevices.
Comprehensive long-term studies - mainly by Dr. John E. Randall - have shown that the sexes are not genetically fixed. All Genicanthus species, as well as the pygmy angels of the genus Centropyge species, are protogynous hemaphrodites (female-to-male sex change). In the course of the sex change, the testicular tissue grows in the space vacated by the degenerating ovaries. Within a given group of angels, this sex change is triggered by the absence of a dominant male. The strongest female then develops into a male. In the course of the sexual transformation, a change in behavior also occurs. The new male begins to court the females and display typical male territorial behavior. This behavior has a feedback effect and helps complete the transformation so that the male is fully functional. A sexual transformation of this kind is highly advantageous for the survival of the species - the many females produce a large number of offspring; males, however, are produced only as needed.
Up to now, as far as I have been able to determine, little has been learned about the reproductive behavior. Debelius [in Aquarien Magazin, 14(6):272-277] observed a behavior in the Gulf of Aqaba that he interpreted as courtship: A male, swimming alone, suddenly shot toward a female, positioned him-self across her path, and trembled his whole body violently. In so doing he spread his fins and beat vigorously with his tail fin. The event lasted only a few seconds, since in most cases the other females of the group drove off the intruder.
Although G. caudovittatus will not be a problem for the experienced marine hobbyist, in some countries it is subject to a ban. The absurdity of such regulations will not be discussed further here.
A tank of at least 70 gallons is desirable. The water values are also of decisive importance. Temperatures between 75 and 78 F, a pH of about 8.2, and a density of 1.025 are recommended. Best suited for the planting are marine algae of the genus Caulerpa, including Caulerpa sertularioides, Caulerpa prolifera, and so forth.
In summary, it can be said that Genicanthus caudovittatus is not as widely kept as it should be, for it is hardy and long-lived. It is important to keep the fish singly, if possible - even though a few aquarists are successful with compatible pairs - and to feed it a varied diet. As long as the water conditions are always first-rate, disease is rare.
