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Amongst the large aquarium fish family of Butterflyfishes are a few "standards" that epitomize what's best in captive specimens. Such is the case with the threadfin; this readily available species is among the easiest of marine fishes to keep. Aurigas will feed on arrival on the widest variety of prepared and fresh foodstuffs, and are near the top of the B/F (industry shorthand for Butterflyfish) list in disease resistance.
The threadfin is quite variable in coloration and body shape over its wide range, and a number of "accidental" hybrids have been reported. Though most specimens offered are excellent, here I'll offer you my opinions on picking out the best.
Classification: Taxonomy, Relation With Other Groups
The threadfin is one of 92 species in the giant genus Chaetodon, of the Butterflyfish family Chaetodontidae of ten genera and some 120 nominal species. As you will find, this assemblage has many species offered to the hobbyist, some good, some not.
Chaetodon auriga, the Threadfin Butterflyfish, is found widely throughout the tropical Indo-Pacific, eastward to my favorite source, Hawaii, westward to the Indian Ocean including the Red Sea. Specimens from the last are especially gorgeous and hardy. Thank goodness that collection and shipment from the Red Sea has become reasonable in terms of available specimens and lowered cost.
Color and pattern-wise threadfins bear perpendicular bands of black lines on bright white bodies with or without a black spot on the dorsal fin. A dark eye-band obscures that sensitive area from attack and the upper rear portion of the fish is painted in a golden yellow.
Chaetodon auriga's common name stems from a dorsal filament composed of the fifth and sixth filament of the soft dorsal; this "thread" grows with increasing fish size.
Captive records of threadfins tip nine inches, total length; they rarely reach such magnificent proportions in captivity.
Selection: General to Specific
The following criteria must all be considered together in determining a specimens suitability.
How long has your dealer had the fish? This species is generally excellent on arrival, but I suggest holding off purchasing all butterflies for a good week or two after arrival.
Too small or large butterflies adapt poorly. Choose ones between 3 and 5 inches if possible.
This is a rule of thumb for any animal purchase, especially with chaetodonts. How beat up and traumatized they've been through capture and transport is best judged through a feeding assay.
Reddening of the mouth or fin bases disqualifies a prospective purchase. Due to their sharp pointed snouts, threadfins, indeed all B/Fs need to be packed in large bags and laid on their sides in transit. This provision reduces the chance of damage from slamming during handling and shipping.
Collecting Your Own
These and most all other Butterflyfishes are collected using a "barrier net" arranged as an impenetrable barrier. Prospective areas are corralled, specimens driven in and hand netted off the barrier net.
Raccoon Butterflies live in shallow regions of coral reefs; with both ready holes to swim in/out and dive into, and plenty of open space. Note that these species can and do get pretty big (more than hand size), and don't tolerate crowding; a small specimen requires a good fifteen gallons itself, a larger individual a minimum of thirty.
Butterflyfishes do not appreciate concentrated metabolites in their water such as nitrite or nitrates; however they do best in established (six months plus) aquariums that are well filtered with tools for maintaining low organic concentrations (e.g. fractionation, chemical absorbers).
High consistent pH (in the 8's), temperature (75 F. plus), and oxygen (aeration, vigorous circulation) are requisite for Aurigas, as is a stable specific gravity in the 1.020s.
Threadfin butterflies are most often seen in pairs or singly, only occasionally in small groups. However, unless you purchase or capture them together yourself, they are best kept one to a tank.
Other Butterflyfish family members may fight if closely matched size and shape-wise or if the system is overcrowded. I suggest keeping an inch or so difference in your new chaetodonts and introducing the smallest first, with a few weeks span between new specimens.
Due to their spiny-ness, these BF's are generally left alone. The only potential problem comes from the usual "wise-guys" and the Aurigas trailing dorsal filament.
Reciprocally Chaetodon auriga "live and let live" with the excepting of edible non-vertebrates; they are definitely not for reef set-ups.
Reproduction, Sexual Differentiation/Growing Your Own:
Chaetodonts are egg-scatterers, releasing their sex cells to the mid-water column cued by the moon and tides. Larval young go through a remarkable armored "tholichthys" stage as free-floating plankton, settling down weeks to months later as miniature adults. All specimens offered are wild collected.
Threadfins are often encountered as pairs in the wild; they are indistinguishable sexually.
As an interesting reproductive note, Chaetodon auriga hybrids have been reported between it and Chaetodon lunula, the raccoon B/F (Campbell 1980), and the Saddleback, Chaetodon ephippium (Burgess 1978).
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
In the wild stomach-contents analysis reveals that threadfins feed on a mix of non-vertebrates (worms, snails, crustaceans), algae and coral polyps. In captivity they have proven to be non-finicky eaters of freeze-dried, fresh and frozen/defrosted meaty foods (plankton, shrimp, shellfish, fish fillet).
Live brine shrimp or Tubifex works well to encourage feeding in new specimens and their is nothing like a freshly opened clam to "bulk up" a thin individual.
As with other all-day "browsing" species, this butterfly is best fed small amounts at least twice daily.
Disease: Infectious, Parasitic, Nutritional, Genetic, Social
The auriga is typically parasite free on import, with the possible exception of gill flukes. They are susceptible to the twin protozoan scourges of marine aquarium keeping, but respond well to conventional treatments for the same.
A standard quarantine and/or dipping in freshwater with or without other chemicals will preclude you having to do any treatment period.
The Threadfin Butterflyfish is definitely one of the best of the family; it gets my vote as a great beginners "first marine fish"; for being a ready feeder on all types of foods, easily adapting to aquarium conditions, disease resistance, and sheer beauty.
Allen, Gerald R. 1979. Butterfly and Angelfishes of the World. Vol. 2. Aquarium Systems, OH. 203 pp.
Burgess, Warren E. 1978. Butterflyfishes of the World; A Monograph of the Family Chaetodontidae. T.F.H. Publications, NJ.832 pp.
Campbell, Douglas 1980. Marines: Their care and keeping. Butterflyfishes: Part one. FAMA 10/80.
Emmens, C.W. 1985. Keeping chaetodonts. TFH 5/85.
Fenner, Robert 1996. Butterflyfishes you don't want. TFH 9/96.
Hoover, John 1995. Hawaii's Butterflyfishes, pt. 1. FAMA 11/95.
Hunziker, Ray 1992. The ten best butterflies. TFH 6/92.
Moenich, David R. 1991. The Butterflyfishes. AFM 1/91.
Nelson, Joseph S. 1994. Fishes of the World. Wiley, NY. 600 pp.
Refano, Joe 1983. The importer speaks; the Butterflyfishes part 2., Indo-Pacific Butterflyfishes. TFH 11/83.
Steene, Roger C. 1977. Butterfly and Angelfishes of the World. Vol. 1 Australia. Aquarium Systems, OH. 144 pp.