Thanks to the anonymous tipster who texted me and said “SA Moorish Idol” the other day – wow. Here’s another of our “doomed fish”, the “expert-only, only if you’re a glutton for punishment”, being marketed as something somehow better than the traditional wild-caught specimens.
Captive-bred Moorish Idols (Zanclus cornutus)? Let’s not confuse these as being captive-bred, they most certainly are not. Tank-Raised? Again, Sustainable Aquatics is careful with their terms, as they have marketed the specimen above as “Tank-Conditioned” (sometimes also termed captive-conditioned). The listing of Moorish Idols by Sustainable Aquatics warranted an immediate email for more information.
Matt Carberry, president of Sustainable Aquatics, provided some more information.
These ones were shipped to us at maybe 3 inches long. Just to avoid any confusion, [they] were marketed by us to our customers as tank-conditioned rather tank tank-raised because of the larger size that they arrived. Still very cool, but not what we really want—finding where the tiny Moorish Idols hang-out immediately post-settlement would be a big step toward being able to offer them as tank-raised.
It is well known that post-larval, post-pelagic Acanthurids (Tangs) and the related Zanclidae (the Moorish Idol) do not settle at small sizes. Matt’s email touched on that point – “I’m not sure how small they are when they complete the acronurus stage, but if they’re like [tangs], it’s probably between one to three inches (2-7 cm), larger than most may think.” Indeed, see the example below of a Postlarval Sailfin Tang, already almost one inch long when it finally settled to the reef in Fiji.
Before we just go with the “captive-conditioned” label, let’s keep an open mind. Some quick internet searches turned up some interesting information. A book entitled The larvae of Indo-Pacific Coastal Fishes, which I could browse through Google books. That provided insight into the possible larval history of the Moorish Idol. And here’s the possible smoking gun, originally attributed to P. Dougherty in Reef Sites, published 1995. “Size of largest examined pelagic specimen, 49.0 mm (although individuals may be as large as 75 mm at settlement)”.
It doesn’t take a rocket scientist to do the math; we know that pre-settlement Moorish Idols are documented as being as large as 49 mm – roughly 2 inches, and individuals may be as large as 75 mm, about three inches, or roughly the exact size that Sustainable Aquatic’s “tank-conditioned” Moorish Idols were delivered at. What does this mean? It means that it is possible, but not definite, that the 3″ Moorish Idols shipped may actually represent the recently settled post-larval Moorish Idol, and that could translate to our generally accepted definition of “tank-raised”!
In general, tank-raising, if done truly properly with very young post-larval fishes, has the very real benefit of imprinting fish onto aquarium feeds vs. their natural diets, which can mean a normally corallivorous Butterflyfish can be purchased eating pellet foods. Or perhaps in this case, a very sensitive fish whose diet is normally sponges, tunicates and algae, might be able to thrive on standard aquarium fare. Indeed, Matt relayed that “They are eating SA hatchery diet and pretty much everything else offered”.
Will Carberry’s Sustainable Islands division find those mythical larval Zanclus, or have they already done so? Certainly, the lucky aquarists who receives these very special Moorish Idols are tackling a tremendously challenging species with a headstart!
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