Matt Clarke highlights the Threadfin trevally, Alectis ciliaris, a species you should most definitely avoid...
Common name: Threadfin trevally, African pompano, Pennantfish.
Scientific name: Alectis ciliaris (Bloch, 1787).
Origin: A very widespread species in tropical waters across the world.
Size: A frankly ridiculous 150cm/5'.
Diet: Crustaceans and fish.
Aquarium: Although undoubtedly an extremely beautiful fish while juvenile (the filaments disappear as the fish gets larger), this is also one of the most unsuitable fish species I've seen on sale for a while.
The Threadfin trevally is a big gamefish found in the open ocean and isn't suitable for anything other than a very spacious public aquarium. I would be incredibly surprised if there was any fishkeeper in the country with a private aquarium large enough to house this fish.
Pete Liptrot of the Bolton Museum Aquarium told PFK: "Although juveniles of this species are undoubtedly eye-catching, it's hard to imagine a species less suitable for the home aquarium. They are fast, active hunters with high metabolisms which will place considerable strain on an filtration system.
"Long before they reach adulthood, they will require an aquarium measured in the tens of thousands of gallons. By the time they are anywhere near to their potential adult size of over a metre, they will require the sort of enclosure which in this country can only be provided by a few public aquarium institutions."
Buyers shouldn't be tempted to obtain them while young with a view to offering them to such an institution at a later date, as this would be highly dependent on this species being part of an overall collection plan (and if so they would probably already have all that they require), and also the institution possessing sufficient reserve quarantine space for an unexpected acquisition. Far better to view this, and similar species, in some of the excellent public aquariums we have in the UK.
Notes: Young specimens have very long filaments trailing from the dorsal and anal fins, which aren't present in adults. The filaments on this one are actually very short.
In many specimens they can be more than 10 times the body length of the fish! I would imagine that they would be vulnerable to nipping and infection, so masses of free swimming space would be needed just for a tiny youngster.
Similar species: Young Alectis indica look similar but have filamentous extensions to the pelvic fins, which are absent in A. ciliaris.
Availability: This specimen was spotted for sale at Shirley Aquatics, Yarnton, Oxford. Fingers crossed that it gets snapped up by a public aquarium. Please don't buy these if you see them on sale.
Price: On sale for 30.
This article was first published in the November 2007 issue of Practical Fishkeeping magazine.