Red Speckled Coral Goby
Caracanthus maculatus

Also known as the Velvet Coral Croucher, the Spotted Coral Croucher, or the Orbiculate Velvetskin. Phew!

If you are the kind of aquarist that likes to get out and about amongst your local retailers in order to see what new specimens they might have, then the chances are that you will have come across the subject of this article.

The red speckled coral goby is not every aquarist’s cup of tea, being small, secretive and with looks that only a mother could love. O.K. so the last comment is not really true as this species is small and endearing with characteristics that many casual observers are likely to refer to as “cute”. If we are completely honest then we must confess that this species is not really that expensive or even particularly rare which are two of the main criteria for inclusion in this column. So what has given the diminutive red speckled coral goby the right to inclusion in the exotic fish keeping series? Well, this is also a column of the unusual and so we should make it clear at this point that this species is not actually a goby – in fact, it is not even closely related to the family Gobiidae. The fine hairy appearance of the lower jaw region and body of the velvet coral croucher gives it its common name.

The Genus Caracanthus is, in fact, an integral part of the family Scorpaenidae that includes scorpionfish, stonefish and their relatives. I short these are groups of fish that are completely different in appearance to the velvetskin. In order to understand why this significant departure from the more or less standard body plan of the rest of the family has occurred we must look at the similarities in the way of life between this species and the goby species that it resembles. Species contained within the Genus Gobiodon are also known as the coral gobies and are specialised for an existence in and amongst the branching skeletons of small polyp stony corals like Acropora and Seriatophora. As a result their bodies have evolved to appear laterally compressed rather than cylindrical in cross-section like most gobies. The pectoral fins are fairly large and are used to pull the goby between branches of the coral. Of course the ability to negotiate the labyrinthine pathways between the branches of corals requires a modest body size and the largest coral gobies only reach 65mm or so.

That the velvet coral croucher resembles these gobies is beyond debate although it certainly does not help that one of the U.K.’s largest marine livestock wholesalers lists this species as the red speckled coral goby. It occupies the same niche in its natural environment as the Gobiodon gobies inhabiting the spaces between the branches of SPS corals. It does not possess a ventral sucker to hold itself in position but the pectoral fins are almost hand-like and well muscled and assist in moving through restricted spaces. Velvetskins are also small with this species attaining a meagre 5cm and the Hawaiian Caracanthus typicus making little more than half of this length.

The similarity between the genera Caracanthus and Gobiodon is yet another example of a phenomenon that zoologists refer to as convergence. Convergence is the opposite of what we might expect from evolution. We tend to think of species diverging from one another where a species or many are derived from a common ancestor. Think about the ever-increasing branches of a family tree for a suitable analogy. Convergence is the antithesis of divergence since it describes the process by which seemingly only very distantly related ancestors give rise to species that closely resemble each other. Such are the problems caused by the presence of the convergence phenomenon that it has been proffered by creationists as definitive proof of a single creator.

Such theological pondering points are well beyond the mandate of Marine World magazine but suffice it to say that this process is relatively common in the world or coral reefs. Our specimen hails from the Pacific Ocean including Indonesia and the Great barrier reef and is very similar to the Hawaiian C.typus of the Hawaiian Islands and C.madagascariensis of East Africa and the Maldives and it is uncertain whether subsequent revisions of the genus will reveal that these “species” are actually geographic variants of the same species with subtle variations in skin tone and patterning. C. unipinna is the only one of the four species that shares its range with another. The so-called pygmy coral croucher has a similar distribution to C. maculates and can be distinguished by the continuous dorsal fin rather than the two separate fins possessed by our specimen.

Maintaining the velvet coral croucher in captivity is relatively easy although the aquarist must be prepared for it to disappear from time to time. Good specimens feed well on variety of foodstuffs including mysis shrimp, artemia and other meaty foods small enough to be consumed easily. In its natural range the predatory family ties of the coral croucher come to the fore as it stalks small invertebrates resident on the host coral. The fish are so dependent upon their corals for shelter that they will not leave them even to remove food items from the water column. In this respect they differ from the true coral gobies significantly and food must be fed directly into the areas in which they are hiding. It is not necessary to house these fish with SPS corals although they are unlikely to do their hosts any significant harm particularly if the colonies are of a reasonable size.

Analysis of the reproductive organs of two species from the Genus Caracanthus has suggested that they are protogynous hermaphrodites, that is that they are females first then males. It may be that if all of the specimens encountered in a retailer’s aquaria are of a similar size then they may be the same sex and are likely to be females. Eggs are thought to be released in floating bundles in common other species in the family with similar ovary structure. We have been unable to establish whether spawning has been reported in captivity but they have for other family members and the maintenance of a pair or small groups quite conceivably could lead to success in this department.

So for a measly £15-£20 you could own a wonderful species of fish that although secretive has many endearing qualities not least the fact that it is not what it first appears. Although the supply is a little hit or miss increased demand for this species might increase the regularity with which it is collected. Ask your dealer about the possibility of getting a couple of these little scorpions but remember, you might have to asked for this fish under its alias- the red speckled coral goby.

References and Suggested further reading:
http://custance.org/old/evol/3ch1.html
http://www.wetwebmedia.com/caracanthidae.htm
Hermaphroditic Characteristics of Gonad Morphology and Inferences Regarding Reproductive Biology in Caracanthus (Teleostei, Scorpaeniformes)
Issn: 0045-8511 Journal: Copeia Volume: 3 Issue: 1 Pages: 68-80