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
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
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
References and Suggested further reading:
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