Often, those are the words an aquarist
first mutters when he sets his sights on a Congrogadus.
Unfortunately, the retailer doesn't usually have an answer
for the hobbyist, or worse yet, offers a guess ranging anywhere
from an eel to a blenny and everything in between. Ironically,
the common name for most hobbyists is, in fact, eelblenny.
Even when retailers give the correct identification, they
often are unsure of themselves and are rather vague with the
answer. "Some sort of dottyback," really doesn't
begin to describe fish from the genus Congrogadus,
also sometimes called wolf eels in the aquarium trade.
The Green Wolf Eel typically rests its body along the substrate
and keeps
its head elevated higher than the rest of its body by several
inches.
Photo by Henry C. Schultz III.
Meet the Family
In classifying this group, Godkin and Winterbottom
(1985) moved Congrogadus and the other seven genera
(see Figure 1) of the subfamily Congrogadinae out of the family
Blennidae and placed it underneath the family Pseudochromidae.
In other words, fish that were once thought to be blennies
became dottybacks.
Congrogadinae:
|
Blennodesmus
|
Congrogadus
|
Halidesmus
|
Halimuraena
|
Halimuraenoides
|
Haliophis
|
Natalichthys
|
Rusichthys
|
Figure
1.
The genus Congrogadus was further
divided into three subgenera. Three species were assigned
to the subgenus Congrogadoides, two to the subgenus
Congrogadus, and one species, C. winterbottomi,
to the subgenus Pilbaraichthys. Congrogadus species
differ from their other seven Congrogadinae brethren by lacking
a shoulder spot, and instead having a similar spot found on
the operculum. They also have a higher dorsal fin and anal
fin ray count than all but one of the other species (Halidesmus
may have up to 90 fin rays). Whereas some other Congrogadinae
have three complete lateral lines, Congrogadus only have a
single shortened lateral line. Furthermore, Congrogadus
(Congrogadoides) differ by having the gill membranes
fused to the isthmus. The gill membranes of Congrogadus
(Congrogadus) are not fused, and both Congrogadus
(Congrogadus) and Congrogadus (Pilbaraichthys)
have a posterior otic sensory canal pore (Winterbottom, 1985).
§
amplimaculatus |
§
malayanus |
§
spinifer |
§
hierichthys |
§
subducens |
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Did I just hear you question what a posterior
otic sensory canal pore is or ask what it does? Today is your
lucky day - I had no clue myself! So, I took the liberty of
e-mailing Dr. Winterbottom to ask him about this quandary.
In short, the otic sensory canal pore is believed to assist
with the fish's motion detection system. He was unsure, however,
exactly how this pore worked or why only three of the six
species of Congrogadus have this feature.
Normally, wolf eels will keep themselves buried into
rockwork with only their head poking through waiting,
searching for food. Photo by Henry C. Schultz III.
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In the Wild
All Congrogadus species are rather
secretive fish. Therefore, little is actually known about
their habits in the wild. Additionally, most of the species
have a restricted geographic distribution. For instance, C.
hierichths, a species with a relatively large distribution
for the genus, is limited to the Philippines, while C.
amplimaculatus is found only in the Gulf of Carpentaria.
In contrast, C. subducens, which has the largest distribution
of all Congrogadus, can be found throughout all the
tropical waters of Australia, stretching north through the
waters surrounding Sumatra, the Philippines, Taiwan and Japan.
Congrogadus (Congrogadus) subducens in the author's
home aquarium.
Photo by Henry C. Schultz III.
Because of their secretive nature in the
wild, little is known regarding the depths they typically
inhabit. While C. winterbottomi has been found only
in less than two feet of water, C. spinifer specimens
have been trawled from depths of nearly 200 feet. As a whole,
however, it appears that most Congrogadus species prefer
depths of less than 10 feet, or at least that seems to be
the most frequent depth from which they have been collected.
These tropical wolf eels consume crustaceans
of all sorts. (As a point of order, there is another group
of fishes called "wolf eels" found in the NE Pacific.
These fish get to be about 8 to 10 feet long.) The vast majority
of their diet is composed of shrimps and crabs, but the larger
specimens will also readily consume fish, if given the chance.
They have large mouths, allowing them to swallow prey items
many times larger than expected.
Although most congrogadids are known to
be protogynous hermaphrodites, Congrogadus (Congrogadus)
subducens may be the exception to this rule. Females
of this species which are over 300 mm in length have been
noted to possess small gonads. This all but eliminates the
possibility of them being protogynous hermaphrodites. Despite
this, all congrogadids do lay their eggs in a small clump.
The eggs are unique to the genus in that they are each attached
to a small hook with a thin thread. Once the eggs begin to
break away from the small clump, the hook then falls from
the egg and hangs below, while remaining attached to the egg
by the thin thread-like material. Several authors report that
the hook appears as a grappling hook hanging below the egg
at this point (Winterbottom, et al. 1984).
In the Home Aquarium
The captive care of wolf eels can be considered
rather simple. Like most dottybacks, they have only a few
basic needs, and if those needs are met, they can be nearly
bulletproof. Oddly enough, however, the personalities of these
captive fish do not mimic the behaviors which researchers
report about wild specimens.
Once acclimated to an aquarium, wolf eels
are anything but secretive. Although they will spend
the vast majority of their time imitating an eel and sticking
their face out of a crevice or cave, they will, in fact, be
the first fish to the food when it's offered, and will often
greet the owner at the surface any time the aquarist stands
near the aquarium. I think this is solely because they are
looking for food. Regardless, they have one of the more outgoing
personalities of aquarium fish.
But are they reef friendly? Well, I guess
that depends on your definition of reef friendly. After
all, they will not bother any sessile invertebrate. On the
other hand, if it has fins or legs and it moves, it better
be bigger than the wolf eel's mouth, which will undoubtedly
make an attempt to swallow it! The appetite of wolf eels is
overwhelming. Basically, it will be impossible to keep hermits,
crabs, or shrimp in the same aquarium with these fish; they
will become a quick meal for the wolf eel. Only fish considerably
larger than the mouth of the Congrogadus have a fighting
chance. New additions to the aquarium will quickly be 'sized
up' by the wolf eel. If they do not fit in the eel's mouth
the first time, they will generally be left alone, though
it is likely the wolf eel will continue to monitor the relationship
between its mouth and the overall size of its tankmates. Finally,
as juveniles, wolf eels can easily be hunted and preyed upon
as well. Large morays, toadfishes, or any other large predators
can easily reverse the prey/predator role and consume a juvenile
wolf eel. Take great care in mixing species with appropriate
personalities, always bearing in mind their respective mouth
size.
|
|
Surgeonfish (top) & Rabbitfish (bottom)
are wise choices as tankmates for
Congrogadus species, assuming they are larger than
the wolf eel's mouth.
Photo courtesy of Patti Beadles (top) and Greg Rothschild
(bottom).
Compatibility
chart for Congrogadus:
Fish
|
Will Co-Exist
|
May Co-Exist
|
Will Not Co-Exist
|
Notes
|
Angels, Dwarf
|
|
|
X
|
Most dwarf angels will be too small and will be eaten.
|
Angels, Large
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Anthias
|
|
|
X
|
Will likely be eaten.
|
Assessors
|
|
|
X
|
Will likely be eaten.
|
Basses
|
|
|
X
|
Will likely be eaten.
|
Batfish
|
X
|
|
|
Adult batfish will mix well.
|
Blennies
|
|
|
X
|
Will likely be eaten.
|
Boxfishes
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Butterflies
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Cardinals
|
|
|
X
|
Will likely be eaten.
|
Catfish
|
|
X
|
|
Juveniles of either species may be harassed or eaten
by adults of the other species.
|
Comet
|
|
|
X
|
Will likely be eaten.
|
Cowfish
|
|
X
|
|
Acquire adult cowfish.
|
Damsels
|
|
|
X
|
Will likely be eaten.
|
Dottybacks
|
|
|
X
|
Will likely be eaten.
|
Dragonets
|
|
X
|
|
Though it may be expelled each time, it will likely
be harassed regularly.
|
Drums
|
|
X
|
|
Acquire adult drums.
|
Eels
|
|
|
X
|
Some morays may feed on the wolf eel.
|
Filefish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Frogfish
|
|
|
X
|
May try to eat each other.
|
Goatfish
|
|
X
|
|
Acquire adults of each species.
|
Gobies
|
|
|
X
|
Will likely be eaten.
|
Grammas
|
|
|
X
|
Will likely be eaten.
|
Groupers
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Hamlets
|
|
|
X
|
Will likely be eaten.
|
Hawkfish
|
|
|
X
|
Juvenile hawkfish may be eaten.
|
Jawfish
|
|
|
X
|
Will likely be eaten.
|
Lionfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Parrotfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Pineapple Fish
|
|
X
|
|
Acquire an adult pineapple fish.
|
Pipefish
|
|
|
X
|
Will likely be eaten.
|
Puffers
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Rabbitfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Sand Perches
|
|
X
|
|
Acquire an adult sand perch.
|
Scorpionfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Seahorses
|
|
|
X
|
Will likely be eaten.
|
Snappers
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Soapfishes
|
|
X
|
|
Acquire adults of each species.
|
Soldierfish
|
|
X
|
|
Acquire adults of each species.
|
Spinecheeks
|
|
|
X
|
Will likely be eaten.
|
Squirrelfish
|
|
X
|
|
Acquire adults of each species.
|
Surgeonfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Sweetlips
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Tilefish
|
|
|
X
|
Will likely be eaten.
|
Toadfish
|
|
|
X
|
Toadfish will eat juvenile wolf eels.
|
Triggerfish
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Waspfish
|
|
|
X
|
Best for a specialty aquarium.
|
Wrasses
|
X
|
|
|
Good choice, assuming it won't fit into the mouth of
the wolf eel.
|
Note: While many of the fish listed
are good tank mates for Congrogadus species, one should
research each fish individually before adding it to the aquarium.
Some of the fish listed above are better left in the ocean
or for advanced aquarists.
Smaller species, such as grammas and dwarf angels, are best
kept out of a wolf eel's tank.
Photo by Mark Ridley (left) and Greg Rothschild (right).
For foods that you will intentionally feed
the wolf eel, stick to a diet for carnivores (obviously).
Countless types of food products on the market are geared
towards the diet of groupers, eels, and puffers. Such foods
include prawn, squid, silversides, and crab, among others.
These foods are ideal for the wolf eel, too. Also, bear in
mind that a wolf eel will keep eating as long as it's fed.
Thus, take great care not to overfeed. Simply feeding a single,
large portion per day will be adequate.
Shrimp and crabs are likewise best avoided in a tank housing
a wolf eel.
Photo by Hitoshi Takakurra (left) and Chuck Fiterman (right).
As always, correct water parameters go
a long way toward maintaining the long-term health and maintenance
of a wolf eel. If this fish is going into a reef aquarium
containing live coral, there need be little concern for proper
conditions, because corals are far less tolerant of adverse
conditions than the Congrogadus species. If a fish-only
tank is the intended target aquarium, ensure that its water
parameters fall within these general guidelines: 1.022 - 1.025
SG, 0 nitrates, nitrite, and ammonia, and a water temperature
of 78 - 84°F.
Providing adequate rockwork and aquascaping
is important, especially for new additions. The wolf eel will
attempt to hide when first introduced; this should be expected.
Eventually, the aquarist should begin to see it strike poses
similar to that of moray eels - with just the eyes, nose,
and mouth extending from the crevice or den. Over the course
of a week or two it will typically become more outgoing. It
should also be noted that these fish have a tendency to become
bored, much like an octopus, and will continually search the
aquarium. Sadly, the end result is often a wolf eel that finds
its way to the carpet. Keep aquariums containing wolf eels
covered!
Meet the Species
As much as I would like to introduce all
six species of this genus, there really is no good reason
to do so. All six look very similar, and usually only one
species will show up at local retailers. Therefore, I'll concentrate
my discussion on that species.
The most commonly collected Congrogadidae
for the hobby is undoubtedly Congrogadus (Congrogadus)
subducens. This species is collected so frequently, relative
to the other species in its genus, that it has been given
the same common name as the genus. Sometimes retailers try
to be original, though, thus one may see it sold as the Green
Wolf Eel rather than simply calling it a Wolf Eel. Despite
being given this common name, color variation of this species
is well documented. Depending on exactly where the specimen
was collected, colors of green, brown, red or even yellow
may be seen (Herre, 1939). In any case, expect these fish
to become very large (this is the largest congrogadid) as
these fish may attain lengths of around 15 inches or slightly
more. This large size should highlight the warning flag offered
above: they are fish eaters! Because of their reclusive
nature, they typically will not need an aquarium as large
as their size would indicate. A typical 75 gallon or 90 gallon
aquarium containing ample amounts of live rock should provide
an adequate home. Although Congrogadus (Congrogadus) subducens
almost always has a spot on the operculum, some specimens
lack this spot. Additionally, this species is the only Congrogadidae
lacking a dorsal spine.
Conclusion
The next time you spot a wolf eel at your
local fish store, you will now not only have the information
you needed to help decide whether or not it would be a wise
purchase, you should also be able to tell the store employees
quite a bit about it. A wolf eel can make an interesting addition
into the right aquarium. Their overall character measures
up to be one of the most personable fish available in the
hobby. In some aquaria, however, these fish can be an aquarist's
worst nightmare. Hopefully, the information presented here
has precluded the development of the latter situation.
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