Figure 1. A male green wolf eel blenny.
It's well understood
that the fish we have in our home aquariums originated in
one of the many oceans of the world and that these fish were
collected from the wild, shipped across continents, and finally
end up at a local fish store. Hopefully, we also have an appreciation
of the hardship suffered by these fish due to wild collection
and that many of these fish populations will ultimately not
support unlimited and unregulated harvesting without vanishing.
Given this, the time is now for many home aquarists to act
in regards to reducing the demand for wild caught fish by
aquaculturing fish as part of their home efforts. In fact,
many hobbyists are beginning to do just that; there are a
number of commonly available clownfish species (Amphiprion
sp.) that are being home bred with great success. Banggai
cardinalfish (Pterapogon kauderni) are another species
commonly bred as part of ongoing home-based breeding efforts.
Most importantly, breeding and raising the fry of these fish
is not out of the grasp of many aquarists with limited aquarium
experience, and as more commercially available first foods
for fry become commonplace, breeders should expect to be increasingly
successful with additional marine ornamental fish. Back in
April 2004 as part of the Fish
Tales column, Henry Schultz described the family Congrogadus,
i.e., "wolf eels," a family little known to most
hobbyists, yet this fish is perfectly suitable for home breeding
efforts and makes an interesting and hardy addition for the
aquarist who keeps fish-only tanks.
This fish from the Indo-West Pacific is
neither an eel nor a blenny (and most certainly not a wolf).
Other common names include the carpet eel blenny or just plain
ol' eel blenny. As described in detail in Fish Tales 2004-4,
this fish is a member of the Pseudochromidae (Dottyback) family.
Attaining a full-grown length of 45cm
makes it one of the largest in that family; Pseudoplesiops
typus is the largest, reaching 46cm.
One useful attribute of this fish is that it is sexually dichromatic;
meaning the males (figure 1) are green, while the females
(figure 2) are a more drab gray/brown with a pinkish hue that
seems to vary in intensity. Additional species descriptions
can be found
here and here.
Figure 2. A female green wolf eel blenny.
The wolf eel blenny has a temperament and size that would
prohibit keeping it in most reef tanks. In fact, I highly
recommend this fish be kept with other larger aggressive fish
that cannot fit into its cavernous mouth; however, wolf eels
generally do best in a species-only tank. The wolf eel blenny
is occasionally collected for the trade and can be found for
sale at local fish stores or online retailers. In its natural
habitat of shallow reef areas, this fish prefers to inhabit
rocky crevices where it can easily lunge out at unsuspecting
Even though this fish attains an adult size of around 18
inches, it doesn't require a lot of room to feel comfortable
or to breed in captivity, as this fish acts very eel-like,
usually projecting its head from the rockwork or hiding behind
rock outcrops. In one particular instance, I know of a hobbyist
who had a pair that spawned in a 30-gallon tank. To make this
fish feel at home the aquarium should be set up with plenty
of rockwork, creating caves where it can lurk waiting for
its next meal to pass by. The wolf eel should be fed plenty
of meaty foods. When first acquiring this fish, it will readily
accept live feeder fish and crustaceans (such as ghost shrimp)
but, given enough time, it is not difficult to wean over to
dead or prepared foods and should be fed to satiation two
or three times weekly. Rapidly growing juvenile wolf eels
can be fed smaller, more frequent meals daily. If properly
fed, these fish prove to be hardy tankmates; however, my experience
also suggests that they do not hesitate trying to consume
a new tankmate if the new fish "appears" to be the
right size to fit into its mouth.
The spawning ritual of C. subducens is similar to
most dottybacks. The female lays eggs in a ball-shaped mass,
which the male fertilizes and then guards by wrapping his
body around the egg mass. Little information is available
from the literature regarding this fish's spawning behaviors;
suffice it to say that the information presented here will
be composed of a summary of experiences from a few different
hobbyists that have been fortunate enough to create spawning
pairs. However, be advised, as with most fish, it seems that
getting the fish to spawn is the easy part; raising
the fry is the biggest challenge. For some reason (and I am
not discounting luck) I have been the only person I know who
has been able to successfully raise green wolf eel fry.
The wolf eel blenny is a seasonal spawner, usually spawning
five or six consecutive times about 10 to 14 days apart and
typically starting around November/December. I don't know
how they sense the change of seasons when they live in controlled,
constant environments with no effort made to simulate the
change, but somehow they do. As noted above, an enormous tank
is not necessary to house a pair of these fish, but there
should be plenty of places for the female to hide, since the
male is the more aggressive/dominant one and is likely to
harass her. In every case of captive spawning that I know
of, the female was the first inhabitant of the tank, while
the male was added some time later. In each case, however,
this was by chance rather than by planning; but I feel it
is important, given the male's more aggressive/dominant role.
I would not be surprised if a female would be killed if she
were added to a tank where a male had first made his home.
Another factor that may be important when pairing up this
species is that the female should be both ready and able to
spawn. The female will produce an egg mass at regular intervals
during the spawning season. When this happens, she can be
observed guarding the nest with her body wrapped around it,
in much the same way the male does, or she will swim around
the tank carrying the egg mass in her mouth, presumably looking
for a male to hand off the egg mass to. When there is a male
present, he will readily take the eggs as soon as the female
produces them, but that is where the female's role ends. The
male defends and protects the nest from any intruder, including
the mother. As mentioned, the male will curl his body around
the nest while periodically shifting, rotating and fanning
it with his fins. He typically keeps the nest in a cave or
dugout area in the substrate.
Figure 3. An egg mass after six days of development.
The nest is an egg mass (figure 3) of approximately 100-200
eggs that are about 5mm in diameter.
The individual eggs appear covered with bumps and stick to
each other creating this mass. Incubation of the eggs occurs
over 14 days, after which fry approximately 10mm
long emerge. It was interesting to observe the fry within
the egg during its development, around the 5th
day, the shape of the developing fry becomes discernible,
and as the days progress, its eyes begin to appear, along
with a red spot in its abdomen, which, I presume, is its heart.
From about the 10th day
onward, the fry shift noticeably within the egg.
Since my wife and I are amateur fish breeders, we have learned
that parental behavioral care can vary widely between specimens
of the same species. Some breeders have reported that the
male cares dutifully for the nest up until hatching and even
then does not actively feed on the newly hatched fry. I was
not that fortunate. The spawning pair that I have worked with
is actually owned by some friends, Doug and Barb Arnold. They
asked for our help in trying to raise the fry (since my wife
and I are known in our area for breeding clownfish) after
they had made a few unsuccessful attempts.
I soon discovered that one of the problems they faced was
that the male was slowly consuming the nest, polishing it
off before the 14 day incubation was complete. This was how
they lost their first two nests. Subsequent nests were taken
from the male a few days after spawning (risking great bodily
harm to do so) and put it in a breeder basket at the water's
surface. Despite keeping those nests in the same tank and
directing water from the filter return over them to keep them
aerated, the next few batches had a very low hatch rate with
most of the eggs turning milky white and becoming infected
with a fungus before they were due to hatch. Combine that
with the parents sucking the hatched fry through the slots
of the breeder basket and eating them, and Doug and Barb didn't
have much to work with. For some reason, the fry that did
survive did not survive for long; all died within one day.
So, after talking to Doug and Barb, we decided to take the
next nest and see what results we could achieve (admittedly,
not much of a plan). Five days after the spawn, we gently
separated the egg mass into one small part for Doug and Barb
to keep while I took the larger portion. The portion I took
was placed into a large fish bowl containing only water from
the parent's tank, and it was aerated so that the nest was
gently moving (see figure 3). Things went well for the first
few days, after which the water quality started to deteriorate
quickly as some of the eggs began dying off. Water changes
of up to 90% were conducted on a daily basis in an attempt
to maintain water quality. In spite of my best efforts, the
nest began to break apart with some of the eggs fouling and
turning milky white. I did my best to keep the dying eggs
removed from the mass, but as the 14th
day approached, things quickly took a turn for the worse.
By the 15th day there was
no hatch, and the nest was slowly deteriorating. I took these
two pictures below; the first (figure 4) is a still viable
egg and the second (figure 5) is a pre-hatch fry whose shell
I had manually removed. On the 16th
day it looked as if this project was going to be a total failure.
Looking into the bowl, I couldn't see any eggs that appeared
to be still viable. I was considering dumping the whole egg
mass down the drain when my wife spotted a newly hatched fry
swimming around in the bowl. We removed the fry and put him
into a separate container with some water from another tank,
and closely examined what was left in the bowl one more time.
It seemed that one was all we were going to get from this
Figures 4 & 5. Left: An egg due to hatch.
The egg shell has become less transparent than earlier in
development. Right: A fully developed fry that has
been manually removed from its shell. Its features are much
more distinct than in the left picture, and a yolk sac can
now be seen.
Figure 6. Junior at 14 weeks old. Judging by
his coloration, I would say that our Junior is a male.
I have been unable to find information about this species'
potential sexual dimorphism, so I suppose this guess
Junior, as he was so aptly named by my wife, was about 10mm
long when born and was very active, making repeated laps around
the fish bowl. It looked just as others have described their
fry: slender, silvery/transparent with big eyes and a large
red spot in his abdomen. Since we normally have a large supply
of rotifers on hand, we tried this as a first food. Judging
from his size we supposed that freshly hatched Artemia
would be small enough, but from the limited information that
I had, it would seem that this hadn't worked well for other
breeders. For the first two days I kept a dense supply of
rotifers in its bowl with some greenwater added to ensure
the rotifers remained nutritious until Junior had a chance
to eat them. It was very hard to tell if it was actually consuming
the rotifers, so I started adding newly hatched Artemia
to the bowl. Junior's belly then gained an orange hue from
eating the live BBS, so I felt that we might have a good chance
at raising him. I believe the difference is that other breeders
tried offering frozen BBS, while we had success using live
ones. In that first week, the fry grew rapidly, gaining about
50% in overall size; the coloration gradually became a more
opaque silver with just a hint of green. Live baby brine shrimp
was the primary food for the next few weeks, and he continued
growing with color patterns slowly developing. As Junior grew,
I started raising brine shrimp to larger sizes and fortifying
them with Selcon before feeding them to him. But, as
anyone who has raised brine shrimp knows, this is something
that is not easily done. I figured since it was only one fish,
it would be easier to capture some mysid shrimp and amphipods,
which were numerous in my reef tanks, to feed him. It seemed
that Junior preferred the mysids and amphipods over the brine
shrimp, as these critters remained on the bottom of the tank
where he typically stayed, precluding a swim up into the water
column to get the brine shrimp. At about one month of age
I decided to try feeding him frozen brine shrimp, which he
took to immediately. Whew! No more siphoning critters from
the bottom of my reef tanks. At the time of writing this article
Junior is 16 weeks old and about 30mm
long. He looks just like a smaller version of his father with
the only exception being that his coloration is not quite
as dark as his dad's. While Junior has been a joy to raise,
I wish we had been more successful incubating the eggs and
had at least 50 more just like him. As we began our rearing
at the pair's last spawn of the season, we will have to wait
until the spawning season of 2005 to make a second attempt
at rearing the fry.
Figure 7. Posing on a quarter for scale.
Figure 8. An overhead shot with a quarter and a test
vial for size reference.
If you have any questions
about this article, please visit my author forum
on Reef Central.