Members of the fish family Holocentridae
will never take home an award for being the most sought after
marine fish. They cannot compare with the remarkable colors
of fairy wrasses, the classic beauty of marine angelfish,
or the puppy-like nature of puffers. Perhaps it is just this
- the lack of beauty or charismatic personality, which makes
the Holocentridae good aquarium candidates. While hobbyists
can travel to countless aquariums stretching across the world,
throughout their travels they will likely become bored seeing
Yellow Tangs, Coral Beauty Angelfish, or (insert any other
common fish). But, in all these loacations Holocentridae species
might be absent from all those aquariums. With a holiday toast
to being unique and swimming against the flow, I present the
unheralded Squirrelfish.
A magnificient photo of a captive Neoniphon sammara.
Photo courtesy of Greg Rothschild.
Meet the Family
The marine fish family Holocentridae is
divided into two subfamilies: Myripristinae and Holocentrinae.
Frizzell and Lamber (1961) and Hecht (1982) concluded differently
regarding this classification, however. They used a combination
of recent and fossilized otoliths to determine that these
two subfamilies should actually be regarded as two separate
families. However, to this day most other authorities still
regard the two as subfamilies. These two subfamilies are known
commonly as the Soldierfishes (Myripristinae) and the Squirrelfishes
(Holocentrinae). Although the two subfamilies appear to be
nearly identical to the casual observer, there are significant
external differences, most notably the preopercle, a bone
in the cheek region. Holocentrids have a sharply angled preopercle,
which has a long spine at the corner. In many species this
spine is venomous (Randall, 1998). The Myripristids lack this
spine in most cases, but some species may have one short,
broad, non-venomous spine. Of course, there is an exception
to this rule; the monotypic Corniger spinosus has 1
- 2 sharp spines. In addition to the spine, Holocentrids have
a narrow mucous channel, compared to the wide mucus channel
of Myripristids (Randall, 1998).
|
All squirrelfish have a sharply angled preopercle with
a long spine at the corner, which is easily viewable
in this photo. Although they are close relatives, Soldierfish
lack this spine. Photo courtesy of Greg Taylor.
|
Holocentrinae has three genera, Holocentrus,
Neoniphon and Sargocentron. Thirty-three species
are now classified as Sargocentron (see below), though
it took several revisions to arrive at this current classification.
Fowler (1904a) initially launched the subgenus of Sargocentron
and placed it within the Holocentrinae. After additional investigation,
Fowler (1944) forty years later, raised Sargocentron
to genus level. Later, however, Woods (1955) disagreeing with
Fowler's interpretation, ignored this revision and referred
to Sargocentron as a subgenus of Holocentrus.
Adding to the confusion, when Shimizu and Yamakawa (1979)
concluded their review of Holocentrinae, Sargocentron
was not included at any level. However, Matsuura and Shimizu
(1982) concluded Adioryx and Sargocentron were
congeneric. Adioryx was originally described by Woods
(1965) with the western Atlantic Adioryx poco. Sargocentron,
having been originally described 61 years prior to Adioryx,
takes precedence and therefore Adioryx is a junior
synonym of Sargocentron.
Flammeo is often used instead of
Neoniphon because Woods and Sonoda (1973) used this
name in preference to Neoniphon, because Neoniphon
was "based on a species whose status is uncertain."
However, the original description of Neoniphon by Castelnau
(1875) is accurate, and thus Flammeo is a synonym of
Neoniphon (Randall and Heemstra, 1985).
§
adscensionis |
§
marianus |
§
rufus |
§
argenteus |
§
aurolineatus |
§
opercularis |
§
sammara |
§
scythrops |
§
bullisi |
§
caudimaculatum |
§
cornutum |
§
coruscum |
§
diadema |
§
dorsomaculatum |
§
ensiferum |
§
furcatum |
§
hormion |
§
inaequalis |
§
iota |
§
ittodai |
§
lacteoguttatum |
§
lepros |
§
macrosquamis |
§
marisrubri |
§
microstoma |
§
megalops |
§
melanospilos |
§
praslin |
§
punctatissimum |
§
rubrum |
§
shimizui |
§
seychellense |
§
spiniferum |
§
spinosissimum |
§
suborbitalis |
§
tiere |
§
tiereoides |
§
vexillarium |
§
violaceum |
§
wilhelmi |
§
xantherythrum |
|
|
In addition to the above mentioned species,
a complex of five species, Sargocentron inaequalis,
S. iota, S. lepros, S. macrosquamis,
and S. shimizui, is recognized. All are smaller and
possess a distinguishing retrorse spine on the surface of
the nasal bone (except S. shimizui, which lacks this
spine).
In the Wild
Squirrelfish of the genus Sargocentron
can be found throughout the tropical and subtropical waters
of the world. Five species (Sargocentron bullisi, S. coruscum,
S. furcatum, S. lacteoguttatum, and S. vexillarium)
originate from Atlantic waters in the Caribbean; a single
species (Sargocentron suborbitalis) ranging from the
Gulf of California to Ecuador, comes from the Eastern Pacific,
and the remaining 27 species are found in the Indo-Pacific
range. Members of the genus Holocentrus are located
entirely in the Caribbean, while one Neoniphon (N.
scythrops) is located in the Caribbean and the remaining
four are from the Indo-Pacific. The majority of Squirrelfish
are widespread geographically, including S. punctatissimum
and S. tiereoides, which can be found from the east
coast of Africa to Easter Island in the far southeast of the
South Pacific. One species, Sargocentron shimizui,
has the smallest distribution, only being described from Sulawesi.
|
|
Holocentrus adscensionis is rather common in the Caribbean,
from Florida
south to Brazil. They are regularly available within the trade,
and generally can
make a quick transition into the home aquarium. Photos courtesy
of Greg Taylor.
The depth range of this genus ranges from
one or two meters, (S. hormion, S. caudimaculatum, S. cornutum)
to over 180 meters (juvenile S. punctatissimum). However,
the majority of adult Squirrelfish are found shallower than
50 meters. Squirrelfish inhabit both the shallow inshore reefs
and the deep offshore reefs and generally maintain their presence
underneath overhangs. They are almost always found in small
groups, usually consisting of eight to ten individuals.
Typically, upon first seeing a Squirrelfish,
the unusually large eyeball is quickly noted.
Squirrelfish have this large eye because they are primarily
nocturnal and the large eye assists with gathering all available
light, usually moonlight. Specimens can sometimes be seen
during daylight hours, although they will appear reclusive
and will rarely venture out from underneath their overhangs.
The cave or overhang is most often used
both as a shelter and a hiding place. Squirrelfish have few
natural defenses other than staying out of sight from larger
piscivores. Once in view of a predator, squirrelfish will
attempt to use their bony, spiny nature to deter the attack.
All of the dorsal and anal rays are flexed, displaying their
spines, and attempting to appear larger than they truly are.
As a last ditch effort, venom from the spine on their operculum
may be injected into fish that attempt to swallow them.
The diet of squirrelfish is comprised mostly
of crabs and shrimps, though occasionally small fish may be
taken. One study (Hiatt and Strasburg, 1960) investigated
the stomach contents of 13 Sargocentron diadema, revealing
a diet of gastropods, polychaetes, crustaceans (in particular
xanthid crabs), small clams, and a single solenogastre. In
a separate study (Harmelin-Vivien, 1979) 36 of the 76 specimens
collected during the day had an empty stomach. In sharp contrast,
however, only one specimen of the 46 collected in the evening
had an empty stomach.
Squirrelfish have the ability to produce
a multitude of sounds. By contracting muscles, causing vibrations
of their swim bladders, they can create audible sounds that
range from quick cracks and pops to a constant rumble at frequencies
from 75 - 85 Hz (Carlson and Bass, 2000). Interestingly enough,
the swim bladder is not only responsible for vocalization,
but it also assists in their hearing sounds produced by other
squirrelfish. Because there is a tight association between
the rostral end of the swim bladder and the auditory bulla,
the swim bladder functions as a pressure transducer, resulting
in enhanced hearing sensitivity (Carlson and Bass, 2000).
Carlson and Bass hypothesized that squirrelfish are able to
communicate both within and outside of their own species.
Oddly enough, knowledge of the mating
and spawning habits of Squirrelfish is woefully inadequate
for a group found in such large numbers in shallow water.
This is presumably due to their nocturnal nature. It is likely
that mating and spawning occurs entirely after nightfall and
includes all members of the small group. Of the minimal information
available, it appears females are routinely larger than males,
though the difference is often 10mm or less. No other external
differences are readily observable between the two sexes.
Eggs are pelagic, though no one is sure exactly how long they
are free-living. What is known, however, is that juvenile
squirrelfish settle out of the plankton at a size that is
relatively large for a reef fish, sometimes measuring over
one inch of total length.
In the Home Aquarium
Squirrelfish are hardy aquarium fish and
usually make a seamless transition to captive life provided
a few basic needs are satisfied. The first obstacle that must
be overcome is providing them with a suitable habitat. Squirrelfish
will require a fairly decent sized cave or overhang. The larger
your captive group of squirrelfish, the more room that will
be required underneath the ledge. Squirrelfish will spend
the vast majority of their daytime hours below their overhang
or within their cave, patiently waiting for nightfall. With
a little forethought, the hobbyist can set up their display
to both meet this need of the fish, and their own desire for
fish watching.
Squirrelfish are relatively disease resistant
in the home aquarium. Potential problems that may arise are
likely due to the opercular spine. Much like the similar spine
of marine angelfish or the spine near the base of the tail
of the surgeonfish, the spine of squirrelfish has a tendency
to become caught in nets or embedded in the hands of their
caretakers. When caught in nets, the spine may break off or
become damaged. If this occurs, the wound may become a potential
hazard to a bacterial infection, most notably Aeromonas
or Vibrio. The future is not promising for these fish,
and it is best to avoid the purchase of squirrelfish with
damaged operculum spines. However, if this spine becomes embedded
in your hand, special care does need to be taken. As noted
above, some squirrelfish harbor a venom within this spine.
The reaction for humans is reported to be less severe than
similar stings from lionfish or other scorpaenids. However,
seeking out immediate medical attention is still in the aquarist's
best interest, especially if there is a history of known allergies
to insect stings.
The aquarium size for squirrelfish is
not a demanding requirement. Squirrelfish remain fairly inactive
throughout much of their life. They are nearly entirely inactive
during the day, and at night only become active enough to
find food. The main consideration is the size of the fish
- many squirrelfish can reach 12" or larger in an aquarium,
though most remain six to seven inches. In order to house
a small harem or group of squirrelfish, each at 12",
a rather large aquarium will be required. If space is a at
a premium, you may prefer to house only one, or possibly two
or three, squirrelfish or opt for smaller members of the family.
In this instance, a traditional 75 gallon aquarium would be
more than suitable. However, what is more often the deciding
factor for aquarium size is the type of tankmates that are
desired. Squirrelfish, although not threatening to larger
fish, still prefer a peaceful aquarium. If you prefer to house
your squirrel with active swimmers, be sure to increase the
aquarium size accordingly.
Although fairly non-aggressive, squirrelfish
have a propensity to swallow most anything that will fit into
their mouths - fish are no exception. Therefore, any tankmates
must first be considered as potential prey. Any fish that
has the probability to fit into the mouth of squirrelfish
is best left to another aquarium unless the intention is to
offer it as food. For that matter, the aquarist would be wise
to not only include fish in this category but also
any mobile invertebrate. Shrimps, crabs, snails, bristleworms,
and starfish all fit into the profile as potential prey. To
keep this simple, if it walks, crawls, slithers, or swims,
it might be squirrelfish food. It should be obvious at this
point that squirrelfish are not good inhabitants for the traditional
reef aquarium that is typically teaming with small invertebrates.
However, if your goal is to remove invertebrates, such as
bristleworms, from your aquarium, then a squirrelfish may
be a good option.
Compatibility
chart for Holocentrids:
Fish
|
Will Co-Exist
|
May Co-Exist
|
Will Not Co-Exist
|
Notes
|
Angels, Dwarf
|
|
|
X
|
Adult squirrelfish will consume dwarf angels.
|
Angels, Large
|
X
|
|
|
Should be good tank mates.
|
Anthias
|
|
|
X
|
Will be consumed by squirrelfish.
|
Assessors
|
|
|
X
|
Will be consumed by squirrelfish.
|
Basses
|
|
|
X
|
Will be consumed by squirrelfish.
|
Batfish
|
|
X
|
|
Adult squirrelfish can consume juvenile batfish.
|
Blennies
|
|
|
X
|
Will be consumed by squirrelfish.
|
Boxfishes
|
|
X
|
|
Adult squirrelfish can consume juvenile Boxfishes.
|
Butterflies
|
|
X
|
|
Adult squirrelfish can consume juvenile butterflies.
|
Cardinals
|
|
|
X
|
Will be consumed by squirrelfish.
|
Catfish
|
X
|
|
|
Should be good tank mates.
|
Comet
|
|
|
X
|
Will be consumed by squirrelfish.
|
Cowfish
|
|
X
|
|
Adult squirrelfish can consume juvenile cowfish.
|
Damsels
|
|
|
X
|
Will be consumed by squirrelfish.
|
Dottybacks
|
|
|
X
|
Will be consumed by squirrelfish.
|
Dragonets
|
|
X
|
|
The noxious mucous may not be enough to ward off a
hungry squirrelfish.
|
Drums
|
X
|
|
|
Should be good tank mates.
|
Eels
|
|
X
|
|
Some eels require a tank unto themselves.
|
Filefish
|
X
|
|
|
Should be good tank mates.
|
Frogfish
|
X
|
|
|
Should be good tank mates.
|
Goatfish
|
X
|
|
|
Should be good tank mates.
|
Gobies
|
|
|
X
|
Will be consumed by squirrelfish.
|
Grammas
|
|
|
X
|
Will be consumed by squirrelfish.
|
Groupers
|
X
|
|
|
Should be good tank mates.
|
Hamlets
|
X
|
|
|
Should be good tank mates.
|
Hawkfish
|
|
X
|
|
Adult squirrelfish can consume juvenile hawkfish.
|
Jawfish
|
|
|
X
|
Will be consumed by squirrelfish.
|
Lionfish
|
X
|
|
|
Should be good tank mates.
|
Parrotfish
|
X
|
|
|
Should be good tank mates.
|
Pineapple Fish
|
X
|
|
|
Should be good tank mates.
|
Pipefish
|
|
|
X
|
Will be consumed by squirrelfish.
|
Puffers
|
X
|
|
|
Should be good tank mates.
|
Rabbitfish
|
X
|
|
|
Most should mix well, but some Rabbitfish can become
aggressive over time.
|
Sand Perches
|
|
X
|
|
Adult squirrelfish can consume juvenile sand perches.
|
Scorpionfish
|
X
|
|
|
Should be good tank mates.
|
Seahorses
|
|
|
X
|
Will be consumed by squirrelfish.
|
Snappers
|
X
|
|
|
Should be good tank mates.
|
Soapfishes
|
X
|
|
|
Should be good tank mates.
|
Soldierfish
|
|
X
|
|
Some species may not co-exist.
|
Spinecheeks
|
|
X
|
|
Adult squirrelfish can consume juvenile spinecheeks.
|
Squirrelfish
|
|
X
|
|
Some species may not co-exist.
|
Surgeonfish
|
X
|
|
|
Should be good tank mates.
|
Sweetlips
|
X
|
|
|
Should be good tank mates.
|
Tilefish
|
|
|
X
|
Will be consumed by squirrelfish.
|
Toadfish
|
X
|
|
|
Should be good tank mates.
|
Triggerfish
|
X
|
|
|
Should be good tank mates.
|
Waspfish
|
X
|
|
|
Should be good tank mates.
|
Wrasses
|
|
X
|
|
Adult squirrelfish can consume juvenile wrasses.
|
Note: While many of the fish listed
are good tank mates for Holocentrids, you should research
each fish individually before adding it to your aquarium.
Some of the mentioned fish are better left in the ocean or
for advanced aquarists. In addition, for any species listed
as "will co-exist," it is assumed that the fish
is large enough to not be swallowed by the Holocentrid.
It should also be obvious at this point
that squirrelfish are not particularly picky about their prey.
This translates into a fish that is easily fed in the home
aquarium. However, they must be fed a lot of
food. The traditional aquarium favorite of flake or pellet
foods will not sustain a squirrelfish for long. Instead, opt
for pieces of thawed shrimp or fish, or any food geared towards
the diet of large fish such as triggers or puffers. Most squirrelfish
will adapt to consuming food during daylight periods, however
a training period may be required. If the fish is initially
difficult to feed, the aquarist would be best served by offering
live shrimp after nightfall to entice feeding. Once feeding
has commenced on a regular basis, attempt to wean it off the
live food, and finally transitioning it over to a daylight
feeding period.
As noted above, squirrelfish have the ability
to communicate with each other. Be advised
the aqurist
should become accustomed to hearing a multitude of sounds
coming from the aquarium. Undoubtedly, it is their frequent
chirping sounds that have garnered them their common name
not their fluffy tail.
Meet the Species
Possibly the most regularly offered squirrelfish
for the American trade is Holocentrus adscensionis,
or the Big-Eyed Squirrelfish. They are a typical squirrelfish
in all aspects except size - these get very large. They can
reach up to 24" of length. Instead, you may wish to opt
for the Longspine Squirrelfish, Holocentrus rufus,
which is nearly identical to H. adscensionis except
it reaches only 12" in captivity. In addition, the yellow
of the dorsal fin is absent, but instead the yellow highlight
is located on the anal, caudal, and pectoral fins.
The dorsal fin of Holocentrus rufus is seen here on
the left, with the dordal fin of Holocentrus adscensionis
seen on the right. Note the color difference.
Photos courtesy of Greg Taylor.
Neoniphon sammara is a wide-ranging
squirrelfish owning the common name of the Samara Soldierfish,
despite it actually being a squirrelfish. This species is
relatively more outgoing than many of the members of the family.
Typically, it can be seen hovering just outside its preferred
overhang in bright daylight. Preferred territories usually
include overhangs created by thickets of Acropora species.
Over 66% of the diet for this species is crabs, with another
15% attributed to small fish and 10% to shrimp (Randall, 1972).
Neoniphon argenteus is nearly identical. In fact, Beaufort
(1929) incorrectly placed N. argenteus in synonymy
with N. sammara because the two species are so closely
related.
Sargocentron diadema, often called
the Crown Squirrelfish, is the most often offered Indo-Pacific
species. It is generally found in lagoons or bays, not outer
reefs, unlike most of the family. Of all the Sargocentron
species, this is the most likely candidate for venturing out
into bright daylight. Adults may reach nine inches in length.
Conclusion
Squirrelfish definitely fit the bill as
being anything other than a normal, run-of-the-mill fish.
With requirements that are not shining examples of the perfect
reef-aquarium candidate, caution needs to be exercised before
purchasing one. Once the proper setup is established, however,
the addition of a squirrelfish will be a unique addition to
your aquarium.
|