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Fishes assigned to the family Scorpaeonidae
are not limited to the tropics. In fact, they may be relatively
rare there compared to other areas, such as the western coast
of northern North America. In this region 60 to 70 species
of scorpion fishes are found, represented by four genera,
Scorpaena, Scorpaenodes, Sebastes and
Sebastolobus. About 60 to 65 of these species are grouped
in the genus Sebastes, commonly called the "rockfishes"
or "rockcods," whose individuals often comprise
the majority of fishes seen by divers in these areas. The
remaining three genera are represented, in this region, by
one or two species each. A good way to see the relationship
between an average rockfish and a lionfish, for example, is
to take a picture of a lionfish and cover all but about an
inch of the long flowing spines and fin rays. If you do this,
the resulting image will look quite like one of these rockfish.
Rockfish are very economically important
and are the basis of both significant sport and commercial
fisheries, much to their detriment as they are being driven
to extinction in many areas. They are even more important
ecologically, being the dominant fishes in the rock reef communities
that comprise most of that coastal region's environments.
These fish are typical Scorpaeonids in that they possess sharp
spines with venom sacs, but unlike their tropical cousins,
the venom of these cold water forms is only mildly toxic.
Nevertheless, getting "spined" by a rockfish is
still painful, and caution is necessary when handling them.
All of these species have a single dorsal fin with 11 to 17
spines and 8 to 18 rays. The anal fin has three spines and
from five to nine rays. The pelvic fins have one spine and
five rays. Only the dorsal and anal fin spines possess the
venom sacs.
Although the substrate on the exposed North
Pacific coast is often far more brilliantly colored and striking
than coral reef areas, the fishes by and large are not very
colorful. In fact, the area has been referred to by divers
as "The Sea of Brown Fishes." In large part this
is probably due to the richness of the nearshore marine environment
in this area. The planktonic component of the ecosystems is
so great that water clarity is very limited; generally, a
diver or a fish can seldom see more than 20 to 25 feet. In
environments such as these, there is limited utility to colorful
patterns; they simply are not generally visible, and the signals
they would convey in more transparent waters would not get
transmitted. Consequently, the fish are often rather drab.
However, drabness, is not the complete
rule in these areas for many of the rockfishes are brightly
colored, and in fact would be attractive aquarium fish if
it were not for one other attribute not commonly seen in reef
aquarium fishes: their large size. Most coral reef aquarium
fishes are small. The majority do not get over a foot in length.
In the cool waters of the North Pacific, most of the common
fishes exceed a foot in length, and some of the scorpion fishes
may reach lengths of close to three feet. This size, and their
delicious flesh, makes them attractive as food fishes. Nonetheless,
a number of species are quite beautiful animals and do make
attractive aquarium inhabitants in large aquaria.
I don't intend to cover all of the North
Pacific rockfish species in this brief treatment, but I will
concentrate on those few that would do fine in a cold-water
aquarium of at least a few hundred gallons. If you are curious
about some of the others, I have included some links to images
at the end of the article. All of these fish are ovoviparous,
that is their eggs develop internally, and they give birth
to live young. They also, generally, are quite long-lived.
Pacific Ocean Perch, Sebastes alutus, is a commercially
important species that has been well studied and is known
to live more than 30 years, and probably doesn't reach sexual
maturity until it is over 5 years old. The number of fry produced
is "impressive." A small, one foot long, seven year
old, female will deliver about 30,000 offspring, but a larger
female, about 16 inches long, and 20 years old can have over
300,000 offspring. Not surprisingly, the odds of any one of
these tiny fry surviving to adulthood is miniscule.
Many of the other rockfish species are
thought to live as long as Pacific Ocean Perch, but many also
have shorter life spans. In general, they are relatively poorly
known ecologically, surprisingly so when their ecological
and economic interest is considered. Typically, males are
smaller and mature earlier than females. The sexes look alike,
and the only way to tell them apart is during the spawning
season when the females have a decidedly swollen abdomen.
As is usual when several similar species are found together
in nature, the species partition their resource base, be it
food or habitat. In the case of the rockfishes, they seem
to subdivide the habitat; so that individuals of each species
have a characteristic place to live. They all seem to be more
or less opportunistic feeders. If it swims or crawls by and
they can catch it and fit it in their mouths, then it is food.
A Few Good Aquarium Species
Black Rockfish (Sebastes melanops)
Maximum size = 24 inches
In nature, during the day, black rockfish
are pelagic and swim around the outside margins of kelp beds.
They have charcoal grey sides and black mottling along the
back. This species is gregarious and may form quite large
shoals, often containing more than 50 fish. They are predators
on a variety of pelagic organisms, but shrimp make up a large
component of their diets.
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Figure
1. Black rockfish, Sebastes melanops, are
often inquisitive and will sometimes swim very close
to divers.
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Figure
2. The mottled color pattern along the back of the
black rockfish probably helps break up their silhouette
to protect them from larger predatory fish and seals.
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Another image of the black rockfish may
be found by following this link.
Adult and juvenile behavior patterns vary
significantly in this species, and are largely the reverse
of one another. During the day adults are either up in the
water column or, during periods of strong currents, they will
often be found "resting" on rocks or in crevices.
About two hours after dusk they "retire" to their
favorite crack or crevice to spend the night. During the day,
the juveniles are found singly in cracks, crevices, in caves
in the boulder fields, or in the understory kelps in the kelp
forest. During the night these juveniles become more active
and are often found up in the kelp bed.
Copper Rockfish (Sebastes caurinus)
Maximum size = 22 inches
Quillback Rockfish (Sebastes maliger) Maximum size
= 24 inches
These two species, Sebastes caurinus,
the Copper rockfish, and Sebastes maliger, the Quillback
rockfish, are commonly seen in boulder fields or along cliffs,
where they seem to swim a little and rest on the rocks a lot.
When frightened, they tend to swim down into crevices for
cover. These two species may be very difficult to distinguish
from one another. Copper rockfish generally have a
diagonal white stripe on the lateral line on the posterior
part of the body, and their anterior dorsal spines are not
particularly prominent. Quillbacks have enlarged front portions
of their dorsal fins, and they lack the diagonal white lateral
line. They also have similar diets, being predators on small
crustaceans, although they will eat almost any tidbit an exploring
diver turns up. Small Quillbacks are often found living inside
of large glass sponges.
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Figure
3. A juvenile Copper rockfish, Sebastes caurinus,
about 5 inches long, swimming over a rock covered in
vermetid worms and cup corals.
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Figure
4. Adult Copper rockfish, often become very dark,
losing the characteristic copper color of smaller fish.
This individual is about 18 inches long and such large
individuals are rare outside of marine sanctuaries today.
Unfortunately, most of the larger rockfishes are the
larger, more fecund, females. This photo was taken about
20 years ago.
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Other images of Copper rockfish may be
found by following the links located here,
here
and here.
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Figure
5. Rockfish are definitely predatory! If you look
carefully at the mouth of this Quillback rockfish, Sebastes
maliger, you will just be able to make out the tail
of a fish that it ate as I was getting in position to
take the photo.
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Other images of the quillback rockfish
may be found by following the links located here
and here.
Puget Sound Rockfish (Sebastes emphaeus)
Maximum size = 6 inches
The small Puget Sound Rockfish, Sebastes
emphaeus, is often found living along the front of large
caves. These fish tend to be found in small schools of five
to ten fish. As with the Quillback and Copper rockfishes noted
above, it will seek shelter in caves when frightened. This
fish has a beautiful golden color and normally seems to have
little fear of divers or larger animals. Of all the species
discussed in this article, this species is probably the best
candidate for a smaller tank.
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Figure
6. The small Puget Sound Rockfish, Sebastes emphaeus,
is one of the few members of this group of fishes that
is appropriate to small aquaria. This is a mature fish,
and is about 6 inches long.
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China Rockfish (Sebastes nebulosus)
Maximum size = 18 inches
Tiger Rockfish (Sebastes nigracinctus) Maximum size
= 24 inches
The Tiger and China rockfishes are territorial,
cave dwelling fishes, and are amongst the most strikingly
colored of the shallow water Northeastern Pacific rockfishes.
The tiger rockfish, Sebastes nigracinctus, is not,
as one might assume from the name, orange with black stripes,
but rather pink or red with violet or black striping. It is
often very aggressive when defending its "home cave"
and will not hesitate to swim out and threaten an approaching
diver. In an aquarium, this fish is truly striking, but caution
does need to be exercised around its cave, until it has become
used to the aquarist's presence. The China rockfish, Sebastes
nebulosus, is a deep black or bluish color with brilliant
yellow spots mottling the head. Additionally, there is a broad
yellow band running from the third dorsal fin spine down to
the lateral line and thence to the tail. China rockfishes
are also territorial cave dwellers, but they are far less
aggressive than tiger rockfishes. Both the tiger and China
rockfishes may become quite tame, and if a proper cave is
constructed for them, will often come out for hand feeding.
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Figure
7. The large Tiger rockfish, Sebastes nigracinctus,
is one of the more striking fishes in the region. This
female fish is about two feet long, and pregnant. Note
the swollen ventral part of the abdomen; such a female
may deliver over 300,000 fry
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Other images of the Tiger rockfish may
be found by following the links located here,
here
and here.
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Figure
8. This China rockfish, Sebastes nebulosus,
is resting on the rocks outside of its cave. Such fish
are often quite tame, as the next figure shows.
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Figure
9. A different China rockfish from the one in Figure
8, (note the difference in the head coloration) outside
of its cave. Fortunately, most spearfishermen leave
these cave dwelling creatures in peace, as there is
no sport in shooting these animals. Such territorial
fish, however, make ideal aquarium fish and are often
found in public aquaria in this region.
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Other images of the China rockfish may
be found by following the links located here
and here.
Basic Care:
All of these fishes are opportunistic predators,
and this makes feeding them quite easy. They are wholly carnivorous,
but are not too particular about their food. They will eat
just about anything with meat in, or on, it. Many aquarists,
accustomed to the relatively high temperatures of reef aquaria,
tend to think that these animals from colder water have a
lower metabolic rate. This is not the case. Natural selection
has shaped them for their environment and, in terms of calories
per hour, their metabolic rate is as high or higher than their
tropical cousins. These are animals found in waters with a
truly amazing abundance of available pelagic and planktonic
food, and they need to be fed a lot. In nature, mature rockfishes
may eat everything from large drifting plankton, to smaller
rockfishes. To put their food requirements in "reef aquarium
terms," an adult of the larger species could easily eat
the equivalent of several mature, full grown, Amphiprion
clarkii or Lysmata ambionensis shrimp per day;
every day. Smaller individuals would need proportionally less,
but the amount of food is still impressive. The amount of
necessary food makes good filtration a must. For an aquarist
accustomed to the demands of reef aquaria, the filtration
needs of one of these cold water tanks is on the order of
two to four times as much as for a coral reef tank of the
same size. The water temperature needs to be kept between
about 34°F and 50°F; although most of the species
can tolerate short periods, from a few days to a couple of
weeks, where the temperature is as warm as 60°F, prolonged
exposure to such elevated temperatures will kill them. Most
of them, even the sedentary species, need vigorous water movement,
coupled with periods of calm water. Many of the habitats they
are commonly found in have significant tidal currents, and
these fish will do best if the aquarium is set up to mimic
their natural environment. These are, by and large, fish of
rocky reefs, and need a lot of rock work in the tank to provide
appropriate habitats.
Rockfishes are long-lived animals with
specific habitat needs, and the aquarist should attempt to
accommodate them in tanks that mimic their natural habitats.
Black rockfish do well in deep wide tanks with rock work at
one side and a lot of open space. Although it is often impossible
to provide a mimic for the kelp they normally swim around,
this doesn't seem to be a drawback to their survival in a
tank. Crevices need to be provided in the rockwork for their
nocturnal sheltering. Copper and Quillback rockfishes do well
in a tank with a lot of rock work, including a lot of crevices
and small caves. They really don't need much in the way of
open water space. China and Tiger rockfishes need a well-defined,
relatively small, cave; generally, this cave should be about
two to three times the height and width of the body, and about
two body lengths deep. They will take up "sitting"
stations within their caves, and leave them only to dash out
for food. Puget Sound rockfishes need a larger cave, two to
three feet in diameter, and about the same in depth, and they
will shoal in its mouth.
In nature many of these speciesare being
driven to local extinction by over fishing, not only from
commercial fishermen, but also from sport fishermen and divers.
In some of the areas in the Puget Sound region, the larger
female Copper rockfishes are now completely absent from the
populations, most likely extirpated by spear fishing. These
larger females were, of course, the source for most of the
eggs produced in their populations. There is some hope that
these populations may recover, particularly in areas of marine
reserves, but it is really too early to tell. Since these
fish will all live for decades under the right conditions,
it is imperative that any kept by hobbyists, be treated with
the respect and care that befits a long-lived animal.
Images of some other Pacific Coast rockfishes
will be found at these links:
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