Coldwater Scorpaenids - The Rockfishes of the Northeastern Pacific
| 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.
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 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.
Other images of Copper rockfish may be found by following the links located here, here and here.
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.
China Rockfish (Sebastes nebulosus) Maximum size = 18 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.
Other images of the Tiger rockfish may be found by following the links located here, here and here.
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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Useful References:
Eschmayer, W. N., E. S. Herald, and H. Hammann. 1983. A field guide to Pacific Coast fishes of North America from the Gulf of Alaska to Baja California. Houghton Mifflin Company. Boston. 336 pp.
Gotschall, D. W. 1989. Pacific Coast inshore fishes. Sea Challengers. Monterey, California. 96 pp.
Hart, J. L. 1973. Pacific fishes of Canada. Fisheries Research Board of Canada. Bulletin 180. 740 pp.
Lamb, A. and P. Edgell. 1986. Coastal Fishes of the Pacific Northwest. Harbour Publishing. Madeira Park, B. C., Canada. 224 pp.
Moulton, L. L. 1977. An ecological analysis of fishes inhabiting the rocky nearshore regions of northern Puget Sound, Washington: UW; 1977 Ph.D. Dissertation. (Fisheries). 194 pp.from : http://reefkeeping.com/issues/2002-11/rs/index.php
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