Cod

Cod are fish of the genus Gadus (family Gadidae, order Gadiformes, class Osteichthyes). The genus Gadus includes from one to five species, depending on which are counted as full species. The type species of the genus is Atlantic cod Gadus morhua. Other species are the Pacific cod, G. macrocephalus, and the Greenland cod, G. ogac, earlier thought to be subspecies of the Atlantic cod but recognized currently as full species. Baltic cod and White Sea cod are regarded as subspecies of the Atlantic cod at present but they differ enough to be recognized as full species.

Cod is also used as a common name of some groups of fishes, mainly belonging to the gadids, but also other families: Antarctic rock cod (Nototheniidae, Perciformes), Arctic (polar) cod (genus Boreogadus saida and Arctogadus glacialis, both Gadidae), blue cod (Paragercichthys, Mugiloididae, Perciformes), blue rock cod (Indonotothenia, Nototheniidae), cultus cod (Hexagrammidae, Scorpaeniformes), deep-sea cod (Moridae, Gadiformes), eucla cod (Euclichthyidae, Gadiformes and Euclichthys), gray rock cod (Lepidonotothen, Nototheniidae), grenadier cod (Tripterophycis, Moridae), moray cod (Muraenolepididae, Gadiformes), morid cod (Mora, Moridae), murray cod (Macculochella, Serranidae, Perciformes), rock cod (Epinephelus, Serranidae), southern rock cod (Nototheniidae), and toothed cod (Arctogadus, Gadidae and A. borisovi).

Cod have three dorsal and two anal fins. The caudal fin is truncated or square. The upper jaw projects beyond the lower jaw. A barbel (whisker) on the chin is about as long as the eye diameter. The lateral line is light in color, with a slight curve above the pectoral fin. Color is usually greenish-brown with small dark blotches. Morphologically, the different cod species can be distinguished by differences in structure of the swim bladder anterior extension, interorbital width (least width between the eyes) and other ratios, and shape of the scale tubercles (small knobs projecting from the scales).

Fish of the genus Gadus are distributed in cool-temperate to Subarctic areas of the North Atlantic and North Pacific oceans and adjacent Arctic Ocean. All cod are bentho-pelagic, adapted to feed mainly near the sea bottom, and for catching prey on and below the bottom surface. Cod are omnivorous, eating plankton and other fish. Cod capture prey mainly by suction, but are also well adapted for seizing and biting and can swallow large and heavily spined prey. The chin barbel and extended pelvic fin rays, equipped with sensory cells, are used to locate food in the bottom substrate.

Atlantic Cod

The Atlantic cod Gadus morhua is one of the most economically important fish in the world. They inhabit the northern part of the Atlantic Ocean and adjacent Arctic areas, and are distributed in the western North Atlantic from Baffin Island and Newfoundland southward along the continental slope to the Gulf of Maine, rarely to Cape Hatteras, and even to Cape Lookout, North Carolina, at latitude 34°34' N. They occur in the waters off Greenland, Iceland, and the Faroes, and in the eastern North Atlantic from the Bay of Biscay north and eastward to Spitsbergen and Novaya Zemlya, entering the White Sea; also in the western part of the Baltic Sea (eastward to Bornholm Island). In warm years Atlantic cod enter the Kara Sea in small numbers. The northernmost record is at latitude 81°52' N. In some regions they occur sympatrically with the Greenland, Baltic, White Sea cods. The southern limit of distribution coincides usually with surface isotherm 10°C in winter. The northern limit is related to penetration of comparatively warm Atlantic waters into the Arctic.

Arctic (polar) cod, Resolute Bay, Nunavut. Copyright David R. Gray

Atlantic cod have many small spots on the body except the head and fins. They inhabit waters from inshore regions to the edge of the continental shelf at depths up to 500-600 m, more often from 180 to 300 m. Although they are adapted for bottom life, they may also spend much time off the bottom. Cool temperatures are preferred, generally in the range of -0.5°C to 10°C.

Cod tend to move in schools, and undertake migrations. In some areas they move offshore in winter and inshore in summer. In other areas regular migrations from feeding areas to spawning grounds are about 1500 km long. The greatest recorded distance traveled by tagged cod was about 3300 km: from the central North Sea to the Grand Bank of Newfoundland.

Cod are voracious feeders and their feeding habits may influence significantly the size of cod populations through cannibalism, and also the size of populations of other fishes such as redfish, capelin, and sand lance. As fry, cod feed on a variety of small creatures such as copepods, amphipods, and barnacle larvae. Juveniles and young adults continue to eat crustaceans such as euphausiids, mysids, shrimps, small lobsters, spider crabs, and hermit crabs. When about 50 cm long, fish become the predominant food. Depending on locality and availability, capelin, sand lance, redfish, and herring are important foods. But many other species of fishes are also eaten, including alewives, Atlantic and Arctic cod, cunner, flounders, haddock, hake, mackerel, shannies, snakeblenny, sculpin, and silversides. Squid, banks clam, mussels, and nudibranchs are also eaten. Cod also eat many other creatures such as tuni-cates, comb jellies, brittle stars, sand dollars, sea cucumbers, and marine worms; fish offal, including fish heads and entrails from fishing boats; and even occasionally seabirds.

During courtship, the male makes a flaunting display of its median fins and produces grunting noises. It approaches the female from below or one side, presses the lower jaw onto the back of the female, and, pushing her downwards, swims onto her back. Once the male has mounted dorsally he immediately slips down one side of the female, still with the ventral surfaces of both fish and their genital apertures closely pressed together. Subsequently the fish spawn. The dorsal mount appears to be an essential forerunner of the ventral mount.

Young cod fall prey to a number of predators such as older, larger cod, squid, and pollock. Larger cod are in turn eaten by marine mammals, particularly harbor, gray, and harp seals. Pilot whales prefer squid but eat cod in the absence of squid.

In each of the different regions there are one or more identifiable cod stocks or populations, and the life cycle of each is related to the system of local ocean currents. The most important stocks are in (1) the Norwegian and Barents seas (spawn at the north Norwegian coast, feeding grounds in the Barents Sea and in Spitsbergen/Bear Island shelf waters), (2) Iceland waters (connected with the Irminger current, spawn near the south and southwest coast of Iceland, make feeding migrations to northern Iceland and in Greenland waters), (3) Greenland waters, (4) Labrador waters (connected with the circulation of warm Atlantic waters penetrating into the Davis Strait, spawn near northern Labrador; fry drift to the northwestern Newfoundland area), and (5) Newfoundland waters (connected with the frontal zone of Gulf

Stream from Cape Cod to the Great Newfoundland Bank). Smaller stocks also exist in the North Sea, near the Faroes, Ireland, Scotland, in the English Channel, and in the western Baltic Sea.

The Arcto-Norwegian (Lofoten-Barents Sea) stock of the Atlantic cod is the most numerous and widespread. The usual length is 40-80 cm, the maximum length is 180 cm, and weight is up to 40 kg; known age is up to 25 years, but usually not more than 15 years. They attain sexual maturity usually at 6-10 years and at a length of 65-100 cm, but partly at age 3 or 4 years and lesser than 50 cm long or at 12-14 years. The main spawning grounds lie in northwest Norway (West Fjord and near the Lofoten Islands). They spawn in bays and above coastal banks at a depth of about 100 m, from February to May, mainly in March-April, at water temperatures of 4-6°C, and a salinity of about 34%o. In some years spawning also takes place near Bear Island and on the west Murman coast, with a center in Motovsky Bay in the Barents Sea. The spawning period of each female is about 2 months, during which it lays from two to eight clutches of eggs, each egg 1.2-1.5 mm in diameter. The number of eggs produced, correlating with age and length, varies from 170 thousand to 18 million. Pelagic eggs float up in the upper layer and drift with currents, partly in the direction of Bear Island, but mainly into the Barents Sea. During drifting migration the young feed by small plankton organisms. In June, the young of 3-4 cm length drifting northward reach 72-73° N, and drifting eastward reach about 33-34° E. In September, the young reach eastern and northern limits of the Barents Sea (western coast of Novaya Zemlya and Spitsbergen northward to 80-81° N), and descend to the bottom.

During the first 2 years, young cod in the Barents Sea do not undertake large migrations; they are adapted to low temperature (about 0°C) and feed mainly on small crustaceans. From 3 years, the cod start feeding migrations: in summer on stream north- and eastward, and in winter against stream south- and westward. The extent of migrations enlarges continuously. The cod start to eat fish and grow faster: at age 3 years the weight is about 300-500 g, at age 4 about 600-700 g, and at age 5 about 1000-1200 g. Food includes animals of more than 200 species and consists mainly of capelin, herring, polar cod, young cod, molluscs, and crustaceans. Differences in food content are known, related to age, season, and locality. From, on average, age 8-10 years and weight 3-4 kg, the cod start to undertake spawning migrations. In summer, they use rich feeding grounds at the eastern and northern parts of the Barents Sea, and in September-October they form large schools and start to move to the Lofoten Islands, orientating in branches of the Nord-Cap current. A distance of about 1500 km takes 5-6 months, at an average speed of 7-8 km per day.

Coastal cod may be distinguished from this oceanic population. Coastal cod are known from the Norwegian and Barents Sea coast. In spite of simultaneous spawning in the same areas, the two groups of cod have significant differences in the shape and structure of otoliths (the calcareous concretion in the inner ear, which shows an annular growth pattern), as also in the frequency of some hemoglobin alleles, and of blood types. Coastal cod have a smaller number of vertebrae, faster growth, and reach sexual maturity at a younger age; the weight at the same length is higher. The body shape of oceanic cod is more slender than that of coastal cod. The latter prefer the shallow waters at the coast, while the Arctic cod prefer the open sea and deeper waters both offshore and inshore.

In the Barents Sea region, the cod total catch comprised 39.4 million tons from 1946 to 1999, and the average annual catch comprised 729.6 thousand tons (ranging between 240 and 1397.1 thousand tons). Since the 1970s, the stock has been in a depressive state.

The Iceland-Greenland stock of Atlantic cod has a wide feeding area and local spawning grounds. Iceland cod spawn off the south and southwest coast of Iceland from March to May with a peak at the end of April, at temperatures of 5-7°C and a salinity of 32-35%o. The incubation time is 3-5 weeks. Eggs and larvae drift in Irminger current northward: to northwest, north, and northeast coastal Iceland waters, where they feed and grow. In some years a significant number of the young (about 8-25%) drifted to the Greenland shelf, returning back as adults to spawn in Iceland waters. Catches of cod in Iceland waters comprised 300-400,000 tons, and have declined since the 1990s.

The Greenland stock of Atlantic cod inhabits southern Greenland waters, on the west coast northward to about 70° N (region of Disko Island) and on the east coast to 65°35' N (Ammassalik). They are distributed from inshore waters to about 600 m depth, usually above the continental shelf, occurring both on the bottom and some 50-80 m off the bottom. Fish migrate to deeper waters in summer. Tagging experiments have indicated that some mature cod migrate from West Greenland to East Greenland, with some moving as far as Iceland.

The minimum average body length occurs in northern West Greenland, the length increasing from southern West Greenland to East Greenland. Growth varies considerably according to stock condition, locations, and other factors.

On the eastern coast, cod spawn from 63°30' N southward to Kap Farvel, at a depth of 200-400 m at bottom temperatures of 2.5-4.5°C. Main spawning grounds lie in Ammassalik area, where a peak of spawning takes place in April to the beginning of May. On the western coast, cod spawn in open offshore waters northward to 63° N, and then in fjords northward to 67° N. Spawning takes place here at the end of March, with a peak in April, and ends in June, at a depth 50-550 m, at bottom temperatures of 1.5-3.5°C. Incubation time varies from 50 to 17 days at temperatures of -0.6°C to +5.0°C.

The Greenland stock of Atlantic cod was especially numerous in the 1820s and 1840s. Then cod stocks migrated and fishery greatly decreased. Another peak of high cod catches was in the 1920s-1970s. During 1961-1968, the total annual catch off West Greenland varied between 350 and 450,000 tons. Catches decreased to 6600 tons in 1986, but recovered to 110,000 tons in 1989. The estimated biomasses were 21-88,000 tons off East Greenland during 1980-1985 and 25-180,000 tons off West Greenland during 1982-1985.

In the western North Atlantic, at least 12-14 stocks are recognized: southern Labrador-east Newfoundland stock, northern Labrador stock, west and east Scotian shelf stocks, the northern and southern Gulf of St Lawrence stocks, southern Grand Bank stock, Banquereau-Sable Island stock, St Pierre Bank stock, Georges Bank stock, and others. Over the entire Canadian Atlantic region, spawning begins in the north in February and ends in December. Cod spawn over a wide area on the continental shelf, but the area involved is so large and the conditions so varied that generalization would be misleading.

The number of eggs produced increases with the size of the female: from 200 thousand to 12 million eggs. The eggs are pelagic, 1.2-1.6 mm in diameter. Incubation time varies from 50 to 60 days at surface temperatures of -1.5°C to 0°C, to 14 days at a temperature of 6°C. At hatching, embryos are 3.3-5.7 mm long. The young remain pelagic until they reach a length of 30-50 mm, when they descend to the bottom. Growth rates vary with stock and locality. In general, growth is slower (and fish live longer) off Labrador and eastern Newfoundland than on southern Grand Bank, and slower in the Gulf of St Lawrence than on the Scotian shelf. On average, 10-year-old cod from inshore Labrador measure 57 cm long, from the southwestern Gulf of St Lawrence 70.8 cm long, and from Grand Bank about 86.5 cm long. The average age of cod caught by commercial fishery in the 1970s was younger than in the 1950s—that is, the average age declined. Cod older than 20 years are rare; the maximum age is regarded as 29. The all-tackle world record is 44.79 kg for a cod caught off New Hampshire in 1969. The largest weight ever reported was 95.9 kg for cod from a line trawl off Massachusetts in 1895.

Atlantic cod continue to be Canada's single most important commercial species in terms of landed value. Canadian fishermen capture 70-75% of all fish caught in the northwest Atlantic, where at least 13 countries engage in fishery. In 1983, Canada landed 509,052 tons, and in 1984, 463,100 tons. Major fishing grounds are on the continental shelf off Labrador and off eastern Newfoundland and include the Grand Bank and northern Gulf of St Lawrence.

Atlantic cod have been pursued on the fishing banks of the North Atlantic for centuries. Prior to the 1970s, the annual catch was 2.6-4 million tons, taking third place in the world fishery (after Peruvian anchovy and Atlantic herring), and gave 5-6% of the world catch. The stock decreased after 1975 and is in a depressive state until now. Cod stocks have been overfished in some areas (Atlantic Canada) and are at dangerously low levels in parts of the North Atlantic and North Sea. Atlantic cod are caught commercially by otter trawls, pair trawls, line trawls, Danish seines, handlines, jiggers, traps, and gill nets. The delicious flesh is used fresh, frozen, smoked, salted, and canned. Special parts such as cod cheeks and cod tongues are considered delicacies by many maritime peoples. Additional by-products include fish meal, cod-liver oil rich in vitamins A and D, and glue. Eggs are commercially used in Norway.

Kildin Cod

The Kildin cod Gadus morhua kildinensis is a relict population of the Arctic cod, known from Lake Mogilnoe on Kildin Island, a small island in the Barents Sea near the Kola Fjord entrance. Earlier the lake was a sea bay; now it is isolated, c.500 m long, 17.5 m deep, with the upper 5 m layer being fresh water and the bottom layer (below 12-13 m) saturated by hydrogen sulfide. These cod live in intermediate salt water usually at salinities of 15-32%«, but also occur in the fresh upper layer. Their color is very spotted, including the head, dorsal, and caudal fins. The body length is up to 60-80 cm. Kildin cod spawn in February to March, and feed on crustaceans. Kildin cod are poorly studied; their population is not numerous and they may be endangered. They are included in the Red Book of the Russian Federation, which lists endangered wildlife species.

Baltic Cod

The Baltic cod Gadus morhua callarias or Gadus callarias is adapted to live in sea water with a low salinity, and is one of the most important commercial fishes in the Baltic Sea. Whereas the Atlantic cod G. morhua morhua inhabits western parts of the Baltic

Sea, the Baltic cod occurs in the eastern part of the sea eastward of Bornholm Island: northward distributed to about 63° N, escaping freshened waters of Bothnian Bay and Finland Gulf.

Baltic cod differ from Atlantic cod in the shape of the swim bladder anterior extensions, which are very long and rolled at the tips; they also differ in biochemical and genetic characters, life cycle, spawning regions, and migrations. The maximum length is usually 40-45 cm, and the known maximum age is 10 years. They attain sexual maturity at the age of 3 years at a length of 20-27 cm. Baltic cod spawn mainly in Bornholm, Gdansk, and Gotland basins from March to August with a peak in May-June. Spawning occurs at a depth of 80-100 m, in waters with salinity not less than 10%c (usually 12-18%o), at temperatures of 4-5°C. Eggs are pelagic, 1.5-2.0 mm in diameter. During the first two years, the young feed mainly on crustaceans and worms (polychaetes), and later on fishes (Baltic herring, sprat, and others).

From the end of the 1970s to the beginning of the 1980s, the total catch of both Atlantic and Baltic forms of cod in the Baltic Sea was 500-700,000 tons, and later decreased to less than 100,000 tons.

White Sea Cod

The White Sea cod Gadus marisalbi inhabits most saline waters of the White Sea and usually does not occur in the freshwater Dvina, Mezen', and Onega bays. Its color is usually a uniform dark olive-brown. The maximum length is usually 20-40 cm, rarely 58-60 cm, and the age is up to 12 years. In commercial catches, 3-5-year classes predominated, with lengths of 25-35 cm. They attain sexual maturity at 2-4 years.

White Sea cod spawn under ice, at temperatures of -0.5°C to -1.5°C, from the end of February to the end of May, with a peak in March-April. They spawn in coastal zones at a depth of 9-20 m, and in inlets and straits above 10-100 m. They produce from 60 to 350,000 pelagic eggs. Incubation time varies from 35-40 to 12-13 days. On spawning grounds, the maximum number of eggs in the upper 1 m layer occurs usually in April-May, and the maximum number of larvae occurs in May-June. Planktonic young of length 3-4 cm are hatched in July.

Adults in summer occur inshore, and in autumn migrate to wintering grounds, which are not far from the spawning grounds. In spring, after breeding they migrate to feeding areas. Young fish prefer depths of 3-12 m.

Young fish feed on crustaceans (mysids, gam-marids); adults eat fishes (sand-eel, capelin, herring, cottids, small cods) and invertebrates (mainly molluscs and worms). They feed intensively in shallow coastal waters from June to September. The White Sea cod is of local commercial importance, comprising 4-5% of the annual fish catch in the White Sea.

Greenland Cod

The Greenland cod Gadus ogac is more similar to the Pacific cod than to the Atlantic cod. They occur from Alaska (west to Pt Barrow), along the Canadian Arctic coast and archipelago, to West Greenland (from Kap Farvel to Upernavik, 72°55' N), southward into Hudson Bay. They also occur in the Canadian Atlantic region from Ungava Bay and Hudson Strait, southward along the Labrador coast to Newfoundland, and are numerous in the Gulf of St Lawrence, southward to Bras d'Or Lake and Cape Breton, Nova Scotia. They inhabit cold temperate to Arctic waters, and are the most common cod in harbors and fjords, occurring less commonly in offshore waters. In the Hamilton Inlet and Lake Mellville region in Labrador, it is an estuarine species. They produced a lake population in Lake Ogac (Baffin Land, near the corner of Frobisher Bay), which is numerous and used by indigenous people. They also occur in Miramichi estuary and in Brass d'Or Lake. Greenland cod inhabit waters to a depth of 400 m.

The body is brown dorsally and laterally, and white ventrally. This species differs from G. morhua in its darker coloration, it lacks distinct spots, has wider interorbital width, and has larger-scale tubercles (c.8.2% of scale length), which are easily visible with the unaided eye, detectable by touch, and club-shaped.

Spawning occurs along Greenland shores in February and March. About 1-2 million eggs are produced. Eggs are pelagic. The young attain sexual maturity at 3 or 4 years at a length of about 70 cm. The maximum age is 11 years; also more commonly they attain an age of 8-10 years. They eat mainly fishes, especially capelin, polar cod, smaller Greenland cod, and Greenland halibut; among the invertebrates, amphipods, shrimps, crabs, molluscs, and polychaete worms are commonly eaten. The species is of minor commercial importance.

Pacific (Alaska) Cod

The Pacific cod Gadus macrocephalus inhabits the northern part of the Pacific Ocean, from the Bering Strait to the Yellow Sea along the Asian coast and to Oregon along the American coast. The body length is up to 90 (rarely 100-120) cm.

In the western North Pacific, at least ten local stocks exist. The stock of the Anadyr-Navarin region is the largest. In commercial catch, fishes of 32-74 cm length occur; 82.8% are 40-65 cm long and weight is 350-5950 g. Females are larger than males.

Pacific cod occur at temperatures of -1.5°C to 18°C, an optimum of 2-8°C in summer and of -0.5°C to 5°C in winter. In northern regions, Pacific cod spawn at temperatures of 0-3°C at a depth of 200-300 m. In the Anadyr Bay they spawn in April-May, and in southeastern and eastern Kamchatka in February-March. Eggs are adhesive, demersal, that is, sinking to or deposited near the sea bottom (in contrast to all other cod species), and small (0.95-1.11 mm in diameter). Hatching embryos are 3-3.5 mm. Migrations usually are not prolonged: in summer inshore (to depths of 30-60 m) and in winter offshore.

The total catch of Pacific cod comprised about 15-20 million tons. In the western North Pacific, the stock of the Anadyr-Navarin region yields about a half of the total annual catch of cod. In 1995-1996, the commercial stock of cod in the Anadyr Bay was estimated as 190 thousand tons.

Natalia Chernova

See also Cod Wars; Fish Further Reading

Andriashev, Anatoly Petrovich, Fishes of the Northern Seas of USSR, Moskva-Leningrad: Izdatel'stvo Akademii Nauk SSSR, 1954

Bakkala, Richard G., "Pacific Cod of the eastern Bering Sea." Bulletin of International North Pacific Fishery Commission, 42 (1984): 157-179 Campbell, Jone S. (editor), Symposium on the Biology and Ecology of Northwest Atlantic Cod (1994; St John's Newfoundland). Selected Proceedings of the Symposium on the Biology and Ecology of Northwest Atlantic Cod, St John's Newfoundland, October 24-28, 1994, Ottawa (Canadian Journal of Fisheries and Aquatic Sciences, 54(Supplement I) (1997)) Hannesson, R., Fisheries Mismanagement: The Case of the North Atlantic Cod, Oxford: Fishing News Books, Blackwell Science Ltd., 1996 Horsted, Svend Aage, "A review of the cod fisheries at Greenland, 1910-1995." Journal of Northwest Atlantic Fisheries Science (special issue), 28 (2000): 1-121 Jakobsson, Jakob (editor), Cod and Climate Change: Proceedings of a Symposium held in Reykjavik, August 23-27, 1993, Copenhagen: International Council for the Exploration of the Sea, 1994 (ICES Marine Science Symposia, 198, 1994) Jonsson, Jon, Tagging of Cod (Gadus morhua) in Icelandic waters, 1948-1986; Tagging of Haddock (Gadus aeglefinus) in Icelandic Waters, 1953-1965, Reykjavik: Hafrannsoknastofnunin, 1996 J0rgensen, Terje, "Long-term changes in age at sexual maturity of Northeast Atlantic cod (Gadus morhua L.)." Journal du Conseil, 46(3) (1990): 235-248 Kurlansky, Mark, Cod: A Biography of the Fish That Changed the World, New York: Walker, 1997 Matishov, Gennady G. & Alexey V. Rodin (editors), Atlantic Cod: Biology, Ecology, Fishery, St Petersburg: Nauka, 1996 (in Russian with contents and summary in English) Morin, Bernard, Christiane Hudon & Friderick Whoriskey, "Seasonal distribution, abundance, and life-history traits of Greenland cod, Gadus ogac, at Wemindji, eastern James Bay." Canadian Journal of Zoology, 69 (1991): 3061-3070

Smirnova, Natalia Fedorovna & Nikolay Pavlovich Smirnov, Atlantic Cod and Climate, St Petersburg: Rossiysky Gosudarstvenniy Gidrometeorologicheskiy Universitet, 2000 (in Russian) Svetovidov, Anatoliy Nikolaevich, Gadiformes (Treskoo-braznye), translated from Russian, Jerusalem, Published for the National Science Foundation, Washington, D.C. by the Israel Program for Scientific Translations, 1962 -, "Gadidae." In Check-List of the Fishes of the NorthEastern Atlantic and of the Mediterranean, edited by Jean-Claud Hureau & Theodor Monod, Paris: UNESCO, 1973 Vladykov, Vadim D., Claude B. Rennauld & Sylvie Labramboise, "Breeding tubercles in three species of Gadus (cods)." Canadian Journal of Fisheries and Aquatic Sciences, 42 (1985): 608-615

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