Info

Mollusks

American oyster

Crassostrea virginica

Bay scallop

Aequipecten irradians

Blue mussel

Mytilus edulis

Northern quahog

Mercenaria mercenaria

Pacific oyster

Crassostrea gigas

Southern quahog

Mercenaria campechiensis

Common name

Scientific name

Crustaceans

Blue shrimp Giant river prawn Kuruma shrimp Marron crayfish Pacific white shrimp Red claw crayfish Red swamp crawfish Tiger shrimp White river crawfish White shrimp Yabby crayfish

California giant kelp

Eucheuma

False Irish moss

Gracilaria

Irish moss

Laminaria

Nori or laver

Wakame

Litopenaeus stylirostris Macrobrachium rosenbergii Marsupenaeus japonicus Cherax tenuimanus Litopenaeus vannamei Cherax quadricarinatus Procambarus clarkii Penaeus monodon Procambarus acutus acutus Penaeus setiferus Cherax destructor

Algae (seaweeds)

Macrocystis pyrifera Eucheuma cottoni Gigartina stellata Gracilaria sp. Chondrus crispus Laminaria spp. Porphyra spp. Undaria spp.

cipal groups. Common and scientific names of many of the species of the finfish, mollusks, and crustaceans currently under culture are presented in Table 3. Included are examples of bait, recreational, and food animals.

Various species of carp and other members of the family Cyprinidae lead the world in terms of quantity of animals produced. In 1996, the total was more than 9.6 million metric tons (6). China is the leading carp-producing nation and is the world's leading aquaculture nation overall. Significant amounts of carp are also produced in India and parts of Europe. Species of carp where production exceeded 1 million metric tons in 1996 were silver carp, grass carp, common carp, and bighead carp.

Fish in the family Salmonidae (trout and salmon) are in high demand, with the interest in salmon being greatest in developed nations. Salmon, mostly Atlantic salmon, are produced in Canada, Chile, Norway, New Zealand, Scotland, and the United States. Fish in the family Cichlidae, which includes several cultured species of tilapia, are reared primarily in the tropics, but have been widely introduced throughout both the developed and developing world.

Catfish are not a major contributor to aquaculture production globally, but the channel catfish industry dominates U.S. aquaculture. Catfish production in the United States, primarily channel catfish, was 209,090 metric tons in 1992 (4) and 206,078 metric tons in 1995 (3). Total world catfish production in 1995, which includes walking catfish, was 312,000 metric tons.

Among the invertebrates, most of the world's production is associated with mussels, oysters, shrimp, scallops, and clams. Crawfish culture is of considerable importance in the United States but amounted to only 24,211 metric tons in 1992 (4), insignificant compared with some other invertebrate species. Globally, crawfish production was 29,350 tons, of which more than 28,000 tons was attributable to the red swamp crawfish (3).

Small amounts of crabs, lobsters, and abalone are being cultured in various nations. All three bring good prices in the marketplace but have drawbacks associated with their culture. Lobsters are highly cannibalistic. Rearing them separately to keep them from consuming one another during molting has precluded economic culture in most instances. Spiny lobster (Panulirus spp.) culturists produced a total of 69 metric tons in 1995 (3). Crab culture has also failed to develop in some parts of the world. In the United States, blue crab (Callinectes sapidus) has been attempted but has not been economically feasible, largely due to problems with cannibalism. Global production of crabs in the family Portunidae (of which C. sapidus is a member) during 1995 was only 20 metric tons. Chinese river crabs and various other species of marine crabs are being successfully cultured, with 1995 world production at more than 89,000 metric tons (3).

The dominant mollusks being cultured are oysters, clams, mussels, and to a lesser extent, scallops. Mollusk culture ranges from highly extensive to intensive. An example of one of those extremes is the placement of shell material (cultch) on the substrate (in public waters or a leased site) to provide additional substrate on which naturally produced oyster larvae (spat) can settle. That approach is highly extensive. At the other (intensive) extreme is producing and settling spat in a hatchery and rearing them on strings suspended from rafts or in trays.

Among the mollusks of aquaculture importance, aba-lones eat seaweeds and can only be reared in conjunction with a concurrent seaweed culture facility or in regions where large supplies of suitable seaweeds are available from nature. In some instances the value of the seaweed for direct human consumption may make the highest and best use of the plants.

Well over 100 species of aquatic animals are being cultured primarily for human food. That number expands to several hundred if ornamental, bait, and recreational species produced by aquaculturists are included. Many researchers have turned their attention to species for which there is demand by consumers, but for which the technology required for commercial production is marginal or not completely developed. Examples are dolphin, also known as mahimahi (Coryphaena hippurus), cobia (Rachycentron canadum), red snapper (Lutjanus campechanus), Pacific halibut (Hippoglossus stenolepis), southern flounder (Par-alichthys lethostigma), winter flounder (Pseudopleuronec-tes americanus), American lobster (Homarus americanus), and blue crab (Callinectes sapidus). Each of the species mentioned is marine and has small eggs and larvae. Providing the first feeding stages with acceptable food has been a common problem, as has the fragility of the early life stages of many species, and the problem of cannibalism.

Fish with large eggs, such as trout, salmon, catfish, and tilapia, were among the first to be economically successful in modern times. Small eggs do not necessarily mean that sophisticated research is required to develop the technol ogy required for successful culture. Carp, which have been cultured in China for millennia, have extremely small eggs. At the time the methodology for carp culture was developed, there were no research scientists, although there must have been dedicated farmers who used their common sense and trial-and-error methods to establish aquaculture.

In contrast, relatively large eggs do not necessarily mean that culture will be easy. Fish with very large eggs (eg, such marine catfish as the gaftopsail catfish, Bagre marinus) have eggs well over a centimeter in diameter but such low fecundity that the number of broodstock required to maintain a culture facility would doom the venture. Atlantic and Pacific halibut have eggs of about 3-mm diameter, much smaller than those of trout and salmon, but relatively large relative to many marine species, including other species of flatfish. Halibut eggs are relatively easy to hatch, but the larvae are extremely fragile so providing the nearly static conditions for development without causing water quality degradation is difficult. Nearly one month is required for egg incubation, followed by another approximately 35 days until first feeding, and then several additional weeks before metamorphosis. Following metamorphosis, halibut postlarvae become easy to maintain, but mortality rate from egg to metamorphosis is generally very high.

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