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Developmental Species |  Atlantic Salmon |  Freshwater Baitfish
Oysters |  Mussels |  Clams |  Scallops

Developmental Species

cod halibut
With the decline in wild groundfish populations, there is considerable interest in developing efficient techniques for raising cod, halibut, and haddock on fish farms. Researchers at the University of Maine are studying both the nutritional needs of larval cod and haddock and the type of food needed to maximize healthy growth in the early stages of these fish. The University of Maine's Center for Cooperative Aquaculture Research is experimenting with different ways of hatching and raising haddock and halibut on a commercial scale.

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Atlantic Salmon

Maine aquaculturists have been raising salmon since the 1970s. Hatcheries throughout the state (some as far inland as Bingham and Frenchville) produce 3- 1/2 million fish each year for net-pen operations along the coast.

The Atlantic salmon is an anadromous species, spending part of its time in fresh water and part in salt water. In the wild, most of an adult salmon's life is spent in the ocean. During the spring of the fourth or fifth year, the adult fish will return to its river of origin to spawn. After about two or three years in fresh water, young fish will go through a physiological change known as smoltification, which makes the fish ready for life in the sea.

The steelhead trout, also called salmon trout and sea run rainbow trout, belongs to the same family (the salmonids) as the Atlantic salmon. The steelhead has been referred to as the saltwater version of the rainbow trout. The life cycle of the steelhead is essentially the same as the Atlantic salmon, except the steelhead does not go through true smoltification. Like the salmon in the wild, the steelhead returns to fresh water to spawn. Both species have pink or red flesh. The steelhead also looks like the Atlantic salmon, but is likely to have on its flanks an iridescent sheen that flashes red and green; hence the name "rainbow." When the steelhead returns to fresh water to spawn, the rainbow markings intensify.

The steelhead has been domesticated for 150 years, much longer than the Atlantic salmon. The optimal temperature range for the steelhead is higher than for the Atlantic salmon, but since the life cycles of the two species of fish are so similar, producers often grow them together.

In salmonid farms, some adult, four-year-old fish are reserved for broodstock. Spawning occurs between mid-November and mid-December. A 12- pound female fish produces an average of 10,000 eggs each season, which are fertilized and then incubated at a freshwater hatchery. The eggs hatch and eventually grow into free-swimming fry. When fry develop dark vertical bands on their sides during the first year of life, they are called parr. For the first 18 months of their life cycle in the hatchery, parr are graded, vaccinated against diseases, and their health and growth monitored. After 2-3 years in fresh water, young salmon undergo major changes that enable them to live in salt water. Their kidneys adapt to excrete salt, rather than retain it. Their skin becomes silvery so the fish will be less visible to predators in the ocean. Changes also occur in the eyes, blood plasma, musculature, and fat. This process is called smoltification. The smolts, roughly five inches long, are transferred to floating pens in the sea, typically between mid-April and mid-May.

Net pens are generally 20 feet deep, and large pen systems, held in place with moorings, may cover several acres of surface water. In the pens, fish are fed pellets of fish meal, vitamins, and minerals. To prevent the spread of disease, fish are inoculated or antibiotics added to the fish feed. During about two years in the pens, fish grow from smolts weighing3-5 oz. (80-120 grams) to fish with a market weight of 6-12 pounds. A farming operation with 2-1/2 acres of net pens can produce about 50,000 fish each year for market.

When they reach marketable size, the fish are harvested, cleaned, iced, and shipped to customers. Because salmon and steelhead can be harvested on demand, a good selling point for farm-raised fish is prompt delivery of a fresh product.

Seven commercial freshwater hatcheries in Maine produced about 3 million young salmon and 100,000 steelhead in 1995. There are 28 saltwater (grow-out) sites, located primarily in Washington and Hancock counties, where excellent water quality, protected bays, water temperatures of 0-15C ( 32- 59F), strong currents, and high tides provide ideal conditions for raising salmon. In 1998, fish farming generated more than $65 million in gross sales revenue, and the salmonid aquaculture industry has brought much needed aid to economically depressed communities. Increasingly, fishermen who depend on wild fish stocks for their livelihood are considering putting their skills to work in aquaculture to supplement their incomes.

Another economic benefit of salmon and steelhead trout farming is the increase in the number of family-owned smoke houses, where the fish are processed for a gourmet market. An inexpensive and nearby supply of high quality fish makes these spin-off cottage industries possible. Furthermore, a health-conscious public creates a demand for salmon and steelhead, which are excellent sources of protein, omega-3 fatty acids, and vitamins A,B, D, and E. These fish species are also low in sodium, rich in potassium, and are natural sources of selenium, iodine, and fluorine.

In addition, the bio-technology industry may benefit from salmonid farming. Serum from fish blood, one of the by-products of harvesting salmon and steelhead trout, can be used by scientists in bio-medical research and may offer advantages to researchers over the more commonly used mammalian serum. A way to extract large quantities of uncontaminated fish serum for use in laboratories is currently being developed.

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Freshwater Baitfish

Small freshwater fish are commonly used as bait while fishing for sport fishes in Maine, especially in winter. Aquaculture of small fish, especially golden shiner (Notemigonus crysoleucas), is extremely big business in other parts of the U.S., eg. Arkansas. It is not legal to import live baitfish into Maine, therefore, there is a captive market and a large demand for baitfish which originate within the state. Much of this demand is now being met by the capture, storage, distribution, and sale of wild fish. Wild stocks are limited and cannot be relied upon for satisfying demand throughout the season.

Several species of small fish are legal for use as bait but four species dominate sales: golden shiner, common shiner (Luxilus cornutus), fathead minnow (Pimephales promelas), and rainbow smelt (Osmerus mordax).

Due to our short growing season it is challenging to rear baitfish to market size in one season in Maine. However, several Maine people are successfully rearing golden shiners and fathead minnows in pond aquaculture sites. Smelt have not yet been reared in commercially viable numbers. Because of their high retail value ($3.00 to $12.00/dozen) successful smelt culture could be very profitable but many biological and technical obstacles exist which must be overcome before smelt culture becomes a reality.

The majority of baitfish sales in Maine are during the three month ice fishing season. Total sales exceed $5 million and each year demand exceeds supply. Average price varies regionally and seasonally within the state but averages about $2.50/ dozen for minnows and $5.00/dozen for smelt.

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In the 1970s, companies in Blue Hill and on the Damariscotta River pioneered oyster aquaculture in Maine using rafts to culture European oysters (Ostrea edulis). Hatchery-produced seed oysters were reared to market size in Japanese lantern nets, stacked trays, or floating trays suspended in the water. Suspension culture, in which oysters or mussels are grown off bottom, in floating trays and on ropes, is a labor-intensive form of cultivation that requires continuous tending and cleaning of both gear and shellfish. On the US East Coast, where the bulk of production is eastern oysters, bottom culture is the preferred method of farming. Similar to conventional crop farming on land, bottom culture involves selecting areas of the sea floor that provide a natural food supply, necessary currents, minimum exposure to predators, and proper temperature and then "seeding" the bottom with shellfish stock that are left to grow to market size. Then they are harvested with a bottom drag from a boat. Both suspension culture and bottom culture depend on natural food supplies for growing the shellfish being raised.

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Since 1996, the Maine Aquaculture Innovation Center (MAIC) Mussel Suspension Culture Working Group has been meeting to help develop mussel raft technology in Maine. This group consists of about 75 participants who include mussel draggers, lobstermen, clam diggers, urchin divers, and other groups interested in fishing farms in Maine. Due to the pioneering work done by Richard Lutz funded by Maine/New Hampshire Sea Grant in the 1970s there has been renewed interest in mussel suspension culture in the U.S. This is primarily the result of successful culture and sales of mussels in the Canadian Atlantic Provinces where aquaculture development funding has been a priority.

In Maine, early starts at suspension culture were plagued by eider duck predation, poor site selection, lack of culture technology transfer, insufficient capital and lack of an established market in the food service industry for high quality ($0.80/pound wholesale) mussels. Bottom culture of mussels, pioneered by Great Eastern Mussel Farms, Inc., has produced about 4 million pounds annually for the supermarket trade ($0.50/pound wholesale) over the past decade in Maine. Meanwhile, explosive growth of rope-cultured mussels in Prince Edward Island (and presently Newfoundland and Nova Scotia) resulted in over 30 million pounds per year production, the majority of which is exported to the U.S. for the food service market. In fact, the importation into the U.S. of mussels from eastern Canada and New Zealand has been growing each year, contributing to over $20 million in the U.S. trade deficit.

While there has been some growth in mussel raft production in the Pacific Northwest using hatchery-reared Mediterranean mussels (Mytilus galloprovincialis), there was no significant industry in New England with the local mussel Mytilus edulis until recent start-up efforts involving the MAIC mussel working group and Great Eastern Mussel Farms. There were several obstacles to overcome at first, and solutions were tested. In order to increase the acceptability of suspension culture of mussels along the Maine coast; small lease sites were used, and rafts were selected as the structure of choice.

Rafts provided a stable platform for working, they could produce high volumes of mussels in a small area (40 x 40 foot raft yields to 30 tons of mussels per year), and duck predation was averted through the use of a duck predator net. The latter obstacle was especially important to overcome since Maine has one of the largest recovering eider duck populations in the world (over 3,000 rafting ducks inshore from December to April). Lastly, raft culture can take advantage of the vast areas of ice-free deep water along the coast of Maine. The mussels grown on rafts are of superior quality. Wild mussels yield about 10 pounds/meat/bushel versus 24 pounds/meat/bushel of raft-cultivated mussels. Spain, the leader of European mussel production, uses mussel rafts which yield an average of 130 kg live weight of mussels/square meter/year (Hickman, 1992). A variety of float designs are constructed from eucalyptus wood, each averaging about 340 square meters.

MAIC gave a grant of $2,000 to the mussel working group in 1997 to study different types of material for mussel seed collection. In 1998, a private foundation gave the group $10,000 to purchase Spanish graders, socking machines and rope for field trials. This was followed by $100,000 in industry development, including 3 Scottish rafts (kits shipped from Scotland currently at Maine lease sites) 4 wooden rafts, and other smaller rafts along Mainešs coast. To date, harvests have yielded 40 tons of mussels (1998-1999) and projected harvests for next year are 120 tons.

More information on mussel raft culture is provided through "The Maine Guide to Mussel Raft Culture" a 31 page booklet prepared in 1999 by the Island Institute for the Eastern Maine Development Corporation. To obtain a copy of this booklet, contact David Platt at the Island Institute, 410 Main Street, Rockland ME 04841, Telephone 207-594-9209.

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Beals Island Regional Shellfish Hatchery, a nonprofit, government- subsidized educational and research operation, has been instrumental in studying soft-shell clams and educating the public about this resource. The hatchery produces millions of 1/4 to 1/2-inch soft-shell clams each year by spawning broodstock and raising the juvenile clams through to transplant size. To induce spawning, broodstock clams are "shocked" by moving them from 50F seawater to seawater warmed to 70F. The change in temperature causes clams to release eggs and sperm into the water. Fertilized eggs (a two-inch female clam may contain 1 million eggs) are collected and placed in large tanks in the hatchery where they are raised until the clams are 1/15 inch long. They are then placed in floating trays, 15,000 clams per tray, and are transported to the Mud Hole, three miles from the hatchery. The young clams are left in the trays to grow until they reach transplant size. Finally, local clam flats are seeded with the 1/2-inch transplants.

Hatchery personnel teach the general public, town shellfish committees, and clammers about the life cycle of clams and clam flat management. Seeding a depopulated clam flat involves transplanting young clams to traditionally productive areas that now have low clam populations due to overharvesting by humans; natural predation by birds, fish, crabs, moonsnails, sandworms, bloodworms; or poor recruitment The seeded area is covered with nets to keep out predators, and the transplanted clams are left to grow until they reach market size. Clammers benefit from this management strategy.

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The Giant Sea Scallop has long been an important market for Mainešs commercial fishing fleet. In recent years, however, the catch has declined precipitously, and scallop buyers have been forced supplement locally caught scallops with product imported from elsewhere. Maine buyers increasingly are turning to regions in Asia where scallops are cultured.

In 1999, with support from the Federal Government and the Maine Department of Marine Resources, the Maine Aquaculture Innovation Center organized and led a study mission to Mitsu Bay in Aomori Prefecture, Japan, where the Japanese Scallop is intensively grown on longlines. The 35-page report on the trip (cost $10.00) may be ordered from the MAIC office. This report has sparked the interest of commercial fishermen and would-be scallop farmers. By the fall of 1999, several research projects had begun to determine if Japanese scallop spat collection and husbandry methods could increase scallop production in Maine. Collaboration with Japanese scientists is continuing.

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