It’s the engine that drives our business. For nearly 30 years we have doggedly pursued our goals of understanding the American oyster’s life cycle, and using the best available technology to reliably provide disease free, disease resistant, and naturally grown juvenile oyster seed. In 2013 all of our seed orders were filled and shipped on time.
Oysters eat microalgae (single celled plants) by filtering the cells from the water.If the hatchery is the engine that drives the business, microalgae fuel the engine. We have two culture systems, one for growing small cells that are the primary food for the young larvae, and a second, proprietary system for growing the bigger cells we feed to our broodstock, older larvae, and the young juveniles before they leave the hatchery.
We use a variety of broodstock lines including our own oysters grown in the Damariscotta River that we selectively breed for shape, cup depth, and rapid growth. We also maintain a state approved broodstock quarantine facility which allows us to safely hold oysters from other parts of the East Coast where oyster diseases are endemic. These stocks include the HASKIN NEH® line from Rutgers University and disease resistant tetraploid oysters from the Virginia Institute for Marine Science Aquaculture Genetics and Breeding Technology Center. The oysters are ripened by holding them at elevated temperatures with an ample supply of food for several weeks. Broodstock conditioning typically begins late in the fall and as the hatchery season progresses we rotate different groups of oysters through the system to ripen and spawn.
Ripe oysters are placed in their own basins and stimulated to spawn by rapidly cycling the water temperature. We typically sacrifice some males from the desired genetic line and add stripped sperm to the water in the basins to help initiate spawning. The oysters spew their gametes into the water turning it milky. The females are easy to identify because the eggs have a distinctly granular appearance, and the egg basins are pooled into larger buckets where, if necessary, more sperm is added to insure good fertilization. The fertilized eggs are then washed on a 20 micron screen and placed in calibrated buckets where they are counted and placed into the larval culture tanks. Our first spawn of the season is usually late in December or the very beginning of January, and our last is generally late May or early June.
Within 48 hours after fertilization the oyster embryos grow clear shells around themselves and a ciliated appendage which they extend from between the two shell margins for swimming and feeding. The larvae are fed daily and the tanks are drained on special sieves every 48 hours to change the water and grade the larvae on sizing screens. At each “drain-down” the larvae are restocked at the appropriate density to maintain rapid growth. At 48 hours the larvae are retained on a 50 to 60 micron screen (.0024” to .0029”). By about 14 days the larvae are held on a 200 micron (.0083”) screen and they develop two “eyespots” that guide them away from the light towards the bottom, and a “foot” that they use for crawling. They are now ready to undergo a metamorphosis and become a bottom dwelling, non-motile oyster. This process is called “setting.”
The ready-to-set larvae are placed into shallow, fine-mesh floating screens. A layer of finely sieved oyster shell spread on the screens provides the substrate for attachment and metamorphosis. Once set, they quickly begin to feed and grow as “post-set” juveniles and after about a week on the setting screens the baby oysters are screened to separate them from the shell chip and returned to the floating screens for another week or so.
With floating screens the water with fresh food and oxygen enters from the top and circulates before passing down through the screening. When the young oysters are big enough they are moved to an “upflow” system. First they are put in “passive” upwellers where the water is drawn up through a layer of seed using air lifts. The biggest seed is grown in “forced” upwellers where the culture water is actually pumped up through a more concentrated mass of animals. Upwellers are extremely space efficient and can provide very uniform growing conditions.
The way to produce disease resistant seed is to use disease resistant broodstock. We only spawn oysters that are believed to be disease resistant. If not intensively selected for resistance at Rutgers University or the Virginia Institute of Marine Science (VIMS), they are survivors from areas where oyster diseases are endemic. We produce both diploid (2N) oyster seed which have the normal two sets of chromosomes, as well as triploid (3N) oyster seed with three sets of chromosomes. Triploids have been shown in some cases to grow faster than diploids and because they are sterile, their meat yield and quality tends to be better during the summer months when the diploids are spawning. Our triploid seed is produced “naturally” from tetraploid (4N) oysters with four sets of chromosomes that are crossed with diploid (4N) broodstock. Our tetraploid broodstock is obtained from the Virginia Institute for Marine Science Aquaculture Genetics and Breeding Technology Center. Triploid seed is sold under license from them as well as 4C’s Breeding Technologies, Inc. License fees apply to any seed generated from the disease resistant broodstock obtained from either Rutgers University or VIMS.
All of the seed we sell comes directly from the hatchery. The hatchery seawater is highly filtered and irradiated with ultraviolet light. This high level of water treatment, strict protocols for handling broodstock and fertilized eggs, and regular pathology tests allows us to guarantee that the seed we ship is disease free. We sell seed retained on sieve sizes ranging from 1.0 mm to just under 3.0 mm priced per thousand oysters, and shipped FedEx next day.
Oyster Farming Sustainability
Maine Oyster Farm – Mook Sea Farm prides itself on delivering a sustainable product. Our oysters are grown in the clean, fertile waters of the Damariscotta River, which for thousands of years has been renowned for some of the world’s best oysters. Our oysters feed on naturally available phytoplankton. We use no artificial feeds or chemical additives. In fact, oysters have an amazing capacity to filter the water and actually improve water quality by removing excess nitrogen and carbon from the water. We take our role as environmental stewards very seriously and in 2010 we switched from bottom culture to raising all of our oysters in OysterGro™ cages. This eliminated the potential for ecological damage to the river bottom from repeated dragging as well as to the water column from the effects of increased turbidity caused by constantly re-suspending bottom sediments.