FISH FARMING TECHNOLOGY #2
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VIBRATORY SCREENING OF OYSTERS Seed oyster production at The New Jersey Aquaculture Innovation Centre at Rutgers University (AIC) is a large-scale operation by any measure. The 2046 sq m facility next to the Cape May Canal in Cape May, NJ, produces diseaseresistant, fastgrowing seed oysters for commercial grow-out, research, and restoration of native oyster beds. by Kason KekGardner, NJ Aquaculture Innovation Centre, Rutgers University
nnual production is more than 10 million seed oysters to meet customer specifications, in particular those of East Coast commercial oyster producers. Sorting by size for counting and redistribution in the “nursery” is a frequent and essential operation in the seed oyster production cycle. Originally, sorting with a 0.6 X 0.6 m hand-held screener was a daunting task, according to Matt Neuman, lead researcher and technician for hatchery production at the AIC. “It took all day for a three- or four-man crew to complete each round of sorting,” he explains. “And the added weight of seawater mixed with the product took a huge toll on everyone’s shoulders.” The search for a ‘better way’ led to replacing manual screening with a dramatically more productive, mechanical 762 mm diameter Vibroscreen™ circular vibratory screener manufactured by Kason Corporation. With one operator now completing each day’s sorting in less than two hours, the equipment paid for itself in the first season.
Aquaculture innovation at Rutgers
As the leading research and education hub for New Jersey’s aquaculture community, the AIC studies and teaches methods of commercially raising seafood, benefiting a wide range of stakeholders – from aquaculture entrepreneurs and restoration specialists, to governmental resource managers and nongovernmental organisations, to the fishing industry. Among AIC’s projects is mass culturing of micro-algae using algal photo-bioreactors to increase yields of biochemical compounds with high potential value for food and pharmaceutical applications, as well as for shellfish (i.e., oysters) cultured for human consumption.
Seed oyster production: mimicking and accelerating nature
The Eastern Oyster (Crassostrea virginica) is among the shellfish species successfully cultured at the AIC using a micro-algae diet. The facility has been producing seed oysters from this strain since 2008. Seed oysters are small oysters, about 2–25 mm long, provided primarily to oyster growers for the half-shell market. They are also used to restore natural oyster populations or natural ecosystems, and for research. While natural oyster populations in the Delaware Bay spawn in late June or early July, at the AIC broodstock (adult oysters which produce baby oysters) are moved into temperature-controlled tanks in January, given plenty of microalgae food, and are ready to reproduce by late February. Fertilised eggs become microscopic oyster larvae, which are raised in filtered, sterilised seawater in 5 678 litre culture tanks. After two to three weeks, the larvae metamorphose into juvenile oysters called “spat.” The growth cycle from spat to seed oysters takes several weeks to several months, depending on their intended size. Where oysters naturally clump together, AIC’s methodology yields individual oyster “singles” suitable for the half-shell market. The first sorting operation in this growth cycle occurs when juvenile oysters are still under one millimetre in size, after spending about two weeks in filtered seawater in large “downweller” tanks, with regular feedings of cultured algae. Manual sorting in the downweller tank with a 0.3 X 0.6 m hand-held screen works efficiently for distributing the oysters at this tiny size to a series of 457 mm diameter “upweller” silos fed by raw seawater and whatever food it naturally contains. As they grow, juvenile oysters are regularly sorted by size, counted, and redistributed in the upwellers to optimise growth and survival. The number of seed oysters placed in individual silos is based on volume determined by sub-samples. At full production late in the growth cycle, the AIC has 130 upwellers in use. The AIC supplies some growers with seed oysters as small as two millimetres for cultivation in their
10: 2 cm size oysters are ready for commercial farmers to place in the Delaware Bay to finish growing out
46 | July | August 2016 - International Aquafeed