How to Grow 2mm Oyster Seed

Grow 2mm Oyster Seed

This article describes a method of raising 2mm oyster seed obtained from the hatchery without utilizing power or pumps. This method is suitable for use by the serious hobbyist or professional oyster grower.
It utilizes a special nursery cage within a protective standard HDPE mesh oyster bag. The nursery cage made of off the shelf materials, obtainable from any hardware or lumber store.

Like most oyster gardeners (and I prefer the title oyster rancher), I have always started with ¼”(6.35mm) oyster seed grown in HDPE 4mm mesh bags. 1000 ¼” seed typically costs about $35. As I started to go semi pro and growing thousands at a time, this started to be a not insignificant expense. So when Oyster Seed Holdings (http://www.oysterseedholdings.com) on Gwynn’s Island in Mathews County started offering 2mm seed for $6.50 a thousand, I decided to try my hand at growing these very small seed. Why do it?
Pros: Cheaper, lots more oysters.
Cons: More labor, more material, 20000 minimum order, lots more oysters.
One practical way for the not so obsessed gardener to get around the too many oyster seed problem would be for several people to get together and split the seed and save money.

My first attempt was late fall. I purchased polyethylene mesh oyster nursery bags from Aquatic Eco-Systems wonderful aquaculture supply website (http://www.aquaticeco.com/). I placed 25000 seed in five of these fine mesh bags, then placed those inside five 9mm mesh HDPE bags. These I suspended off my dock. The first thing I noticed was it was hard to keep the inner bags spread out, and that the oysters would bunch up and get fouled fairly quickly. However within a month I had gone from about a pound of oyster seed to 23 lbs. By spring they were transferred out of the fine nursery bags to 4mm HDPE mesh bags. However I estimate that I only had 20% survival from fall to spring. Still, wrangling 5000 oysters that summer was a challenge.

Undeterred, I purchased 30000 that spring, bought a coarser mesh nursery bag which I hoped would help with the fouling. This time I secured the bags by their corners inside a 9mm HDPE bag. I came back a week later, and found no oysters. Something had made holes in the polyethelene nursery bag , apparently by spreading the fibers of the bag apart. I suspected that blue crabs had been able to just reach through the HDPE mesh and had a crunchy snack of popcorn oyster seed. I decided I needed a new approach.

The successful method involves a western cedar box covered with standard fiberglass window screen, which is fastened with monel staples. The rectangular box is constructed so that it will fit inside a standard oyster HDPE mesh bag. The screen is separated from the mesh of the HDPE bag by the thickness of the cedar boards, preventing predators from reaching through the mesh and contacting the screen. The box bottom and top are made from 1”x 2” picture frame like rectangles fastened in their corners with stainless steel screws. The top and bottoms are covered with the screen, which is fastened so the screen material forms the hinge of the box. The box is then fastened shut with a stainless steel ¼” carriage bolt and wing nut.

5000 2mm oyster seed were placed in each of these nursery trays. The wood provides enough buoyancy that the bags float on their own. I decided to add two .75lb weights to fasten to the outside of each HDPE bag to get them to float a bit deeper. These were made by pouring concrete ready mix into 12 “ sections of ¾” pvc pipe.

The weather was very hot, and once in the water the screen fouled quickly. I had to briefly pressure wash them once a week, and they probably could have benefited from more. But by the third week they were ready to transfer to 4mm HDPE mesh bags. There was no discernable mortality. The nursery trays screening appeared to be able to raise many more 2mm oyster seed. I plan to try more this fall.

This method seems to be a quick, easy, inexpensive, green method for raising 2mm oyster seed to a size that can be raised in standard oyster grow out bags.

2mm seed can be contained in commercial small mesh HDPE bags. But the 1.5mm bags have an actual open area between the mesh of only approximately 25%, severely limiting water flow and hastening fouling. The nursery bags fiberglass screen has over 70% open area between the mesh, allowing for better flow.

Week One:

Week two

Week Three, ready for transfer to 4mm bags:

Materials:
Each nursery tray will require two 8’ sections of 1”x 2” western cedar (actual measurements about 1 ½” x ¾”), four 1 5/8” stainless steel screws, four 2 ½” stainless steel screws, fiberglass window screen, one 2 ½” stainless steel ¼” carriage bolt and one stainless steel or nylon wing nut, 5/16” Monel staples (Lowes). You will also need to use the scrap cedar and enough 1 5/8” screws to fasten the scrap to the side of the tray where the screen is on the outside of the tray to keep it away from the mesh of the protective oyster HDPE bag. An approximate price list follows:

Materials Number Price Each Subtotal
1"x2"x8' Western Cedar Board 2 $3.25 $6.50
Fiberglass Screen, 2 trays per pack 0.5 $6.00 $3.00
Stainless steel 2 1/2" screws 4 $0.10 $0.40
Stainless Steel 1 5/8" srews 20 $0.10 $2.00
Stainless Steel 1/4" Carriage Bolt 2 1/2" 1 $5.00 $5.00
Nylon or Stainless wingnut 1 $1.00 $1.00
5/16" Monel Staples 100 $0.02 $1.50
Tray Grand Total $19.40

In addition you will need one HDPE 3/8' or 1/2" mesh bag $7.00
Optional PVC pipe and concrete mix for the weights $4.00

Method:

1: Measure and cut cedar boards.
2: Fasten each rectangle tray halve together with one screw in each corner through predrilled holes. Note that one half of the tray is fastened through the ¾” width of the boards, the other through the 1 ½” height.

3: Place the two halves of the tray together to make sure you have a tight fit. 2mm oysters are small. You can twist the pieces a bit, and you can try different sides against each other to achieve the best fit.
4: Lay rectangles on a firm surface. First staple the screen to the bottom of the bottom half of the tray. Keep the screen tight. Next staple the screen to the edge of the long axis of the bottom tray, especially near the top of the edge. This forms one half of the hinge. Turn the bottom half over so the stapled screen is down. Next lay the tray halves next to each other with the screen hinge between the two trays. Using scrap pieces temporarily shim up the top half tray until it is about 1/16” lower than the top of the bottom tray half. When the top tray half is folded over, this will help make the hinge tight. Staple the screen generously, especially on the inside edge of the top half tray where the oysters have a tendency to get trapped under the screen. Also staple the screen on the top half tray near the edge next to top of the bottom half tray to form the other side of the hinge. Be careful about wrapping the screen, it is easy to get it backwards and not form the hinge or the box. Believe me. Look at the illustrations carefully, and do a temporary layout before you staple.

5: Drill a 5/16 hole through the tray on the long side opposite the hinge for the ¼” bolt to hold the tray halves shut.

4: Using scrap pieces (where possible) of 1” x 2” cedar and 1 5/8” screws, buildup the bottom of the bottom half of the tray where the screen is on the outside of the tray to keep the screen away from the HDPE mesh. This will also help better seal the screen where the oysters spend most of their time. Leave a gap for the wing nut.

5: If you have a router or plane, I recommend rounding or easing the outer rim of the edges of the top and bottom. This makes sliding it in and out of the HDPE mesh bags much easier, as the square edges tend to get hung up in the mesh.
6: Make sure that the carriage bolt is loose enough to allow you to open the trays. The wood will swell when it gets wet. If it is too loose however, the hinge will be loose.

7: In warm weather you will need to pressure wash the fouling off the screen at least once a week. I tried using a hose with very limited success, but my water pressure is low, and I have a 150 foot hose run. My relatively low power pressure washer did not seem to bother the oysters. I was able to clean the trays adequately without taking them out of the HDPE bags. The 9mm and 13mm HDPE bags worked equally well. Neither demonstrated predation.

I welcome your comments.