As you open the package, note the temperature of the seed. It certainly wouldn’t hurt to use a thermometer, but if you don’t have one just make sure the seed is not touching the gel packs. The goal in shipping is not to cool the seed way down, but rather prevent it from heating up in transit. If, depending on the time of year, the oysters are in the 50’s to high 60’s F, they should be fine. It is important make sure the oysters warm up to the ambient water temperature before immersing them. Keep them out of direct sunlight, but let them slowly warm up in the shade before dividing them up and putting them in the water.
How do I check the counts and assess viability and growth of the seed?
Assessing Viability, Counts, and Growth
We work very hard to insure that all of the seed we ship arrives healthy and grows well for all of our customers. If there are questions about viability, performance, or counts, we will make every effort to correct errors or problems, provided we are informed of the issue in a timely manner after receipt of the seed. This means that counts should be verified before transfer to the nursery system, viability assessed within 2 weeks, and growth determined within 4 weeks of receipt.
We are very happy to provide guidance and answer questions to help you make these assessments. Feel free to call us at 855-563-1456 or email us at firstname.lastname@example.org.
Counting seed when it arrives
Your seed will arrive, depending on size, either wrapped in a damp handiwipes inside a Ziploc bag, or in a Ziploc, which has handiwipes in the bottom of the bag to soak up excess moisture. It is important to note the condition of the packaging when you open the box(es). We go to great lengths to ensure that the seed is kept up above and not in direct contact with the gel packs. The seed packs should be cool, but not cold—it is a good idea to check the temperature. It should be between 50 and 65 degrees. If the seed is colder than the water at your nursery, make sure you let it warm up in the shade until is within a degree or so of your ambient water temperature before immersion.
Materials and equipment:
- Two scales. One accurate to 0.01 grams (these usually go up to 200 grams or so) and one that goes up to 2 to 4 or 5 kg, depending on how much seed you receive. This one should be accurate to 0.1 or so grams.1
- Several petri dishes or small flat plates which will hold a small amount of water.
- Some kind of probe to disperse and move oysters around.
- A dissecting microscope is great but not necessary. Even for small seed a magnifying glass (preferably one on a stand or holder) works fine.
- A mesh bottom sieve or sieves depending on the quantity of seed.
If you are purchasing significant quantities of seed, we highly recommend investing in the appropriate scales, not just for checking seed shipment counts, but also to use when grading or thinning as they grow. It also will allow you to more accurately distribute your seed initially.
- If you receive multiple groups of seed with different counts (oysters per gram), it is important to count each group separately.
- Start by recording the weight of each sieve to be used or use the scale (if equipped) to determine the tared weight of the seed.
- Unpack the seed and transfer it to tared sieves, gently brushing off the handiwipes and removing seed from the sides of the Ziplocs.
- Weigh the sieve and seed and subtract the sieve weight if not already subtracted automatically (tared) by the scale.
- Using a small spoon or spatula take 3 to 4 small samples2 from different parts of the sieve containing the seed, place these on your sampling dishes to determine the weight of each seed sample without its dish. These seed samples should be large enough so that you are counting 150 to 200 oysters in each sample. This can be estimated from the weights and counts accompanying the shipment.
- Add a small amount of water to each sample so the seed can be easily moved around and counted using a probe. One handy method for counting is to put a line on the dish bottom at the outer edge of the dish, perpendicular to the circumference. Spread the oysters around the outer edge of the dish and starting at the line count around the dish back to the line.
- Calculate the average number of oysters per gram from the 3 to 4 replicate samples, and multiply the average by the total seed weight for each sieve. Total the seed weights for the sieves for each group of seed received and compare the totals to the numbers given on the packing slip.
If there are multiple bags of oysters for each group, it may not be necessary to count 3 replicates per sieve, but there should be 1-2 samples taken from each packet of seed. Variation in replicate counts is most likely due to the moisture level of the seed taken from different places on the sieve.
Depending on the receiving conditions, it can take several days for oyster seed to acclimate, but you should certainly know if the seed is viable within a week or so. Production of feces is always a good indication that the oysters are alive and feeding, but may not be evident early in the season when water temperatures are cold, and/or the seed is deployed in gear where wave action is a factor. Direct observation is always best. Place a sample of seed in a small dish and, if the water is cold, let it slowly warm up. Observe the oysters with a good magnifying glass, or preferably, a dissecting scope. You should see the oysters open up and start pumping. When you poke them with a probe, they should close up. You don’t want to see unresponsive “gapers.”
There are many factors that influence the growth of seed oysters, including temperature, salinity, food availability, stocking density, and flow rate of seawater through the oysters, as well as genetics and whether or not the oysters have been stressed. Oysters that are stressed by low oxygen, low or high temperature, or other factors can sometimes subsequently exhibit poor growth if they are not killed outright. If too much time passes between receipt of the shipment and assessment of growth, it is difficult or impossible for us to know if there was a problem with the seed shipment or the oysters were stressed after their arrival.
At least every other day after stocking the seed, they should be sampled and looked at under magnification to see if they are putting on new shell edge. New growth is clear and fragile and it is sometimes best seen by illuminating the oysters from below or behind. The vast majority of the oysters should be showing new edge if they are healthy and the growing conditions are good. To get a more quantitative assessment, once per week you should sample the seed and determine the average count per gram. Depending on the time of year and conditions, you should see a declining number of oysters per gram. If your site is good and the oysters are properly stocked, at the height of the growing season you should see the count per gram halved multiple times per week.
We want to reiterate the importance of contacting us if you have any questions or concerns about your seed or the information provided here. Again, we are very happy to provide guidance and answer questions to help you make these assessments so don’t hesitate to call us at 855-563-1456 or email us at email@example.com.