Time to fatten the oysters up!
Now that I’m done with my heat shock, my next step is to condition the broodstock. Conditioning involves gradually raising water temperature and increasing feeding so the oysters develop lots of high-quality gametes. Laura agreed to condition for me while I’m gone, so today I wanted to set everything up for her.
Here’s what I did:
Turned water flow back on
When I came in, I noticed the water in Tanks A and B were unusually warm. I checked and they were getting no water flow. I turned the water back on. Because of this unintended shock, I want all oysters to remain in normal conditions a few days longer before conditioning.
I checked oyster mortality (none dead from both pH treatments or heat shock!), vacuumed fecal matter and placed all remaining oysters from the ambient holding tank into bags. Here are the final oyster counts:
Table 1. Number of oysters in each bag per tank. Numbers 1-6 refer to the tank used for pH exposure, “Heat Shock” refers to oysters exposed to 40ºC for one hour, “Full Amb” are oysters kept at ambient temperature and pH conditions and were not used in any experimental set up, and “Spare” refers to oysters that are not in bags but in tanks.
Drained experimental heating tank
Checking the AVTECH, I learned that the flow could not be full blast if I wanted the heater to warm it up fast enough. Even when flow wasn’t full blast, the setting on the heater was at least 1-2 ºC warmer than the measured water temperature. This is important to keep in mind when conditioning.
I drained and cleaned the tank used to test the heater’s efficacy to use as the heated water tank in my set-up. This is because the tank had insulation around it, and I didn’t want to go through the extra effort of adding insulation to the tank that’s already there.
Calculated new feeding rate
The handbook suggests that the ration of algae (g/day/adult oyster) is equal to 4*(mean dry weight)/100. I didn’t have any dry weights, but I made the assumption that my dry weight was one-tenth my live weight, which is an assumption Reed’s makes as well. Based on this calcuation, I got that I need 0.3 g/day/adult of dry weight algae. With about 65 indivduals per tank, I need 19.5 g/algae/tank, so 39 g/algae for all of my oysters everyday.
On the Shellfish Diet website, it says that the dry weight is 8%. This means that there are 8 g dry weight algae for every 100 mL Reed’s paste. For 39 g/day of algae, I need 487.5 mL Reed’s paste daily in a 200-L culture tank.
Calculated dosing rate
Figure 1. Dosing pump used to feed oysters.
I’m using a HANNA BL15 dosing pump that has an output of 15.2 L/hour. I want to get through 200 L in a 24 period. I calculated that I need to set the pump’s flow rate between 55% and 60% to accomplish this.
Calculated flow rate
The FAO handbook recommends a flow rate of 1.25 L/min for a 150-L tank with 50 oysters. That equates to 25 mL/min/oyster. I have 65 oysters in 100-L tanks. Having too high a flow rate may flush out the food necessary to condition, while having too low a flow rate would keep waste in the tanks too long. To balance feeding with flushing, I settled on a flow rate of 1.2 L/min for my tanks when conditioning. This mean each adult has a flow rate of 18.45 mL/min, and there is a 83.3 minute full-tank water turnover.
Prepared separate algae header tank
Because my oysters need to eat so much, there’s no point sharing an algae header tank with Laura’s oysters. I got permission from Ryan to use a spare 200-L tank. I placed it next to another outlet since I’ll need the outlets for an aquarium pump to properly mix and aerate the algae.
Figure 2. 200-L tank for algae.
Because the dosing pump was farther away from the header, I needed to reattach a longer tube. I found a long piece of tubing and attached it to the bottom of the dosing pump. This tube will reach to the new header tank. Since I won’t need to use that header tank for a few days, I placed the tube back in the algae header tank I’m currently using.
Figure 3. Longer tubing outfitted for new header tank.
Set up heater header tank system
Laura helped me by plugging the heater into an outlet and placing it in the insulated header tank. We outfitted PVC onto the header tank’s outflow that directed water into Tanks A and B below.
Figure 4. Heated header tank system. Water heated in the header leaves through the tank’s outflow and is fed into Tanks A and B below through PVC tubing.
Because I didn’t need to use the calculated 1.2 L/min flow rate just yet, I set flow in both tanks to 0.8 L/min. To do this, I adjusted the outflow of the header to 1.6 L/min, and checked that the inflow to the two tanks was at 0.8 L/min.
Ordered extra equipment
A full and productive day! I just need to spell out my conditioning plan more clearly so Laura and Ryan can proceed.