Dr. Roberts recently asked me why I was getting such a low response rate from the treatments. I was seeing between 5 and 50% of the animals become anesthetized. Monitoring the situation I have a few ideas on why. Which I stated in a response to him in a message which is copied below.
I think it was a combination of the warm ambient air temps that caused an increase in treatment temperature which led to animals not opening in the treatment.
I also checked my treatment calculations and the epsom salt concentration was about half. I calculated it fo 5 gallons instead of the full ten. I'll just double the amount of epsom salt to make it the proper concentration. Hopefully it will increase response from the animals.
Brent has also suggested doing sub samples instead of dosing the whole tray to limit exposure by all the animals and reduce the amount of epsom salt we are using. I think its better to dose the whole tray because I can't guarantee that the percentage of animals that open will stay the same. On top of this variable percentage, there will only be 10-20% of the animals brooding at any given time. If we don't treat enough animals we will be more likely to miss spawning effort.
Brent also had some useful suggestions about previous work with the treatments as well as some recalculations of the treatment solution to increase treatment concentration.
Katie consistently saw about 30% response (without dessicating them first. I don't have her data on dessication, but response rate was higher). If we stick with the 5% threshold to see brooders and a 30% response, you'd need to treat 67 oysters to = 1. If the response with dessication is closer to 60%, you can decrease the subsample by half.
It sounds like the oysters may have been too warm to respond--important to bring a thermometer, and probably some ice packs to control treatment temp.
85g/L = ~7 lbs of MgSO4 for 10 gallons.
It can be argued that we only treat half the tray at any given time to limit downstream effects from the treatment which may affect spawning including abortive spawns or gonadal regression. The problem with this is that too see any signs of spawning we would be looking for 1-2 animals in any group to be brooding. I don't think this is a reliable way to determine if the populations are spawning. We would be better served in treating the whole tray to avoid mixups and hopefully have a higher number of brooding animals to strongly suggest that they animals have spawned.