monicaswizzle
Premium Member
Since my black caps haven't spawned yet (I actually hope they hold off until after a 4 day weekend away in early April), I am getting to practice my rotifer culture technique while I wait. (I am feeding the harvested rotifers to some unexpected rosy barb fry that showed up in one of my FW tanks. Despite using salt water rotifers the barb fry clearly are feeding on them, so they must survive in the FW long enough to act like prey.)
Anyway, the main trouble I seem to be having is getting any kind of accurate estimate of rotifer density in my culture bottles. I am using two one-liter glass bottles that are nice since the heavy glass allows me to sink them into a heated tank of FW. Since I don't actually need rotifers at the moment, 2 liters of culture space is plenty.
When held up to the light the glass jars are clearly "teaming" with rotifers, but I get pretty low counts per ml when I try to quantify. I have been trying to quantify the density by: 1) briskly stirring the liter jar of rotifer culture water, 2) inserting a plastic pipette with a bulb reservoir and "sucking up" about 2 ml of culture water, 3) as rapidly as possible (so as not to alter the density) returning water from the pipette to the culture jar until exactly one ml is in the pipette, 4) dropping 2 or 3 drops from the pipette into the wells on my 10 well depression counting slide and 5) counting the rotifers on the slide under my dissecting scope.
Most of the time I get counts between 10 and 20, which by my calculations means 10-20,000 rotifers per jar, which may be true, I don't have the experience to know what 10-20k per liter would look like. However, it isn't uncommon for me to get counts of 5 or 6 and earlier today I only had 2 rotifers in the ml sampled. That clearly is wrong--I can easily tell that there are well over 2,000 rotifers in the liter jar.
I suspect that something in my technique is causing the ml on the slide to be at a lower density than the average ml in the jar. I am not sure how adept rotifers are at evasion, but I have wondered if they either: 1) swim away from the pipette faster than I can suck them up, 2) drop rapidly in the water column within the pipette and return to the culture vessel when I eject 8 or 9 drops back out of the pipette to have exactly 1 ml in the sample or 3) do both of the above.
Assuming my "top end" counts are accurate and there are really 10-20,000 rotifers in each liter jar, it shouldn't be common to get samples with only 5 or 6 in a ml, should it? I am not sure how much "randomness" I should expect in any one sample, but since I mix the jar immediately before taking the sample, I would expect extra low (or high) readings to be very rare events.
Anyone with experience with this problem? Any suggestions as to how I can make the samples more uniform (and accurate), or do I simply need to take four or five samples and average them to get a better reading? (I can do that, but since I count the rotifers before I head out to work in the morning, I would rather only take one or two samples per jar.)
Thanks!
Anyway, the main trouble I seem to be having is getting any kind of accurate estimate of rotifer density in my culture bottles. I am using two one-liter glass bottles that are nice since the heavy glass allows me to sink them into a heated tank of FW. Since I don't actually need rotifers at the moment, 2 liters of culture space is plenty.
When held up to the light the glass jars are clearly "teaming" with rotifers, but I get pretty low counts per ml when I try to quantify. I have been trying to quantify the density by: 1) briskly stirring the liter jar of rotifer culture water, 2) inserting a plastic pipette with a bulb reservoir and "sucking up" about 2 ml of culture water, 3) as rapidly as possible (so as not to alter the density) returning water from the pipette to the culture jar until exactly one ml is in the pipette, 4) dropping 2 or 3 drops from the pipette into the wells on my 10 well depression counting slide and 5) counting the rotifers on the slide under my dissecting scope.
Most of the time I get counts between 10 and 20, which by my calculations means 10-20,000 rotifers per jar, which may be true, I don't have the experience to know what 10-20k per liter would look like. However, it isn't uncommon for me to get counts of 5 or 6 and earlier today I only had 2 rotifers in the ml sampled. That clearly is wrong--I can easily tell that there are well over 2,000 rotifers in the liter jar.
I suspect that something in my technique is causing the ml on the slide to be at a lower density than the average ml in the jar. I am not sure how adept rotifers are at evasion, but I have wondered if they either: 1) swim away from the pipette faster than I can suck them up, 2) drop rapidly in the water column within the pipette and return to the culture vessel when I eject 8 or 9 drops back out of the pipette to have exactly 1 ml in the sample or 3) do both of the above.
Assuming my "top end" counts are accurate and there are really 10-20,000 rotifers in each liter jar, it shouldn't be common to get samples with only 5 or 6 in a ml, should it? I am not sure how much "randomness" I should expect in any one sample, but since I mix the jar immediately before taking the sample, I would expect extra low (or high) readings to be very rare events.
Anyone with experience with this problem? Any suggestions as to how I can make the samples more uniform (and accurate), or do I simply need to take four or five samples and average them to get a better reading? (I can do that, but since I count the rotifers before I head out to work in the morning, I would rather only take one or two samples per jar.)
Thanks!
