To determine the flask's carrying capacity for rotifers in the absence of water fleas, you would typically need specific data from an experiment or study that outlines the dynamics of rotifer populations under such conditions. Without that detailed context or data, accurately pinpointing a specific number is not possible.
If this question comes from a specific study or lab exercise, please refer back to that source to find the relevant information regarding the carrying capacity for rotifers. If you're looking for a guess based on general knowledge, I would recommend checking the parameters of the given experiment to see which number is most closely aligned with the findings or discussions.
If you can provide more context or clarify the source, I'd be happy to help further!