a few updates--
I have been very concerned about octopus prime this week. he seems to be out of his den for more of the day than usual, yet spends most of that time in one or two favorite spots on the glass, with his arms curled up looking a little pale. He still does flash and change colors regularly in response to activity occuring near him, but he just doesn seem like his normal "constantly exploring self," and i realize that these are early signs of the end of his life.
I put a fiddler crab in a few days ago (he usually eats 1, sometimes 2 a day) and another one in yesterday, seeing no trace of the first. But now i see that neither have been eaten. Octopus prime is currently curled up very small on a rock on side of the tank opposite his den, sleeping. very disconcerting.
On an unrelated note, i put in 25 mysid shrimp i had ordered from aquaculturestore as a treat a couple weeks ago. He vorciously ate 6-10 of them right away and gradually seemed to lose interest. in the subsequent days he would take occasional swats at them but not try too hard to catch any. Now there are still a few swimming around, occasionally bumping right into him! For a while he was clearly only interested in the fiddler crabs, but as i said, now he seems to have very low appetite all together
I know OP's gender has been up in the air, but this kind of non-nesting behavior would rule out a senescing female, correct?
I do realize that water quality may also be an issue, especially if a few shrimp have died and decayed. Also, lending to the water quality theory, last week I awoke and saw that he had inked (probably in response to me violently swatting the alarm clock!).
i had never seen him ink before, but i netted it right away and changed 20% of the water volume later that day.
any speculations are more than welcome
here is a picture of him, relatively normal last week:
and one of him today, hiding in a rock, looking pale and asleep, yet far from his own den...