He hasn't eaten in over a week now. A few examples of behavioral changes, he jets around the tank more than I have ever seen him, he used to wander around the glass and rarely jetted anywhere. He seems to have relocated from his cave to sleeping under a rock ledge. At times he will go around like he used to but that is getting rarer and rarer.
Behavior changes, particularly restless/aimless wandering are a sign of senescence. However, the same symptoms occur when the water is uncomfortable. You might try another large water changes since you have removed the pumpkin and double check your salinity and PH.
+1... hope things are improving. @DWhatley - I can't help but wonder - do you still think the pumpkin decoration may be unsafe for an octo tank, despite the LFS selling it and deeming it aquarium safe? I suppose it's hard to tell for sure but wondering if you have experience with "aquarium safe" products being, in fact, unsafe.
We've seen lego toys, and other things used with octos so it's hard to understand the parameters.
I'm sorry to report that Owen passed yesterday. I did another 25% water change early this week and he just never showed any sign of improvement.
What first caught my attention was the bristle worm in the tank seemed to take an interest in him about the same time he stopped eating. Prior to that time, anytime the bristle worm would come around when Owen was eating, he would push him away. The first sign that there was something going on was seeing the bristle worm hanging out by Owen's den. I noticed that about the same time I noticed he wasn't eating. Even the last crab I saw him kill, it wasn't the typical parachute over the crab type of kill. He grabbed it with his arms and kind of held it for 5-10 minutes before killing it. At that time, I didn't think much of it but that was the last time I saw him kill a crab.
I'll post a video of him holding that crab later on.
Your description of Owen's decline are well in line with natural senescence. In cases where we know animals were exposed to poisons, the deaths have been rapid or water changes have shown rapid improvements.
@tonmo I cannot (as I mentioned) recall any poisonings or specific articles about anything other than copper to back up my paranoia about the possibility of painted decorations being toxic to cephs. My fear comes from the fact that we can't/don't test for many water parameters (we have no positive bacteria tests at all) and our aquariums are so small that very small amounts of anything can have a large impact.
Owen was by far the coolest pet I have had. Although it was short it was highly enjoyable having him around. He was very personable and had a way of making you feel bad when you left the tank area. He is actually the second ceph that I have had and way more interactive than the last one. The first octopus I had was a female that laid eggs within 2 weeks of getting her. At least with her it was a definite sign as to what was to come. I guess having had both, I think I would prefer a female given the opportunity to choose.
With that being said, how does one ensure that the octopus they are getting is at the beginning stages of their life? At what age are most wild caught ones typically caught?
I have come to think that it is rare to come find very young octos unless they are by catch from live rock retrieval. Animals that are caught in crab traps or out in the open are typically full grown. Animals easily found while diving are likely females hunting for their last meals before brooding.