I should have a few pictures to show tomorrow, but I think my time is coming to an end with this guy. Heavy breathing, white coloration, curled arms all add up to a senescent octo.
The heavy breathing (and usually lethargy) are symptoms of senescence but be sure you check the water. I call the aging color gray because it is different from the vibrant healthy white. You can see the difference in comparative pictures but I notice when only looking at the late in life photos I have taken make the animal look healthier than what I see with my eye.
According to Cephalopods A World Guide, Mark Norman notes body size (assuming this means mantle) of 12cm (about 4.75") and an arm length of at least 60 cm (about 23.5 inches). Unfortunately, it is very hard to establish sizing at their largest if they live out a natural life because they "shrink" visibly during the last couple of weeks after they stop eating. Like all octopus though, the size can vary quite widely. My guess is that 3.5" for the mantle and 15" on the arms has been more typical but all the recorded sizes have been after death.
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