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Octopus Tank Dimensions Discussion

DWhatley

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#1
I would like to start a discussion on tank size for octopuses. The intent is to come up with a forumula for minimum length, height and possibly width without discussing volume. Volume is essential to water quality, of course, but the intent is to try to define a shape based upon something like arm and mantle size and possibly species (active vs inactive?).

I would prefer that suggestions come from members who have kept and observed at least two species in the home aquarium environment (no GPO thoughts for this topic - good topic but outside my intent) but solicit questions and ideas from everyone.
 

neurobadger

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#2
I think it would be a good idea to provide a list of armspans and our current standards for octopus species. People can plot them and figure out a formula.
 

Thales

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#3
Not to take away from the effort, but formulas like this never seem to hold up over time because there are too many variables. Watts per gallon, pounds of rock per gallon, inches of fish per gallon, etc all gone the way of the dodo because though they seem informative, they are missing something. For cuttles people are always looking for the minimum size tank they can be kept in, but the answer is more complex given their different needs at different sizes. For both octos and cuttles, I usually keep them in a smaller tank when smaller and move them to a larger tank when bigger because I think doing so provides for them better than keeping them in a big tank all the time.

The word 'standards' also makes me nervous, and would feel much more comfortable with 'recommendations'.
 

neurobadger

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#4
Thales, what I was thinking about was their needs as adults. I don't know what a smaller tank provides that can't be provided in a big tank.
 

Thales

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#5
In a smaller tank you can know where the animal is so you can be sure it is healthy, and to make sure it is feeding. A small animal that is fantastic at hiding can vanish in a larger aquarium and may not be seen for months or ever again.
 

neurobadger

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#7
Well, to start, here's some data for average armspans of some commonly kept octopuses:

Octopus bimaculoides: 23in
Octopus joubini:9in (18in armspan?)
Octopus briareus: 50 cm (about 21in)
Octopus vulgaris: 1 m (39in)

Whether we should include a subsection for stuff such as mimics, wunderpus, and blue rings, I have no clue.

DWhatley also posted a blog post sometime back with the recommended tank sizes for some animals:

Octopus vulgaris - Crepuscalar - Caribbean - 130+ gallons
Octopus briareus - Crepuscalar - Caribbean - 65+ gallons
Octopus bimaculoides - Diurnal - West Coast Pacific - 50+ gallons
Octopus hummelincki - Diurnal - Caribbean - 50+ gallons*
Abdopus aculeatus - Diurnal - Indonesia - 45+ gallons
Macropus sp - Indonesia - Nocturnal - Indonesia - 45+ gallons
Octopus mercatoris - Nocturnal - Caribbean - 20+ gallons
Plugging in a few points on a graph (paper, sorry), I see that there may be an additional factor that may not be considered: the circadian cycle of the octopus. Crepuscular octopuses seem to require bigger tanks than diurnal octopuses, which require bigger tanks than nocturnal octopuses.

Correct me if I'm wrong; I'm just graphing data here.
 

neurobadger

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#8
As a function of armspan, I get these equations:

Crepuscular: y=(18/5)x - 80, where y is the gallons and x is the armspan (factoring in GPO, 3m and 1000 gallons!)
Diurnal: y=(1/5)x + 39
Nocturnal: y=(1/2)x - 5
 

CaptFish

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#9
Crepuscular: y=(18/5)x - 80, where y is the gallons and x is the armspan (factoring in GPO, 3m and 1000 gallons!)
Diurnal: y=(1/5)x + 39
Nocturnal: y=(1/2)x - 5
That doesn't work.

I had a 36" diurnal Caribbean octopus so his y=46.2 soooo are you saying i needed an aquarium that is a 46.2" cube, 326 gallons?
46.2" by ?" by ?" a 55 gallon is 48 x 12½ x 21 which would have been way to small.

I like the idea but it needs to be more complex.
 

neurobadger

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#10
The y is gallons, actually, and that works out to about 60 gallons, which is still pretty horrifically small I think.

It's pretty imperfect calculation, I admit.
 

DWhatley

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#11
I am hoping for discussion on observation more than calculations with what we have as animal size data. As Rich points out, standards have too many ifs (I currently have a joubini that is no longer dwarf size and have had O. hummelincki that were). However, a guide is needed to be able to evaluate housing. I find the water volume (which works acceptably for water control) does not take into consideration freedom of movement (and I don't know that this is important as an animal ages, hence the request for keeper comments). Tanks come in a wide variety of shapes (and if you have seen some of mine you will agree many are commonly available :grin:) so a 60 gallon cube provides a different housing than a 60 breeder. I don't expect the tank police (:grin:) to use any outcome of the discussions but I would like to summarize what we find and point requests to the thread and summary.

Thaleeees (:wink:) brings up a point that I have not put into specifc thought but has been tickling my brain as I have been thinking on this (Little Bit's excessive size has had me monitoring her tank needs and rehashing the need for recommendations). It may be that providing the same proprotional space as an animal grows is the ideal set up. Tangentially, this is what happens when a small animal is kept in a "critter keeper" initially and then freed to a larger tank but perhaps progression is desired beyond that. I don't have the answer but am hoping for discussion based on anticdotal summary of observation.
 

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