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Tank size and overfeeding


Haliphron Atlanticus
Staff member
Moderator (Staff)
Mar 17, 2003
On this and other lists I have frequently argued the need not to over feed and octopus and the need for stable large tanks. I just want to reenforce that message with a description of what happened to me over the weekend.

I have a large O. rubescens that we reared from a field captured juvenile. It is housed now in a 50 gal tank with canister filtration and the entire system is kept in a 15 C walk-in coldroom. The system has been running 9 months and is rock stable with respect to water parameters.

Last week couldn't find any live grass shrimp, the animals usual food, so I gave it a piece of frozen tiger prawn about the size of a golf ball. The food was quickly devoured and I thought all was fine. The next morning the animal looked distressed with rapid, heavy pumping of the mantle. It was barely hanging onto the side of the aquarium with just a few suckers. There were lots of feces in the tank and ammonia had spiked.

I used a fine net to remove all the organic material I could and did a 20% water change immediately with what cold water I had. By evening I had cooled more water and changed another 30 %. I didn't feed the animal for two days and I'm happy to report all is fine.

My point is that even if there isn't uneaten food in the system, natural waste from a big meal can over whelm a tank that is probably too small. Next stop she displaces a stomatopod from a 125 gal system.

Thanks, Roy! It's great to get firsthand accounts of how this works, since there are often so many "rule of thumb" and "anecdotal evidence" discussions about this sort of thing.

And of course, I'm glad to hear the rubscens recovered, of course! They're great little octos!
I had a similar circumstance when I fed my cuttlefish fiddler crabs instead of shore shrimp. I got the fiddler crabs to give the cuttlefish a varied diet, but they were about 5 times the size of their normal food. The next day, the water parameters spiked and I ended up doing a 30% water change to return the tank to normal. No more fiddlers for the cuttles...
Roy, Cuttlegirl
Is it the amount of food or is the substitute food richer than their normal fare? That is, if we give a variety would it be prudent to change the quantity according to something like the fat content? Right now I am just trying to get Trapper to eat anything. He may have eaten a mithrax (supplied intentionally) but I expect to go to fiddlers and hopefully frozen shrimp/scallops. I suspect the frozen shirmp would be much richer than the crabs so if my hunch is right, smaller amounts would be prudent but the scallops are not as rich as the shrimp ...
Nice Roy, I recently had my octo "overeat" but it's small, and the tank is very mature. I was just talking about you to my mom about how your mantis shrimp stabbed that blue ring between the eyes.
I really don't know the answer to the question about the quality of food. In both cases, the food was shrimp, the typical food being live grass shrimp and the new food tiger prawns. My guess is that the real problem was the amount. The tiger prawn was ingested in minutes. Unfortunately, it was also digested and excreted quite quickly as well.

We got more grass shrimp today, but she only gets one a day from now on.

I guess we're really lucky here, we have fed our Pinnoctopus cordiformis 10-15 large (10-15cm carapace width) NZ Cancer crabs (Cancer novaezelandiae) without water quality issues but I must emphasise ALL our tanks are large (>200L), extremely stable (been running many years!) and most importantly open (ie not recirc) tanks. The waste doesn't build up. In addition they are siphoned and debris removed every day! But in a closed system or even in ours if we don't siphon every day you get nasty gunge and anoxic bits at the bottom :yuck: I guess you can't get round the housekeeping!


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