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Creating an octopus den with PVC pipe?


Blue Ring
Jul 12, 2019
Hello all!

I have two research projects where I'd be sampling octopuses at sea (and then release them) as well as to keep mothers in the pots and transfer them to the aquaculture facility to study them.

For these to happen, that means I'd need to create my own octopus pots, or a den for them to naturally go into so that I can retrieve them (rather than a trap that would harm them). These pots would then be on the seabed for a month or so. What I can find at the local store is this T-junction PVC pipe. I like that it has a threaded cap on top so that I can potentially remove the cap and transfer out eggs (the life stage that I'll be focussing on for my research) to another aquarium. I will also be sealing one end on the side using a push-on cap and seal it with a cyanoacrylate gel (or Superglue gel).

I'd also like to paint them black for two reasons: 1) to reduce the risk of theft by reducing its visibility and more importantly, 2) to hopefully make it a more ideal den choice for octopuses since white is technically more conspicuous and a black one may be more visibly hidden on the seabed.

Here are my doubts and questions:
1) Has anyone used octopus-safe/aquarium-safe/ocean-safe paint? A lil digging on the Internet gave me two options: Krylon Fusion paint for plastics and Performix's Plasti Dip paint but it'd be good if anyone who has actually tested this to let me know if it's indeed safe specifically for octopuses. (Source: Best aquarium safe paint for inside and outside your tank)

2) Has anyone used the cyanoacrylate gel in octopus tanks? I know that silicone glue is toxic to octopuses but I'm not sure about cyanoacrylate.

3) For those who had octopuses that laid eggs in an artificial den, did they lay on top or on the sides? As no one has studied the species I'm looking at, I can only hope that they'd lay the eggs on the top cap rather than the one on the side since that'd have been sealed.

4) You guys are the experts, I have not had octopuses in tanks before and it's been a year (and counting) that I'm planning this aquarium set-up to ensure the best welfare possible for the octopus. So I'd greatly appreciate if anyone could point out anything you think are not ideal or even harmful to these awesome animals.

Thank you for reading!

PS: FYI I have also checked the sizes and they're good for the species that I'm studying.

Hello! The dens you have showed a photo of seem like they could work well. Hopefully I can help with some of your questions.

1- I don't know much about aquarium paint, but I would be sure to wait the entire week of cure time that the krylon paint recommends, maybe even a few days longer if you can afford. Once finished, I would soak your pvc pieces in DI or RO water over night or maybe even for two nights just to be sure.

2- the cyanoacrylate gel is probably your best bet for glue. I have used it before on octopus dens and other cephalopod dens without any trouble. Just make sure to let the glue cure fully before cleaning and soaking the dens in DI or RO water (which you should do with each den you make).

3- I cant guarantee where the eggs will be laid, and most likely they will be laid in a different part of every den. Anecdotally I can say they often lay their eggs on the wall furthest from the opening, often near the top of the den. Realistically, I wouldn't expect to be able to remove the eggs from the den without dismantling it, so depending on what and how you want to remove the eggs, you may need to brainstorm a different den design.

4- I can give you tips and advice on your aquarium setup if you can share some photos of the system.

Lastly, I have a few questions for you!
1- What species are you working with?
2- Are they a large or small-egg species?
3- What are you planning on doing with the eggs after they have been laid? (this will help me give better suggestions as to den design to improve egg accessibility.)
4- How many dens do you plan to make? How long will you leave them in the water? I assume you know the breeding cycle of the animal and can plan to put the dens out at the appropriate time of year?
Wow thank you so much for this precious advice!! :octorun: I'll make sure to add in those important steps before using them.

Aquarium Setup:
So I potentially have two different facilities (the only choice I have actually) for the mothers and for the eggs. - For the mothers I'll be placing them in outdoor mesocosms where each mother will be placed in a 1000L tank; it looks something like this. I'm thinking of attaching astroturf to the inner walls of the tank as well as a mesh net over the tank. Considering that I'll have to check if the mother and eggs are doing well, I guess I'll be attaching ropes to the den to slowly pull it up since the tank's gonna be deep. Note also that these are dens that I'm putting out at sea and then transporting them to the tank facility without removing them from the dens to reduce stress and also because eggs would have already been laid.

- As for the eggs, below is an image of the potential set-up. They are 25L tanks (~20L of water) which I'll be using to study the effects of climate change. Basically I need to combine eggs from different mothers to have a total of at least 50 eggs in each tank and it seems like my only choice here is to sew each egg to say a styrofoam piece using a nylon thread. It'll be tedious and I hope it won't stress the embryos too much but it's the only method I've come across in the scientific literature.

Both these mother and egg set-ups are using a flow-through seawater system with UV and 0.05um filtration. One thing I'll need to note for the setup below is to maybe put the heater and the drainage outlet in a mesh bag and seal up the opening at the corner of the glass tank where the wires go through.

These are responses to your questions:

1) and 2) It's the Octopus berrima, a large-egged species (1-1.4cm length). It was last studied in 1980 by RW Tait and it's very difficult to access the paper. But there're some extracted information and photos in this link from page 355-361. You can see there's a photo of the eggs laid singly on an oyster shell but I'm not sure if they really laid them in that orientation or were they somehow moved for the photo, since most species would have them hanging. My colleague who recently sampled them did find their eggs on the vertical end of a similar pipe (a regular cylindrical pipe without the top outlet), something like how we hang stuff on our walls instead of the ceiling.

3) After the mothers lay >50-100 eggs, I'll need to transfer the eggs to the smaller tanks all the way until they hatch.

4) For Research Project #1, I'll have 120 dens that I'll be soaking at sea for about a month. The same dens will then be used again for Research Project #2, where I'll ultimately need only 10 dens with mother octopuses which transferred to the 1000L tanks until they die naturally. Yep we do we have an idea when is the best time to put them out.

Thank you sooo much for your kind offer to help!:vampyro:
Thanks for the photos and more detailed information! I have some additional advice.

1- AstroTurf and a net over the top of those outdoor tanks seems like a good strategy to me. Depending on the water level in the tanks you may not need the astroturf but its always better to be safe than sorry.

2- For the eggs, have you thought about using forceps to remove them from the surface they were laid on and then floating them in a mesh basket or a plastic colander? I have had success with this strategy in the past. I've never had to sew the removed eggs back onto some other surface, but maybe the case is different for this species. I can give more specific information about basket design/flow over the eggs if you would like.

3- The heater and the triangular opening at the back end of the tank will definitely need to be contained in a better way than what is shown in your photo. A mesh bag might work but I would really suggest adding a piece of perf-plate to the back side of the tank to keep the heater away from the octopus (this also solves the problem of the opening at the back end of the tank for the wires). I strongly recommend against letting your animals have access to a heater (even if it is contained in a mesh bag)- it can only end up causing you problems. I can send you some diagrams or give material recommendations if you have more questions.

All in all it sounds like a cool experimental design! I hope you can manage to get some animals and end up with mothers on eggs!
Yay so relieved to know the design is feasible!

1) Great!! Plus I'd assume mothers wouldn't have the tendency to escape but yes perhaps it's better to be safe than sorry, can also prevent land animals from sneaking in I guess! For these 1000L tanks, do you reckon it's essential to add sand, rocks and other critters? My financial constraints for these projects are actually very very tight, but if they're very important for the octopus I'll try my very best to obtain them somehow. Also, do I take it that the original T-junction pipe could serve as a good den and also for my purposes? I was thinking even if they don't lay eggs on the top cap, perhaps I could also lift it to access the back for the eggs.

2) Omgosh you're a genius! It's an incredibly smart idea!!! :eek2::eek2::eek2: Yes please I'd love to know more an optimal design. Do you use soft forceps, or is the stalk strong enough for hard forceps? The potential hiccup I could think of right now is that, because I'd need to sample a few eggs once in a while throughout the experiment, I'd imagine that things would get messy the moment I move the colander upwards since they're not secured. So I found this item that doesn't have the walls of a usual colander and so allow me to go under and grab an egg out, plus the radial design can also let me keep track of their exact ID (like which mum they came from), but this item might be too large for the small tanks and I'd also need to find a way to make it float.?

3) Yes I agree!! I actually raised that problem to the staff of the facility but I couldn't quite convince them when I said it's not good for them to access it; they said the heater is made of titanium and wouldn't harm the octopus. Is there something I could say to counter that? I'd love to know your recommendations! I'm having a look at some acrylic sheets and am asking to see if they can drill <2mm holes (I've a feeling they're gonna cost a lot). Just an idea - perhaps I could somehow rest the flat colander that I linked above on this acrylic sheet, and hold the other corners with some bamboo sticks?

Thank you so much for your extremely valuable advice so far!! :biggrin2::biggrin2:

1- I would recommend adding some rocks or different hides/dens to the 1000L tanks if possible, but you don't need to go crazy- especially if budget is an issue. Are you planning on having more than one octo per tank? That may prove to be problematic depending on how much aquascaping you are able to do.

2- You have a few options to make an egg cradle. I've done it out of mesh before, where I cut it into a shape that could be folded into a "tray" for the eggs (I'll attach a mediocre MS Paint drawing at the bottom of this reply) and used the same coral frag glue we were talking about earlier in the thread to secure the corners together. Finally, you can attack a suction cup by cutting a small hole in one of the "walls" of the egg cradle and gluing a suction cup to the wall so that the egg cradle can be secured to the wall of the tank, near where the flow is entering the tank. Secondly, depending on the tools you have at your disposal, you could use some perf plate (that I mentioned in an earlier reply) and do a similar technique where you cut the plate into a few different panels and glue them together using the coral frag glue. You can attach a suction cup the same way for this design also, allowing you to mount the egg cradle on thew all of the tank. This way, your egg basket will be easy to access and you wont have to worry about the eggs rolling around or falling out of the cradle. (I'll include a photo) You could even build dividers or multiple different egg cradles to keep track of your individual clutches.

3- It's not about the metal in the heater that I am worried about, its the heat that the heater puts off which will be your problem. The water temperature immediately surrounding the heater is quite a few degrees higher than the set point on the heater itself, and the dissipation of the heat through the system cools it down to an appropriate temperature for the animal. Octopuses are inherently curious creatures and will try to grab and play with the heater. If the octopus has access to the heater they could hurt themselves by grabbing onto the heater and burning themselves, they could manage to move the dial and change the temperature in their enclosure, they could tug on the heater cord and mange to pull it out of the wall and leave the tank without heat- there are many ways this could go wrong. If the employees at the research institute have experience with octos they should know better than to allow the animal to have access to *any* tank element that could cause damage to the animal. This includes filters, pumps, heaters, cables, drains, and basically anything other than rocks, sand, and maybe some plants. I would reinforce the fact that you can't have your animals dying during the middle of your research, and dividing the tank to keep the non octopus-friendly items in a separate area is paramount to the comfort and health of your animals.

On amazon you can buy perforated plastic sheets (these may be available through other distributors as well) which you can cut to fit in your individual tanks. You can also use this material to create an egg cradle.

Here is a photo of an egg cradle I've made from perf plate, and also here is a photo of a template you can use to cut some plastic mesh and fold/glue it into shape- its a bit less sturdy but also cheaper and easier to make.


On a side note- How are the tanks set up specifically? Its a bit hard to tell in your photo which side is the input and which side is the drain on the tanks.
-Is the heater next to the drain or next to where the water comes in?
-Is the water treated in any way before it enters the tank aside from UV and mechanical filtration?
-What temperature is the water that enters the tank and what temperature do you plan to keep the animals at?
Thank you!!

1) Sure I should have extra dens/pipes to place around, I can check for rocks as well. Nope! Only one octopus per tank.

2) Wow that's an ingenious design! Thank you for sending it through. I have some questions:
A) What egg sizes have you used this basket for previously?
B) Will the eggs be floating naturally? I helped a colleague with his cuttlefish eggs experiment before and they would certainly fall to the bottom if not secured
C) Since eggs for my study species are 4-5mm wide only when mature, I'm afraid they may be small enough to go through the perforations at earlier stages. What do you think of glueing the stalk to the inner side of the hole?
D) Is there a recommended distance between the eggs and the bubbling from the air pump?

3) Completely agree with you! I'll definitely convey that to them, thank you so much for providing the details.

Tank set-up

- There's a thin black pipe running right above the tanks, those feed directly into each tank through the back of the tank, then drains out through the front of the tank (shown in orange). So the heater (in blue) is next to where water comes in. Also for the drainage outlet, there is a removable cover (in purple), this should make more space for the eggs as it should likely be cordoned off as well using the perforated plate?

- Nope only UV and 0.5uM filtration (sorry I said 0.05 previously). The staff said they normally do a dripping rate of 4L/hour for 14h for this kind of flow-through seawater system.

- It fluctuates a lot even within the same season, but I'll be starting them in March/April when temperatures should be about 16-19 deg Celsius. For controls I'd keep them at about 18deg. Other climate change simulated conditions would be 21degrees and 23 degrees although I'll still have to finalize this when I manage to get more thermal data from this year's records.
Hi qiazopus! I am just popping in here to say that your setup looks great and your project sounds really interesting, but also to suggest that if you need access to older papers on cephalopods and you are having trouble finding them, send an email to the FASTMOLL listserve with the full Tait 1980 citation. The community there is excellent at sharing older papers.

- I have previously used this basked for bimaculoides eggs, it worked quite well. I imagine if your eggs are small in diameter you could probably find perforated plastic with holes smaller than the diameter of your eggs, or you could buy some plastic mesh material and build the basket using the diagram I posted in my earlier reply.

- The eggs are a bit less than buoyant. They will sink given time but are a bit "floaty". Resting them in this cradle should be no problem unless you have really high flow or aeration in the tank.

- I would recommend against gluing the eggs to the basket. I suppose it might work but it sounds incredibly tedious and the chemicals in the glue could damage the fragile egg casing. It would be much preferred to make a mesh basket if you feel the eggs are to small to go in a basket made of perforated plastic, rather than having the plastic basket with eggs glued to it.

- If you are planning to aerate the eggs, I would have the air stone far enough under the basket so that the eggs aren't getting knocked up and out of it by the air stone, probably something like 6-8" depending on how much air you are using (you probably don't need to use much) I can send a video of what I would anticipate proper air flow to be if you'd like.

- I would make sure you have bricks to put on top of the tank lids, or a way to seclude the animal from having access to the opening in the top of the tank.

The staff said they normally do a dripping rate of 4L/hour for 14h for this kind of flow-through seawater system.
I'm a bit confused by this, is the flow through the tank not continuous?
Oh dear I think I might be a bit confused here as to where you actually place the eggs and keep them in place, especially since they may not completely sink or float.

So I came up with this poorly drawn diagram. Supposed the shaded area in red on the inside of the basket is Surface Y, are the eggs floating up against Y (i.e. egg stalks in contact with Y like in Picture B), or are the eggs resting on Y (i.e. bottom of egg in contact with Y like Picture C), or are the eggs actually outside of the basket resting on it like in Picture A?

If it's like in Picture B, wouldn't the eggs risk sinking to the bottom of the tank? And if it's like in Picture C, wouldn't they also risk floating about?

Yes a video would be very helpful and much appreciated! Do you happen to still have photos of the bimac eggs with the basket?

The flow of the tank can actually be adjusted so I will be able to make it continuous if I want to. Hopefully that would help with removing the nitrogenous wastes as well.
I think you may be overthinking it a bit. Here is a photo of the basket in action (my apologies for the blurry photo) the eggs rest in the bottom of the basket (these are squid eggs so they are a bit rounder than octo eggs but they have the same buoyancy. The eggs settle to the bottom of the basket with no issues, so I think it is set up the same as your diagram C. When I stage octopus eggs in a basket like this I just set them in the basket. Often they are laying on their sides or on top of other eggs, this has never been a problem for me.

I can send a video of proper aeration in a few days when I am back in the lab. Please let me know if this helps clear things up and if you have other questions!

Also, I would highly recommend continuous flow through the tanks if possible. Any updates on the dividers for the heaters and the cables in the tanks?

Awesome this definitely cleared things up for me! Thank you so much, can’t be more grateful for your advice.

I’ll definitely be finding a way to compartmentalize the devices to separate them from the octopuses, most likely a plastic mesh divider. I’ll also make sure the water flow is continuous :smile:

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