Japanese Eel Tank - Help

[Okesa]

Hello! I have a bit of a strange request, and given how informative the Aquarium Co-Op YouTube channel and website are, I thought I would see if the forum could give me some advice.

I work in a school in Japan, and over the last 6 months have been working on upgrading the neglected fish and turtle tanks at the school. The last creature left that needs a life upgrade is the school's pet eel. It is a Japanese freshwater eel (unagi) who was gifted to the school around 5-ish years ago after the students took a field trip to an eel restaurant. From what I have been told, there were originally 2 eels, but the other one died (possibly was eaten by this one?).

Because these eels are not commonly kept as pets, there isn't really much information available online about tank setups. It is currently in a tank that will hold a max of about 17 gallons (but is only actually filled up to around 12.5 gallons) with sand for substrate, a tube to hide in, and a bubbler. There is also filter, but it is broken. I know that this is way too small, as most recommendations I can find online for other eel species say you should use anywhere from a 30 to 50 gallon tank. From what I have read, eels prefer slow moving water, so I was looking at getting a large sponge filter, but I have also read that eels are messy and might need something more powerful. Most places also recommend a tank heater, but I'm not sure if unagi are quite as tropical as most species normally kept as pets. 

Basically, if anyone can give me any kind of recommendations for filtration, if a heater is necessary or not, tank mates that are the least likely to be eaten (even if fish are all not ok, some kind of snails or something to act as a cleanup crew would probably be a good idea), etc. Una-chan (the eel) and I would really appreciate it. 

[Keeg]

I would say a big bubble filter with a strong air pump or power head should be good. And unagi can be found from Japan to Vietnam so their water temp really varies. If yours has been doing fine without one for half a decade now, I would assume it wouldn't need one now.* Eels are pretty slow so anything with streamline bodies like tetras can do fine. But with the water temp (would be great if you could give an estimated number) you can be fairly limited. I would go with snails as a clean up crew, lots of people hate them but hey, the eel shouldn't/ probably won't eat them. 

*They like 25-29 C on average, I would go with around 26 because they like the fresh water rivers and breed with warmer temps. Assuming you want to control the temp with a heater or not*

With a max size of 40 cm, I would say the ideal home is 55 g (200 liter) or more, but you can get away with a 30g (120)ish long tank with a tight lid on both.  

Thats the absolute perfect name for an eel, I (and probably lots of others on this site) would love to see some pictures of Una-chan. 

Extra tip: When I try to find info on animals that are usually meant as food like fugu or trout, its way easier to look at the farming requirements rather than aquarium hobby specifics.  

 

[Okesa]

Thank you for the tips. The school, like most Japanese buildings, only has heating (and cooling) in the classrooms, and the tank is located in a hallway.The water temp is currently probably around 25°C, based on the temps of the other aquariums, but it doesn't have a thermometer currently. Now that I think about it, there might be an extra one from when I cleaned out a storage area. I'll have to put that in the tank tomorrow. 

Based on what I remember from last winter when I was working on the turtle upgrade, the water temp can get as cold as around 15°C (Don't worry - the turtle didn't move into the tank until it had a heater and a filter and a basking area with UV and heat. He had previously been living in a rectangular plastic box without even enough water to cover his shell entirely, while the 65 gallon tank I moved him to sat there with one fish in it).

I'm hoping to convince the school to buy a 65 gallon tank identical to what the turtle is in, but between the tank and a stand big enough to hold it, it will be kind of expensive. I found a much more budget friendly 35 gallon tank that is a backup option if the 65 is more than they are willing to spend. 

I don't have any pictures of Una-chan on my phone, but I'll try to get some tomorrow. The kids just picked the name the other day - up until now, it had been nameless, like all the other fish and the turtle. Thankfully they almost all have names now! I've made introduction posters and fact sheets for all the tanks, and it's really helped to get the kids more interested. Until I can get some eel pictures, here's the introduction poster, and a bonus picture of Jimmy the Turtle chillin. 

[Okesa]

On 9/8/2021 at 6:25 PM, Keeg said:

I would say a big bubble filter with a strong air pump or power head should be good. 

By bubble filter, what exactly do you mean? Something like this?

Or something like this?

[Keeg]

On 9/8/2021 at 3:09 AM, Okesa said:

By bubble filter, what exactly do you mean?

I talk about these when I say bubble filter but what you sent technically are the same thing. You can add a pump to the tube and make it stronger without risking fish safety too, though its a sponge filter at that point. Its all interchangeable in my mind. 

 

Edited September 8, 2021 by Keeg

[Okesa]

On 9/8/2021 at 7:17 PM, Keeg said:

I talk about these when I say bubble filter but what you sent technically are the same thing. 

 

Perfect! I already have a big one of those that a co-worker bought for a project but it turned out to be too big for what they needed. I just need to get an air pump for it - does something around 2 watts seem powerful enough for a 65 gallon?

[Keeg]

I dont know much about wattage, plug it in, if it makes a strong flow of bubbles, it's good. 

this image from google shows a good example

[sudofish]

Good on you for trying to give it a better life. I'm impressed that it was in a school hallway. I can imagine how horribly that would go with American schoolkids.

[Okesa]

The kids mostly leave the animals alone unless it's their turn to feed them. The tank upgrades have made everyone much more interested/invested in their respective occupants, so I'm hoping now that the eel has a name I can convince the school to spend some money based on the success of everything so far. 

[Okesa]

As promised, here is Una-chan. 

I did some digging and found a thermometer, so I went ahead and put that in the tank. Last I saw it was just under 25°C. I also found an air pump rated for a 60cm aquarium (which is the length of the current setup) that appears to be in working order, and I have a sponge filter that a co-worker didn't need any more, so I'm going to get some air tubing tonight after work and will hopefully have some filtration going by tomorrow. Fingers crossed that this is the first step of a much bigger upgrade. 

[Keeg]

Thats one freaking adorable eel. 10/10 wish they were more in aquariums and not on plates 

[Okesa]

It's usually hiding in its tube - I think this is the first time I've ever seen it move and look alert.

[Kilrkitty08]

You are doing such a great thing for these animals but also for the school.  I hope a lot of young students catch the fish/eel keeping bug from admiring your hard work and dedication!  

"Heroes Don't Always Wear Capes"  

[Okesa]

Update:

Last Friday I added a sponge filter and tested the water parameters. The Nitrate was off the charts, so I changed about 75% of the water. I came in today and did another parameter check - the level is still high, but it did seem to have gone down some. (It's a little hard to see the difference in the photo, but it was much less dark today than it was last week.)

I did a 50% water change and added some water plants to hopefully use up the excess nitrate. I also got a cutting off of the pothos in the nurses' room that I'm rooting and planning to add to the tank as soon as possible. Any other suggestions for lowering the nitrate?

[eatyourpeas]

Beautiful eel, @Okesa!

The floating plants (they look like Elodea sp.) will be helping with removing ammonia, but getting the pothos in as soon as you can will help with the nitrates. You can add the photos to the tank directly and not wait for it to root outside.

Edited September 13, 2021 by eatyourpeas

[Okesa]

@eatyourpeas the Japanese teachers have just called it 水草, which translates to "water weed." Elodea definitely looks like what it is! It seems to grow pretty well in all of the tanks except the one with the turtle, because he eats it all. 

I'll have to take my cutting down to the tank this afternoon to try to see if I can figure out a way to secure it.

[eatyourpeas]

I am assuming Una-Chan has a lid on the tank, and pothos likes to be emersed, so you can just start by putting the cutting with the stem in the water and the leaves outside the tank, using the lid to keep it in place. Try to use the same gap that the airline tubing is coming through.

[Okesa]

The pothos is in! Hopefully all the nitrate helps it grow well. 

[Okesa]

Checked the water quality again, and while the nitrates are still high, they are slowly falling.

I did another partial water change - this is either the 4th or 5th. I had hoped the water changes would be making a more dramatic difference. Is nitrate something that can hang around in the substrate? The bottom of the tank has around 2 inches of sand. I know for a fact that the tank was without a working filter (and I'm pretty sure was just having water periodically added, but not changed) for at least a year and a half, but more than likely a lot longer than that. 

In slightly better news, we have a new leaf on the pothos, and it is also starting to send some more roots down! Hopefully it will help to improve the water quality a lot. 

I also made a cute poster explaining the nitrogen cycle, because if we are going to have fish tanks in the school they might as well be educational!

[Keeg]

"cute p

On 9/21/2021 at 1:33 AM, Okesa said:

I also made a cute poster 

This aint just a "cute poster", this is a whole work of art. 15/10 😍

[Okesa]

@Keegthe illustrations are from a Japanese website that makes free clip art. I just photoshopped them all together and added the text. (thank you for the nice compliment, though. 🙂)

I've actually made posters of all the fish introducing themselves and fact sheets that are on the walls next to the tanks. 

[Okesa]

Update:

We just did a walkthrough to see the progress of the renovations on the building we are moving into at the end of March. I found a spot in the entranceway that is long enough for both the turtle tank and an upgraded tank for the eel, and close to a big sink for cleaning/water changes. The vice principal is having the construction workers add an electrical outlet on that wall (there weren't any).

Haven't received official budget approval yet, but hopefully I will be putting together a new home for Una-chan in the next few months!