This post is more than three years old so may contain incorrect information, or opinions I no longer hold.

The Battle Of The Oscar Fish Tank

03 May 2020 | ~7 minute read

I have multiple fish tanks, but I've been having real problems with my largest tank lately. I think I've finally solved the problems, but let's talk about The Battle of the Oscar Fish Tank.

So if you don't know, an Oscar is a South American cichlid (pronounced “sick-lid”). They are very large fish, growing to around 18″ in the wild and up to 14″ in captivity. Like many cichlids, they can also be very aggressive and territorial.

Oscar fish are also very messy, so they need to be in large tanks. Otherwise your nitrogen cycle will be a mess and you could kill the fish.

I had 2 of them in my 400 litre (approx 100 US gal) system. The big guy, Dice (on the left of the picture), was about 13 inches long, and the smaller female, Betty, is around 10 inches.

These two are a mating pair. They have been together since they were fry and generally get on well. There are some arguments between them, but Betty generally holds her own.

One day I came into my study to find Betty looking like this:


Look at her f**king face! It's a mess. When I got in, Dice was puffing his gills out and shaking his body (a sure sign of aggression in Oscars). They'd had a massive fight and Dice wasn't done yet - he just kept coming at poor Betty.

Splitting The Oscar Fish

The only option I really had was to split Betty & Dice up. Problem is, I don't have another tank big enough for a big Oscar. One of them had to go.

I called my local fish store (LFS) and they said they would take one of them. But which one? I was in a real conundrum here. On the one hand, Betty has the best personality - she's quite timid, but she's friendly. Dice, to be honest, is just a bully and a dick. But he's a gorgeous Oscar specimen.

Decision decisions.

I ended up removing Dice from the tank. My rationale being that I had more chance of introducing other fish with Betty. Plus, she had been badly beaten up, so the additional stress of moving her may have killed her.

It was a tough, heart wrenching decision; and I don't mind telling you, I cried over a fish! Oscars are often called the dogs of the fish world. They're intelligent and really bond with their owner. So giving up Dice was awful.

Anyway, he went to my LFS and he's very happy there. I know they will look after him and after lock-down ends, I can't wait to go see the big fella.

We're Not Done Yet!

Oh no, the saga of the Oscar fish continues. So Betty is in a bad way and I'm really worried I'm going to lose her. Her face is mangled, she has developed hole in the head; she's in shit state.

On top of all the injuries, I've split her and her life-long mate up. This is bad.

A week goes by and her face is starting to heal, but she hasn't eaten a thing. Two weeks, still no eating. Three weeks, still nothing. Fish can go weeks without eating, but three weeks is pushing it.

At this point, her face was pretty much healed, and her hole in the head was also healing nicely. It was the lack of eating that had me concerned at this point - was she going to starve to death?

Double shit.

I've been keeping all different kinds for a few years now, so I like to think I know what I'm doing. But after three weeks of no eating, and with no sense of Betty's hunger strike ending anytime soon, I was out of ideas.

I got in touch with Andy from my LFS, Somefin Fishy, to see if he had any ideas. The best he could come up with was to add more fish. This is something I had considered, but I wasn't sure Betty was ready.

Adding fish may seem strange to some of you, but being on her own in the tank, Betty may have thought other fish were hiding because a larger predator than her was around.

The behaviour for being concerned about predators is usually a lack of eating, and a reluctance to come out into the open parts of the tank. That's the behaviour I was seeing, so I thought it was worth a shot.

Adding New Fish

Like I said, Oscar fish can be aggressive and territorial, so I had to choose the fish to go in with her carefully. As much as I wanted to, I couldn't add another cichlid, as she would probably get bullied. I could have added a young one potentially, but if it fit in her mouth, there was a high chance of her eating it.

Cichlids were out.

I needed something that grew to a descent size and was very passive. Then Andy recommend Silver Dollars. They grow to around the size of a saucer and are super placid - exactly what I need.

I'd considered Silver Dollars myself, but they've never really been a fish that has interested me, so I was a little reluctant. At this point I had to put Betty's needs before my desire to have the best looking fish in there, so Silver Dollars it was.

Silver Dollars are also a schooling fish, so I had to buy a few. With a lot of trepidation, I added five Silver Dollars to Betty's tank. Not knowing how she would react, I was very nervous. She inspected them, but she didn't puff up and there was absolutely no aggression.


I turned the lights off and left the dollars to settle in for a few days. Still no aggression seen and Betty seemed to be coming out of her shell. Nice, time to feed them, I thought.

Silver Dollars are a herbivorous member of the Piranha family, but they will eat pretty much anything you put in the tank. And they sure did - vegetables, blood worms, brine shrimp, algae wafers - everything. They wolfed the lot down.

Betty still didn't eat. 🙁

Triple shit.

So earlier this week, I took a last ditched attempt to get Betty eating - I decided to starve the entire tank all week.

My idea being that she was just being a spoilt brat, and by starving the whole tank, I'd create more competition for food and hopefully she would eat.

So on Monday the whole tank went on a forced hunger strike. I've been keeping a close eye on the tank all week - everyone seems happy enough - albeit hungry - with no deaths or fights. That's a good sign.

It's Saturday 02nd May 2020 as I write this and this morning I came in to check on everyone. I walked up to the tank and Betty started wagging her tail fin; told you they were like dogs! She hadn't done that since Dice had left.

Let's try a feed...

Oscar fish feed from the surface. What she had been doing over the last few weeks, is retreating to the bottom of the tank whenever I took the lid off.

Not this time! This time she swam up to top, ready to feed. Could it be? Is the old Betty back?

I reached for her food and there she remained, at the top, ready to scoff whatever I gave her. I threw in half a dozen pellets and WOOF! They went in a second. She scoffed the lot in one go.

Sweet relief!

Better yet, as she chomped down on the pellets, waste came out of her gills, which the dollars loved grazing on!

The dollars needed a proper feed as well though, so I threw in a few algae/spirulina wafers - Betty at them too!

“She's definitely back.” I thought.

Eventually she left some wafers for the dollars to scoff down on, and everyone seems very happy in the tank. Here's Betty now, with her hole in the head healing up, along with one of my dollars with a wafer in her gob.


Woah. It's certainly been a rough few weeks in the Oscar fish tank! Keeping cichlids can be very difficult, but it's so worth it in my opinion.

You know what? I actually really like the Silver Dollars now. I didn't give them a fair chance. They're a gorgeous fish and they're full of character, I'm so happy with how the tank has turned out. Great recommendation from Andy, there.

Yes, I had to get rid of poor Dice, which I'm still gutted about. But it was the best thing to do for Betty's sake. Plus, I know Andy will either look after him, or find him a good home.

Let's hope the Zen in my Oscar tank continues. If it doesn't, I'll be sure to write an update.

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