Aggressive Zebra Danios

Hi,

I have a 15 gallon Fluval Flex tank that had 7 whiteclouds in it at first, then I decided to add in 6 Zebra Danios and 6 Glowlight Danios 5 days ago. The newly added Zebra Danios, being the largest ones in the tank, become aggressive and start chasing, fin nipping all other fish, they at each other.

I'm not sure what is causing this kind of aggression because I know all of these are peaceful, community fish. Any suggestion would be great.

Some additional info on the tank:
- Temperature is around 18°C to 20°C with no heater (since they are all cold water fish, I don't even bother using a heater).
- Water flow is relatively strong, I'm using this pump instead of the original pump that came with the tank. (The fish seem to be more active and eat a lot more when I increase the water flow).
- The tank is fed once a day using an automatic fish feeder with this
- The light is on from 11 a.m to 7 p.m, I added this to increase lighting (not sure if this is important).

Also, I would like to say that I'm just a beginner with relatively low budget to spend( but I do know about the nitrogen circle and the tank is 100% cycled). I know that adding live plant will give more hiding space but I cannot afford that right now, but still I would love to hear suggestion on some good beginner plants that requires no substrate( I'm thinking of adding java moss since they are really affordable and easy to take care of).

 

That's a really beautiful hardscape design!!!

To answer your question, I am going to assume that it's more of a pecking order where the aggressive danio is trying to establish who's boss. However, if this continues to escalate for a few days or a week, then I would remove the danio out of the tank.

Good beginner plants that requires zero substrate are anubias, java fern, bucephalandra, and floating plants (hornwort, duckweed, salvinia, etc.).

 

Also anacharis is one of my faves and hornwort

 

You have 18 fish in a 15 gallon tank. They're probably cramped and are frustrated. Sometimes passive fish can become aggressive when there's not enough space and will bully other fish to the point that another fish dies (could be from not getting food or from exhaustion from being chased). The tank was fine with just the minnows. If you want to keep some of them, keep one school but not both. I'd say return both schools and if you still want more fish, buy 3 more minnows and be done.

Your tank is pretty btw.

 

That's a really beautiful hardscape design!!!

To answer your question, I am going to assume that it's more of a pecking order where the aggressive danio is trying to establish who's boss. However, if this continues to escalate for a few days or a week, then I would remove the danio out of the tank.

Good beginner plants that requires zero substrate are anubias, java fern, bucephalandra, and floating plants (hornwort, duckweed, salvinia, etc.).

Thank you. It's true that the fish seem to be less aggressive as time goes by.
And as for the plants, I might go with Anubias when I have the budget for it (they cost like 50$ at my local fish store and they look really nice since they come with a piece of driftwood as well). Any floating plant is just not gonna work because the flow in this tank is quite high and will push the plant around lol.

 

Also anacharis is one of my faves and hornwort

Thank you for the great suggestion!

 

You have 18 fish in a 15 gallon tank. They're probably cramped and are frustrated. Sometimes passive fish can become aggressive when there's not enough space and will bully other fish to the point that another fish dies (could be from not getting food or from exhaustion from being chased). The tank was fine with just the minnows. If you want to keep some of them, keep one school but not both. I'd say return both schools and if you still want more fish, buy 3 more minnows and be done.

Your tank is pretty btw.

Thank you. It is true that the tank is quite small. I can't really return them because the fish store doesn't have a return policy. But since all the fish seem to be much less aggressive now and the tank has enough bio media to support all these fish, I'll give them a try before considering taking them out.

 

Thank you. It's true that the fish seem to be less aggressive as time goes by.
And as for the plants, I might go with Anubias when I have the budget for it (they cost like 50$ at my local fish store and they look really nice since they come with a piece of driftwood as well). Any floating plant is just not gonna work because the flow in this tank is quite high and will push the plant around lol.

$50 for anubias?!

 

$50 for anubias?!

Yeah, they don't have the small one, only the huge one that grow on a piece of driftwood so 50$ is not that unreasonable. It's something similar to this but better.

 

Yeah. $50 for an anubias is just way too high, especially if it's on a driftwood.

 

Yeah. $50 for an anubias is just way too high, especially if it's on a driftwood.

Oh I forgot to mention that it's 50$ Canadian though, so it's like 37$ US. But yeah the price is no doubt very high but that's just how it is in Canada( the Zebra Danios that I bought are 4.99$ each LOL).

 

Oh I forgot to mention that it's 50$ Canadian though, so it's like 37$ US. But yeah the price is no doubt very high but that's just how it is in Canada( the Zebra Danios that I bought are 4.99$ each LOL).

Ah okay. That makes total sense.