Injured Banggai Cardinalfish

[LOZReefer]

I started my 150g last March. The two cardinalfish were the first two fish to be in the tank. One of them has always been a little aggressive to the other but nothing I had to worry about - very insignificant.

Here recently, it has gotten more aggressive and both of their fins are a little tore up - I attempted to catch one of them and put it in the QT before it got worse but was unsuccessful and just hoped they would work it out. He showed no sign of injury last night, this morning I looked in the tank and the aggressive Banggai has a bulged eye and his left side larger (ventral/pelvic?) fin is tucked in and he can't swim all that great.

I think something got ahold of him but I'm really not sure. I'm assuming he will likely not make it but I was able to catch him while lights were still off and threw him in my QT system just in case. I don't plan to medicate but if it doesn't improve after a couple days, I may put him in a true separate QT and medicate.

The yellow tang can sometimes be territorial especially as lights turn down and he starts to head to his safe space to sleep but he usually just runs them off, I've never seen him actually attack anything. I've also got a decent sized emerald crab (I feel like if this got ahold of him, he would definitely be much worse, if not gone).

I did have a Tailspot Blenny randomly die a month or two ago (I think maybe it got too close to the the Yellow Tang's home during the night and it got him and might be responsible for the injured Banggai).

Note: The injured one in these pictures is the more aggressive one. The less aggressive one is uninjured.

Tank:
150g
Started in March 2025
All params in check

Livestock:
2x Banggai Cardinalfish
2x Designer Clowns
1x Yellow Tang
1x Blue Hippo
1x Melanurus Wrasse
1x Royal Gramma

CUC:
Hermits
Nassarius
Trochus
Cerith
Cleaner Shrimp
2x Emerald Crab

 

[vetteguy53081]

I started my 150g last March. The two cardinalfish were the first two fish to be in the tank. One of them has always been a little aggressive to the other but nothing I had to worry about - very insignificant.

Here recently, it has gotten more aggressive and both of their fins are a little tore up - I attempted to catch one of them and put it in the QT before it got worse but was unsuccessful and just hoped they would work it out. He showed no sign of injury last night, this morning I looked in the tank and the aggressive Banggai has a bulged eye and his left side larger (ventral/pelvic?) fin is tucked in and he can't swim all that great.

I think something got ahold of him but I'm really not sure. I'm assuming he will likely not make it but I was able to catch him while lights were still off and threw him in my QT system just in case. I don't plan to medicate but if it doesn't improve after a couple days, I may put him in a true separate QT and medicate.

The yellow tang can sometimes be territorial especially as lights turn down and he starts to head to his safe space to sleep but he usually just runs them off, I've never seen him actually attack anything. I've also got a decent sized emerald crab (I feel like if this got ahold of him, he would definitely be much worse, if not gone).

I did have a Tailspot Blenny randomly die a month or two ago (I think maybe it got too close to the the Yellow Tang's home during the night and it got him and might be responsible for the injured Banggai).

Tank:
150g
Started in March 2025
All params in check

Livestock:
2x Banggai Cardinalfish
2x Designer Clowns
1x Yellow Tang
1x Blue Hippo
1x Melanurus Wrasse
1x Royal Gramma

CUC:
Hermits
Nassarius
Trochus
Cerith
Cleaner Shrimp
2x Emerald Crab

These fish can be aggressive towards each other and best in odd numbers, 1-3-5 and so forth and even then, often left is one. Isolation here is key but even then the behavior may not change once they are reunited

 

[LOZReefer]

These fish can be aggressive towards each other and best in odd numbers, 1-3-5 and so forth and even then, often left is one. Isolation here is key but even then the behavior may not change once they are reunited

Yeah, I had planned on rehoming it if it pulls through

 

[vetteguy53081]

Yeah, I had planned on rehoming it if it pulls through

If its swimming in a spiral pattern, its in physical trouble with low chance of recovery

 

[LOZReefer]

If its swimming in a spiral pattern, its in physical trouble with low chance of recovery

It can swim with purpose. It didn't have any issues evading my net when I was trying to catch it, it just doesn't hold it's position like normal cardinalfish - where they kind of just sit motionless in the water column, he kind of has to bob around if that makes any sense. But he can move around okay, it's just not a normal movement.

Here is a video.

 

[vetteguy53081]

It can swim with purpose. It didn't have any issues evading my net when I was trying to catch it, it just doesn't hold it's position like normal cardinalfish - where they kind of just sit motionless in the water column, he kind of has to bob around if that makes any sense. But he can move around okay, it's just not a normal movement.

Here is a video.

This may be a sign of declining health

 

[Jay Hemdal Verified Community Expert]

It can swim with purpose. It didn't have any issues evading my net when I was trying to catch it, it just doesn't hold it's position like normal cardinalfish - where they kind of just sit motionless in the water column, he kind of has to bob around if that makes any sense. But he can move around okay, it's just not a normal movement.

Here is a video.

With one eye involved, that usually indicates an injury (other issues would involve both eyes). The bobbing in the video could be due to gas behind the eye, causing the fish to float more on that side. Normally, fish can overcome that slight buoyancy issue, but this fish may be weakened overall, and not able to hold its position normally. Those eye gas problems are slow to heal (some never do) - once the gas comes out of solution it just doesn't go away easily. Nobody really knows why gas builds up like that after an eye injury, but it likely has something to do with damage to the capillaries.

Let us know if it is still trying to feed tomorrow - that may indicate how serious this is for the fish.

Sorry I don't have any treatment to offer you.....there isn't any infection involved (yet), so medications won't have any benefit.

 

[LOZReefer]

With one eye involved, that usually indicates an injury (other issues would involve both eyes). The bobbing in the video could be due to gas behind the eye, causing the fish to float more on that side. Normally, fish can overcome that slight buoyancy issue, but this fish may be weakened overall, and not able to hold its position normally. Those eye gas problems are slow to heal (some never do) - once the gas comes out of solution it just doesn't go away easily. Nobody really knows why gas builds up like that after an eye injury, but it likely has something to do with damage to the capillaries.

Let us know if it is still trying to feed tomorrow - that may indicate how serious this is for the fish.

Sorry I don't have any treatment to offer you.....there isn't any infection involved (yet), so medications won't have any benefit.

This makes perfect sense. It seems exactly like there is gas buildup behind his eye causing the issue with buoyancy/swimming. Poor guy, hopefully he makes it through but at the end of the day, he was the one starting all the problems so....

 

[Jay Hemdal Verified Community Expert]

This makes perfect sense. It seems exactly like there is gas buildup behind his eye causing the issue with buoyancy/swimming. Poor guy, hopefully he makes it through but at the end of the day, he was the one starting all the problems so....

That is the one odd thing here - it is usually the LOSER that ends up with the damage. However, in some cases the damage can come from aggressive attacking, or the weaker fish getting a lucky attack in at some point.