Red-bellied piranha bitten by others! What now?

[GermanPiranhaLover]

Hi everyone, I am new in this forum, but I really need your help. I have 6 red-bellied piranhas in a 720-liter freshwater tank. Four of them I got "second-hand" when they were already a few years old, they are now about 25 cm long. I added two smaller piranhas less than a year ago, those are now 15 cm. They all got on well together.
A few weeks ago, though, one of the smaller ones injured himself on his head. Even though the scratches healed quite well, he started to behave different, excluding himself from the shoal. His left eye also protruded a bit.
Now the shoal has attacked him and bit a part out of his belly (picture). We isolated him and got the vet to examine him. The vet found Plesiomonas shigelloides. We don't know what to do now. Placing him back into the tank is not possible (we tried that before, he instantly got attacked again). Could the bacteria be the reason for the attack? What would you do?

Here is more information:
720Liter tank
JBL Test Lab: nitrate 40 mg/L; pH 7.0-7.1; nitrite 0.05 mg/L; phosphate 40 mg/L; total hardness 4-7°; ammonia <0.05 mg/L;
aquarium is running for about 10 months
6 red-bellied piranhas, 17 Crossocheilus oblongus, 2 red bruno, shrimps, snails (Planorbarius corneus)
quarantine for all new fish
temperature 25 degree Celsius
live plants: Vallisneria, anubia barteri
Filter: Fluval FX6
some natural sunlight, mostly neon tube T5 (one), lights on for 2 pm-10 pm
changing water every week (about 1/4th to 1/3rd)
food: defrozen smelts, shrimps, conch meat, once to twice a week.

Thank you so much for your help in advance!
Brigitte (I am from Germany)

 

[tlindsey]

Hi everyone, I am new in this forum, but I really need your help. I have 6 red-bellied piranhas in a 720-liter freshwater tank. Four of them I got "second-hand" when they were already a few years old, they are now about 25 cm long. I added two smaller piranhas less than a year ago, those are now 15 cm. They all got on well together.
A few weeks ago, though, one of the smaller ones injured himself on his head. Even though the scratches healed quite well, he started to behave different, excluding himself from the shoal. His left eye also protruded a bit.
Now the shoal has attacked him and bit a part out of his belly (picture). We isolated him and got the vet to examine him. The vet found Plesiomonas shigelloides. We don't know what to do now. Placing him back into the tank is not possible (we tried that before, he instantly got attacked again). Could the bacteria be the reason for the attack? What would you do?

Here is more information:
720Liter tank
JBL Test Lab: nitrate 40 mg/L; pH 7.0-7.1; nitrite 0.05 mg/L; phosphate 40 mg/L; total hardness 4-7°; ammonia <0.05 mg/L;
aquarium is running for about 10 months
6 red-bellied piranhas, 17 Crossocheilus oblongus, 2 red bruno, shrimps, snails (Planorbarius corneus)
quarantine for all new fish
temperature 25 degree Celsius
live plants: Vallisneria, anubia barteri
Filter: Fluval FX6
some natural sunlight, mostly neon tube T5 (one), lights on for 2 pm-10 pm
changing water every week (about 1/4th to 1/3rd)
food: defrozen smelts, shrimps, conch meat, once to twice a week.

Thank you so much for your help in advance!
Brigitte (I am from Germany)

View attachment 1291740

Instinctively some fish species will attack sick or the weakest among the group. Tbh would isolate if it is infected.

 

[tlindsey]

Instinctively some fish species will attack sick or the weakest among the group. Tbh would isolate if it is infected.

Welcome aboard

 

[kno4te]

My guess is being smaller it got picked on and was tagged. Once weak and stressed the other p’s were just doing what they normally do in the wild.

I believe the bacteria took hold of a weak and stressed fish.

Would keep it separate and beef it up till atleast the same size as the other piranhas and reintroduce. Try keeping some plants and decor to take away lines of sight and direct paths.

Just my suggestion.

 

[GermanPiranhaLover]

Thank you so much! What do you think about putting a plastic wall with smaller holes in the tank and keep the injured piranha apart from the others this way? He might like that better than a separate tank for months to come?

 

[kno4te]

Thank you so much! What do you think about putting a plastic wall with smaller holes in the tank and keep the injured piranha apart from the others this way? He might like that better than a separate tank for months to come?

That’s fine to do as well.