Thank you for trying to help your cousin's pacu. Pacu are not fish that every one can keep. Pacu get VERY large - red belly pacu can get up to 36" and black pacu up to 48". They are long lived fish with potential to live 30+ years if kept in the right way. They can also die very young if kept in poor conditions, i.e., poor water parameters. Pacu are charcins and have that characin skittishness - it doesn't take anything to spook them, and they will swim frantically away from an imaginary predator - slamming into tank walls, tank lids and any decoration in the tank until a final vicious slam into something brings them back to reality. I am convinced that pacu can break tanks. As big as they are, my pacu slam into tank walls and tank lids so hard, that it sounds like an explosion.
Pacu are more sensitive to nitrogen products than many of their counterparts in the wild. The tank must be cycled, i.e., have enough beneficial bacteria in the filtration system to consume all the ammonia generated by fish respiration, fish waste, and food waste. While a lot of fish keepers aim at keeping nitrates at 20 ppm or less, I have found that keeping nitrates less than 5 ppm keep my pacu looking their best.
If your cousin is serious about keeping his pacu, he needs to be aware of the following:
- Pacu should live a long time. Plan for a 30 year commitment to the fish
- Pacu get VERY large. Plan on large housing for the fish
- Pacu spook very easily, so remove everything from the tank that they can break or injure themselves on
- Pacu need good water parameters to thrive. Get a fresh water master test kit and test the water for ammonia, nitrite and nitrates. Do enough water changes to keep the nitrates low, even if it is daily multiple water changes. If the tank is cycled, there will not be any ammonia or nitrite.
Our pacu have been family members for 18 years now. They are wonderful personable fish who are very curious about the world inside and outside of their tank. They have beautiful grins.