The signs
A big catfish short of vitamin B1 refuses food, for weeks or months. Then it loses its balance: it lists, turns belly up, or swims upside down as if it does not know which way is up. It is easy to mistake for an infection.
The cause
Some foods contain thiaminase, an enzyme that destroys vitamin B1. Herring, anchovy, smelt, minnows and carp have it, and so do shrimp and mussels. Freezing does not kill it. A redtail fed mostly on these runs short of B1 even when it eats well.
The fix
A vet can inject vitamin B1, thiamine. The balance problem can stop almost at once; appetite takes longer, often weeks, sometimes a second shot. Then change the diet to fish without thiaminase, such as mullet, cod, pollock and flounder, soaked in a vitamin supplement with B1.
What to take from it
- Vary the fish If you feed whole fish or fillet, do not rely on one kind, especially herring or smelt.
- Ask about B1 If a big catfish stops eating or loses balance, tell your vet what it has been eating.
- Be patient Recovery takes weeks to months. Adults can fast for a long time and come back.