Poorly fish?

Question

i think one of my neon tetra fish is sick... it doesn't eat, and keeps opening and shutting its mouth very quickly. it's still swimming around but looks like its lost or dazed.

anyone know whats wrong with it?

Answer 1

check water parameters but if all other fish are fine its prob an infection.

look for white spot, i find that fish will stop feeding and have laboured breathing before the spots actually appear. may dart about and rub on hard surfaces too.

it may be in shock if its a newly introduced fish.

Answer 2

What are your parameters?  do a 35% water change, could be suffocating, is there enough water flow to give oxygen to the water?