The short answer
A newly added fish hiding is almost always completely normal. A new tank is a strange, exposed place, and most fish retreat to cover for the first few days — sometimes a week or two — while they settle in. The best response is patience: give it cover, keep the tank calm, and make sure the water is right.
Settling in takes time
Being moved and released into new surroundings is stressful for any fish, so hiding is a healthy survival instinct, not a fault. Gentle acclimation softens the shock, and a tank with plenty of plants, wood, rocks and caves actually helps a new fish grow bolder, because it knows it has somewhere safe to retreat. Keep the lights modest and avoid tapping the glass or crowding the tank while it adjusts.
Help it feel at home
- Provide hiding spots — plants and decor make fish feel secure, so they venture out more.
- Watch quietly at feeding time — a new fish that comes out to eat is settling in well.
- Keep the water stable — new tanks can spike ammonia, so test and do a water change if needed, and make sure the tank is cycled.
- Check the tankmates — an existing fish chasing the newcomer will keep it hidden; see why is my fish chasing other fish?.
When to look closer
Give it time, but keep watching. If a new fish stays hidden well beyond a couple of weeks, refuses all food, or shows other signs — laboured breathing, clamped fins, pale colour — then move from patience to investigation. Compare with why is my fish hiding all the time? and how do I know if my fish is sick?. For anything that worsens, ask an experienced fishkeeping community or an aquatic vet.