What to Do When Your Fish Arrive (Step-by-Step)

Your new aquarium fish have arrived — this is the moment everything comes together.

But this is also where many problems begin.

Not because the fish were shipped incorrectly, but because the first 30–60 minutes after arrival are often rushed or misunderstood.

👉 How you handle fish immediately after delivery has a direct impact on their survival, stress level, and long-term health.

This guide walks you through exactly what to do — and why each step matters.

Before You Open the Box

It’s tempting to open everything immediately, but take a moment.

Make sure:

If your tank isn’t ready, stop here.

👉 New fish should never be introduced into an unprepared system (see How to Cycle a Fish Tank (Step-by-Step Guide)).

Step 1: Open the Package Carefully

When you open the box:

  • Remove the bags gently
  • Avoid sudden movement or shaking
  • Keep the room calm and quiet

At this stage, fish may look:

  • Pale
  • Less active
  • Still

This is normal after transport.

Step 2: Check the Condition of the Fish

Before doing anything else, take a quick look.

Healthy aquarium fish should:

  • Be upright
  • Show some movement
  • Respond slightly to light

Do not panic if they seem quiet — fish often slow down during shipping.

If you’re unsure what to look for, review How to Choose Healthy Aquarium Fish Before Buying to understand normal vs concerning signs.

Step 3: Float the Bags (Temperature Matching)

Place the sealed bags into your aquarium and leave them to float for:

👉 15–20 minutes

Why this matters:

Fish are extremely sensitive to temperature changes.
Even a small difference can cause shock.

Floating allows the water inside the bag to match your tank.

Step 4: Gradually Adjust Water Conditions

After temperature is matched:

  • Open the bag
  • Add small amounts of aquarium water
  • Wait a few minutes between each addition

Repeat this over 20–30 minutes.

This step helps fish adjust to:

Skipping this is one of the biggest causes of stress in new fish (see Signs of Stress in Aquarium Fish).

Step 5: Add Fish to the Aquarium (Without Bag Water)

When ready:

👉 Gently transfer the fish using a net
👉 Do NOT pour bag water into your tank

Why?

  • Bag water may contain waste
  • It can introduce unwanted bacteria
  • It may affect water quality

Step 6: Keep the Tank Calm

Once fish are in:

  • Keep aquarium lights off for a few hours
  • Avoid tapping the glass
  • Minimise movement around the tank

This allows fish to settle naturally.

If fish hide, don’t worry — this is expected (see Why Are My Fish Hiding?).

Step 7: Do NOT Feed Immediately

Wait at least:

👉 Several hours (or until the next day)

Why?

  • Fish are often too stressed to eat
  • Uneaten food creates waste
  • Water quality can drop quickly

If feeding seems unusual later, check Fish Not Eating – What It Means and What to Do.

The First 24 Hours (What to Watch For)

This is the most important period.

Observe:

  • Breathing rate
  • Swimming behaviour
  • Interaction with other fish

Normal behaviour includes:

  • Hiding
  • Reduced movement
  • Slow adjustment

The First Few Days

Over the next 2–3 days:

  • Fish should become more active
  • Feeding behaviour should improve
  • Confidence should increase

If problems appear, they are usually linked to:

  • Stress
  • Water conditions
  • Compatibility

How New Fish Affect Your Aquarium

Adding new fish changes your tank immediately.

More fish means:

  • More waste
  • Increased biological load
  • Greater pressure on filtration

This is why you should always:

Common Mistakes After Fish Arrive

These cause most problems:

  • Adding aquarium fish straight into the tank without acclimation
  • Pouring bag water into the aquarium
  • Turning aquarium lights on immediately
  • Feeding too soon
  • Adding too many fish at once

Each of these increases stress and risk.

A Better Way to Think About It

This process isn’t about “getting fish into the tank quickly.”

👉 It’s about giving fish the smoothest possible transition.

Less shock = less stress = healthier fish.

Final Thoughts

The moment your fish arrive is one of the most important stages in fishkeeping.

Handled correctly, fish settle quickly, adapt well, and become part of a stable, healthy aquarium.

Handled poorly, even healthy fish can struggle.

Take your time, follow the steps, and let the fish adjust at their own pace.

If you’re planning your next additions, you can explore buy aquarium fish, browse tropical fish, or check available live fish for sale to find species that suit your setup.