How to choose healthy aquarium fish: What to look for before you buy

Buying fish for your aquarium is exciting, but choosing the healthiest ones is far more important than picking the brightest colours.

In a pet shop, every tank looks lively and every fish appears healthy at first glance. Yet the difference between a fish that thrives for years and one that dies within days is often decided before it ever leaves the store.

Here’s what to look for before bringing home your next aquatic pet.

Start by checking the pet shop

Healthy fish usually come from healthy systems, so assess the shop before focusing on individual fish.

Look for:

• Crystal-clear water in most tanks. A small amount of algae is normal, but cloudy, murky or yellow water is a warning sign.
• Clearly labelled tanks with species names and basic care information. This often reflects knowledgeable staff and good husbandry.
• No dead fish floating in tanks or trapped against filters. An isolated loss can happen, but multiple dead fish should raise concerns.
• Separate quarantine or “not for sale” tanks where new or sick fish are isolated from healthy stock.

Scan the whole tank first

Before choosing a single fish, spend 30 seconds watching the entire tank.

Many fish diseases spread quickly, so the health of neighbouring fish matters just as much as the one you want to buy.

Avoid tanks where several fish are:

• Clamping their fins tightly against their bodies.
• Hiding continuously.
• Scratching themselves against rocks or decorations.
• Gasping at the water’s surface.

Healthy tanks contain fish that are active, swimming normally and exploring their surroundings.

What does a healthy fish look like?

A quick head-to-tail inspection reveals a lot about a fish’s condition.

Eyes

Healthy fish have bright, clear and symmetrical eyes.

Avoid fish with:

• Cloudy eyes.
• Bulging eyes.
• Sunken eyes.

Fins

Fins should be fully open and undamaged.

Watch out for:

• Torn or frayed fins.
• Clamped fins.
• Fins that remain folded against the body.

For example, a healthy betta displays its fins proudly rather than keeping them tightly closed.

Body and scales

Healthy fish have smooth bodies with intact scales.

Avoid fish showing:

• White spots resembling grains of salt.
• Gold or dusty patches.
• Cotton-like growths.
• Red streaks.
• Raised lumps.
• Sunken or pinched stomachs.

White spots are often a sign of Ich, one of the most common aquarium diseases.

Gills

Breathing should be slow and steady.

Avoid fish that:

• Breathe rapidly.
• Gasp continuously.
• Hold their gill covers permanently flared open.

Healthy behaviour is the biggest clue

A healthy fish behaves differently from a stressed or sick one.

Look for fish that:

• Swim smoothly without wobbling or listing to one side.
• Respond when people approach the tank.
• School naturally if they’re species such as tetras or rasboras.
• Eat eagerly when food is offered.

If possible, ask the staff to feed the fish before you buy them.

Bottom-dwelling species such as corydoras and plecos should rest upright and actively forage around the aquarium rather than lying on their sides.

Four questions to ask before buying

A reputable aquarium shop should happily answer these questions.

1. How long have these fish been in the shop?

Ideally, fish should have been in the store for at least seven to 14 days after arriving. Fresh imports are often still stressed from transport.

2. What are the water parameters?

Ask about the pH and temperature, then compare them with your own aquarium to minimise stress during acclimatisation.

3. What food are they eating?

Knowing their current diet makes it easier to transition them once they arrive in your aquarium.

4. Can you test my aquarium water?

Many reputable aquarium stores offer free water testing. Bringing a sample from your home aquarium helps ensure your water is suitable before introducing new fish.

Take your time

The healthiest fish are not always the brightest or most colourful.

Spending a few extra minutes observing the aquarium, asking questions and checking the condition of both the fish and the store dramatically increases the chances of bringing home healthy pets that will thrive for years.

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