How To Select Fish For Aquarium

Buying fish is a complete headache.

I just spent four agonizing hours scrubbing hard green algae off fifty different glass display tanks at the shop, my arms are completely soaked with cold water, and my patience is entirely gone. People constantly email me demanding to know how to select fish for aquarium setups without accidentally bringing home a total disaster.

It happens every single day of the week. You confidently walk into the local pet shop with your wallet ready to spend cash. The glowing fluorescent lights and softly bubbling water filters completely mesmerize you.

You point excitedly at the brightest, flashiest fish in the tank and blindly demand the teenager with the dripping net bag it up. Then it predictably eats all your other fish. Heartbreaking.

Stop guessing how to select fish for aquarium setups

Beginners always walk into the store completely blind. They have absolutely no logical plan before staring at the glass. This is exactly how you end up with a terrifying, aggressive monster that outgrows your tiny glass box in three short weeks.

You really need to thoroughly research the true adult size of the animal before you even look at a green net. That cute, shiny little silver dollar you just bought is rapidly going to grow to the heavy, thick size of a dinner plate. Fact.

The absolute worst mistake I made in 2012

Let me tell you about a rainy Saturday afternoon back when I naively thought I knew absolutely everything about what I was doing. I saw this tiny, adorable baby Oscar fish swimming playfully in a dealer’s bare tank, and I bought him on the spot for my peaceful 10-gallon community living room setup. I felt incredibly stupid and horribly guilty three days later when I woke up to find he had systematically hunted and swallowed every single expensive neon tetra I owned.

He was just acting on his natural, unapologetic predatory instincts. I was the complete idiot who didn’t bother to read a single fish care book. Never impulse buy a living creature just because it looks small and helpless right now.

Look at the whole tank

When you are slowly figuring out how to select fish for aquarium living, you have to aggressively stare at everyone in the dealer’s tank. If one single fish in that specific water looks sick, the water is already heavily contaminated with microscopic nightmares. Pass.

Look closely for clear eyes, bright vibrant colors, and smooth unbroken scales. The fins should be completely intact and not clamped tightly against their frightened sides in a weird defensive posture. Healthy fish swim actively around the middle of the water column and don’t just sulk miserably in a dark, dirty corner of the glass.

If they look like they are gasping desperately at the surface, walk away immediately. That means their delicate gills are severely damaged by invisible parasites or the water is completely toxic with high ammonia levels. Bad news.

My highly unpopular opinion about chain stores

Here is a brutal truth that usually makes corporate retail managers want to aggressively punch me in the face. You should absolutely never trust the advice of a random teenager working the fish aisle at a giant retail chain pet store. Most of them have literally zero training in aquatic biology and will happily sell you five highly aggressive cichlids to put in a tiny, unheated bowl with a peaceful, coldwater goldfish.

They just want to make a quick, painless sale and go on their scheduled lunch break. Find a dedicated, independent local fish store where the grumpy owner actually breeds rare fish in their own damp basement. Trust me.

Compatibility is literally a matter of life and death

Fish are fiercely aggressive, wildly territorial, and unapologetically brutal to each other. When thinking deeply about how to select fish for aquarium communities, you have to match their individual temperaments perfectly. Do not lazily mix shy, peaceful shoaling tetras with massive, angry cichlids.

Some fish naturally school together in massive, synchronized groups for safety against hungry predators. The neon tetra is a classic example of a species from the family Characidae that requires a large group to feel secure and prevent severe, life-threatening stress Wikipedia/Characidae. If you buy just one isolated tetra, it will literally die of loneliness and paralyzing fear.

You also desperately need to match their specific water chemistry preferences exactly. You cannot dump soft-water Amazon fish in a tank full of hard-water African rift lake limestone rocks. It completely destroys their fragile kidneys over time.

Watch them eat before you buy anything

Always politely ask the store employee to sprinkle some dry flake food in the water. This is the ultimate, undeniable test when deciding how to select fish for aquarium life. A healthy, robust fish will aggressively attack the floating food the exact second it hits the surface tension.

If a fish totally ignores the food and just stares blankly at the dirty glass, something is horribly wrong internally. It might be highly stressed, carrying a massive internal parasite load, or completely traumatized by the brutal international shipping process. Do not ever buy a starving fish.

It will probably just die in your hospital tank anyway. Speaking of which, you definitely need a proper, cycled hospital setup running in your house to isolate new arrivals. If you need some reliable basics to get started immediately, Check out our fish care supplies here.

Size actually matters in this hobby

I am so incredibly tired of telling stubborn people that fish do not simply grow to the size of their confined tank. That is a toxic, completely ridiculous myth propagated by lazy salespeople trying to move inventory. Their bodies keep desperately growing while their internal organs crush violently against each other in a small space, eventually causing a slow, agonizing death.

Know your exact tank volume. A good, basic baseline is one inch of adult fish per gallon of water, but that rule breaks down incredibly fast with bulky, messy fish like heavy-bodied fancy goldfish. Messy.

You strictly need to know exactly how to select fish for aquarium dimensions before you even leave your driveway. Research. Do not rely on dumb luck.

Bringing them home safely

Once you actually successfully navigate how to select fish for aquarium survival, you have to get them home safely without accidentally killing them in the car. Float the tightly sealed plastic transport bag in your dark tank for at least twenty long minutes. This equalizes the varying temperature incredibly slowly so your new pets don’t instantly go into severe thermal shock.

Never dump the filthy, pathogen-filled store water directly into your pristine, perfectly balanced tank. Net the fish out of the plastic bag very gently.

I really need to go sit down right now. My knees hurt terribly and I smell strongly like rotting fish food. Good luck at the store.