Why Are My Tetra Fish Chasing Each Other

Your fish are actually fighting for survival

I just dropped my heavy work boots by the door after ten grueling hours dealing with flooded canister filters at the shop, and I am entirely out of patience. My phone is blowing up with people sending me blurry videos of their new community tank, frantically asking why are my tetra fish chasing each other around the plastic castle. You bought cute little colorful fish and expected them to hold hands and sing songs.

Nature does not work like that. Tetras are technically characins, an incredibly active family of schooling fish that establish brutal dominance hierarchies in the water. When you just throw three of them into a glass box, you force them into a terrifying underwater arena.

They nip fins. They claim territories. They absolutely will bully a weaker fish until it dies from sheer exhaustion and stress.

The Huge Mistake I Made With Skirt Tetras

Back in October 2018, I thought I was an absolute genius when I bought exactly three stunning white skirt tetras for my twenty-gallon planted setup. It was a cold, rainy Tuesday night and I hastily dumped them in before going to sleep. I woke up the next morning to find two of them relentlessly torturing the third one, pinning him behind the glass heater until his tail was completely shredded.

I felt like a massive idiot sitting there in my pajamas, drinking cold coffee, watching my poor fish suffer because I was too cheap to buy a proper school. Numbers matter. A lot.

If you do not have at least six of them in a group, you will constantly be wondering why are my tetra fish chasing each other to death. A large group spreads out the natural aggression so nobody takes the brunt of the abuse.

Here is an opinion that always makes the corporate pet store managers furiously angry at me. Selling tetras in groups of two or three should be legally banned. It is basically a guaranteed death sentence for the weakest fish in that plastic bag.

Knowing When It Is Actually About Sex

Sometimes the chasing is not about murder. It is about reproduction. Male tetras will relentlessly pursue females when they are trying to spawn, darting through the water like tiny, colorful torpedoes.

You need to look closely at who is doing the chasing. Males are usually much slimmer and sometimes more vibrantly colored, while females get thick, round bellies full of eggs. If a skinny fish is constantly nudging the belly of a fat fish, he wants to mate.

The problem is that a relentless male can still exhaust a female to death. She needs dense floating plants or a massive clump of java moss to hide in when she is tired. If your tank looks like an empty parking lot, you have completely failed your pets.

Why Are My Tetra Fish Chasing Each Other During Feeding Time

Food makes everybody completely crazy. If you only drop one tiny pinch of flakes into the exact same corner every morning, you create a microscopic war zone. The biggest, meanest tetra will claim that spot and brutally attack anyone who comes near his breakfast.

You have to scatter the food across the entire surface of the water. Make them work for it. If you need some decent quality pellets that don’t dissolve into mush immediately, Check out our fish care supplies here.

Aggression is totally natural in a community tank, but you have to manage the environment. You need visual barriers. Plants, driftwood, and rocks break up the sight lines so the dominant fish cannot see every single corner of the tank at once.

If a bully cannot physically see the submissive fish, he stops chasing it. According to evolutionary biology, schooling fish rely heavily on visual cues to coordinate their movements and establish rank Wikipedia/Shoaling and schooling. Give the victims somewhere dark to hide.

They Smell Weakness Instantly

Fish are ruthless opportunists. If one of your tetras gets sick or injured, the rest of the school will often turn on it immediately. It is a harsh survival mechanism to drive disease away from the healthy school.

If you see one fish getting picked on and it has white spots or fuzzy patches on its skin, you have a massive problem. This is a huge reason why are my tetra fish chasing each other in established tanks. You have to remove the sick fish and put it in a hospital tank right now.

Do not leave a wounded fish in the main display. The healthy fish will literally peck its eyes out. Disgusting but true.

Your Tank Is Just Too Small

People constantly message me asking why are my tetra fish chasing each other, and then they send a picture of six active fish crammed into a five-gallon desktop cube. That is a prison cell. Tetras need lateral swimming space to burn off their chaotic energy.

If they cannot swim in long, straight lines, they get frustrated and take it out on their tankmates. You need a twenty-gallon long tank minimum for most of these species. Anything smaller is just a recipe for shredded fins and dead pets.

If you are staring at your aquarium right now asking why are my tetra fish chasing each other, you have to break the cycle. Sometimes you just have a psycho fish. You need to rearrange the entire tank to destroy the established territories.

Right now, I want you to walk over to your tank and count your tetras. If you have less than six of the exact same species, grab your keys and drive to the local fish shop to buy more before they close. Your weakest fish will not survive another night of being hunted alone.