When you walk into a fish shop, your eyes go to the big, flowing Delta tails. They look like underwater curtains. Then you see the Round Tail guppies. They look small. They look “Kampung.”
But let me tell you a secret: The Round Tail is the 4×4 Truck of the guppy world. While the Delta Tail is a Ferrari that breaks down if it hits a bump, the Round Tail is built to survive anything.
Here is the deep breakdown of why this shape matters.
1. The Physics: The “Zero Drag” Advantage
Fish swim by pushing water with their tail (caudal fin).
- Delta Tail: It’s like swimming while wearing a wedding dress. The huge surface area creates massive Drag. The fish has to wiggle its entire body just to move forward. This burns energy fast.
- Round Tail: It’s a paddle. It is short, stiff, and hydrodynamic.
The Result:
- A Round Tail guppy can swim against a current.
- It can out-swim a hungry Tiger Barb.
- It rarely dies of “exhaustion” or stress during shipping.
2. The Health Shield: No Nips, No Rot
The number one killer of fancy guppies is Fin Rot. Fin Rot usually starts at the edges of the tail where blood flow is weakest.
- Long Tails: The blood has to travel very far to reach the tip of a giant Delta tail. This makes the edges weak and prone to rotting or tearing.
- Round Tails: The tail is short and close to the body. Blood circulation is perfect.
The “Nip” Factor: Aggressive tank mates (like Tetras or Bettas) target long, flowing fins. They see a Delta tail as a toy. They ignore Round Tails because there is nothing “dangling” to bite.
3. The “Breeder’s Secret”: The Crossing Tool
You might wonder, “If they are so good, why don’t shops sell more of them?” Actually, professional breeders keep tanks full of them in the back.
Breeders use Round Tail males to fix weak strains. If a strain of “Full Red Deltas” becomes too inbred and weak, the breeder will cross them with a Short/Round Tail male. This injects “Wild Vigor” (strength) back into the bloodline, making the babies stronger while keeping the red color.
4. Best Setup for Round Tails
Because they are elite swimmers, you can put them in tanks where normal guppies would die:
- Planted Tanks with CO2: These tanks usually have high flow to move the CO2 around. A Round Tail loves the current.
- Outdoor Ponds: If a dragonfly nymph or a cat tries to catch them, a Round Tail is fast enough to escape. A Delta Tail is a sitting duck.
- Community Tanks: You can keep them with Angel Fish or Gouramis because they are too fast to be bullied.
The “Short Tail” Variations
In the hobby, “Round Tail” is the general category, but you will see it sold under these names:
- Round Tail: A perfect circle.
- Spear Tail: Round but with a tiny point (like a leaf).
- Cofer Tail: Like a shovel.
They all share the same “Short Tail” benefits.
The Shop Guy’s Take
If you are a beginner and you are tired of your expensive guppies dying after 2 weeks, stop buying the “Big Tails.” Look for the Round Tails (often labeled as “Wild Type,” “Endler Hybrid,” or just “Short Tail”).
They might not cover the whole tank with color, but they will be zipping around your tank alive and happy long after the fancy ones have faded away.
