Here’s a detailed guide to determining the gender of betta fish, compiled from advice from multiple highly credible sources:
1. Comparison of Physical Characteristics
Fin Shape
Males: Dorsal, anal, and caudal fins are long and broad (up to 2–3 times the body height), spreading like a fan when extended.
Females: All fins are short (approximately equal to the body height), and the tip of the pelvic fin often has a thread-like structure (except for round-tailed bettas).
Color Differences
Males: Boast vivid colors (highly saturated hues like red, blue, or green) with complex patterns and clear boundaries.
Females: Have duller colors (mainly gray, brown, or light yellow) with simple, blurry patterns.
Abdominal Features
Females: The abdomen is rounded and swollen, with a small white-yellow circular "belly button" (ovipositor) at the front, which becomes more prominent during the breeding season.
Males: The abdomen is flat and lacks a protruding genital pore.
2. Behavioral Observations
Aggression Test
Males: Will display aggressive behavior toward a mirror (flaring gills, spreading fins).
Females: React more mildly, occasionally flaring gills but showing no intense aggression.
Breeding Season Behavior
Males: Build bubble nests, chase females frequently, and develop more vibrant colors.
Females: Swim in a zigzag pattern, with a swollen, drooping abdomen.
3. Special Identification Techniques
Flashlight Illumination Method: Shining a light through a female’s abdomen reveals a long, strip-like ovarian structure.
Lip Thickness: Males have thicker lips (adapted for fighting).
Age Influence: Gender characteristics are not obvious in juvenile fish (<2 months old) and become clearer with development.
4. Common Misconceptions to Note
Short-Finned Varieties: For example, Plakat bettas—males may also have short fins, so other characteristics should be considered together.
Color Exceptions: Some artificially bred females may also have bright colors.
By cross-verifying multiple characteristics, you can accurately determine a betta’s gender. If you’re still unsure, it’s advisable to compare multiple individuals of the same breed to observe differences.