Below is a detailed guide to identifying the gender of guppies, based on key physical and behavioral traits:
1. Body Shape Comparison
Male Guppies
Slender, streamlined body; adult size ranges from 3–4 cm (1.2–1.6 inches)
Tail fin makes up a large portion of the body (about 2/3 of total length)
Female Guppies
Round, plump body with a swollen abdomen
Larger than males: adult size is 5–8 cm (2–3.2 inches), over 1/3 bigger than adult males
2. Color and Patterns
Male Guppies
Bright, vivid colors (red, blue, yellow, etc.)
Intricate patterns on the tail fin and dorsal fin
Unique tail fin shapes in special varieties (e.g., lyretail, swordtail guppies)
Female Guppies
Dull, single colors (mostly silver-gray or pale yellow)
Simple patterns on the tail fin with no obvious bright hues
3. Key Body Part Differences
Anal Fin (Under the Abdomen)
Males: Thin, rod-shaped (this is the gonopodium, a modified fin used for reproduction)
Females: Broad, fan-shaped
Gravid Spot (Female-Only Trait)
A dark (black) or orange spot near the anus
Becomes more noticeable during the breeding period
4. Behavioral Differences
Males
Often chase females
Swim quickly to display their tail fins (a mating behavior)
Females
Move slowly
May hide when their abdomen is swollen (a sign of carrying fry)
5. Tips for Identifying Juvenile Guppies
Under 1 month old: Hard to distinguish; focus on the shape of the anal fin
2+ months old: Males start developing bright colors, and their anal fins become thin and rod-like
Summary
Male Guppies: Slender body + bright colors + thin, rod-shaped anal fin
Female Guppies: Round/plump body + dull colors + broad, fan-shaped anal fin + gravid spot
Note: Some albino female guppies may lack a visible gravid spot. In such cases, use other traits (body shape, anal fin) to confirm gender.