How to tell whether your betta (fighting fish) is male or female?
Once a fighting fish has reached sexual differentiation, you can tell whether you're fighting fish is male or female by a number of characteristics.
1) Length and shape of anal finFemales generally have shorter anal fins and shorter tails in general. This is especially true for the longer fin variety where the males go on to develop longer whereas the female betta fins stay relatively short.
2) Presence of an egg spot, ovaries visible on cellophane type bettas and breeding stripes
The egg spot, also known as the ovipositor is generally visible in sexually mature females.
Figure 1: ovipositor and breeding stripes on a female betta:
Figure 2: Cellophane betta with visible ovaries
3 Length and thickness of ventral fins
Males: long and thick ventral fins
Females: shorter and thinner ventral fins
4) Body thickness
Females: wider body especially towards the head
4) Bubble nest
Blowing of bubble nests by male bettas: Betta fish have an organ called a labyrinth organ which allows the betta fish to inhale air and create bubbles to form a bubble nest. These bubbles are coated with the betta's saliva which helps keep the form of the bubbles. The masterpiece of a completed bubble nest aims to entice a female betta over to mate. She will judge him on his finnage, size, colouring (with red reported to be the colour female bettas are most likely to mate with), and bubble nest before she decides whether or not to mate with him.
It has been observed that some females bettas do blow bubble nests and help in the construction during mating. However, this is the exception rather than the norm.
Male betta fish are known to be territorial and will flare their gills when faced with a threat. The intention is to make themselves appear bigger, intimidating and showing dominance. This is where the betta fish has the name 'fighting fish', as they will fight each other due to this aggressive nature.
Females on the other hand, are generally less aggressive than male bettas, however, this is highly dependant on personality as some females can be just as aggressive as males.