One of the most unique aspects of having a male betta fish is their bubble nest. Male betta fish blow a special kind of sticky bubble that can be clumped together on the surface of the water to create what is called a “bubble nest”. In the wild, the male betta will bring a female to the nest to mate (he hugs the eggs out of her, then gathers them up and sticks them to the bubbles). The male betta will then guard the eggs, and the baby fish (called “fry”) after they hatch.
A nesting betta is considered a happy betta, and also a betta that is ready to mate. Although these two aspects are generally a part of any nest, you can sometimes tell the difference between whether your fish is building a nest because they’re happy or because they’re ready to mate. Finley likes to always have a nest in his tank, but he’s a very happy fish most of the time. He will clearly go work on the nest when he’s extra happy though – after he gets a water change, while he’s watching cartoons (yes, he actually stops watching the cartoons to go over and gleefully blow more bubbles into his nest, and then go back to watching cartoons, then back to blowing bubbles, and so on), etc.
When he’s nesting specifically to mate, he works almost non-stop for several days sometimes building as big of a nest as he can. Sometimes there are so many bubbles that they start creating layers. During that time, he’s more temperamental than usual – he flares at just about everything, like his food, plants, even me. After the nest is built, I usually find glob of white/clear stringy goo. The general consensus on the internet seems to be that the goo is a mucus from his labyrinth organ – I’m guessing that he produces so much of it to make all the bubbles, that he ends up having some left over and it just ends up sticking to something in the tank. The other theory is that it is sperm, which is called “milt” in fish terms, though it is thought to be microscopic (and not a visible goo).
Sometimes, he makes more than one nest. As you can see in the picture to the left, one time he even made four different nests! That was the most he has ever made for individual nests. The bubble nests can last anywhere from several days to several weeks if they are undisturbed.
If you clean the tank carefully with a gravel vac, some of the nest can survive – they’re incredible sturdy. I’ve seen them stick to the tank wall as the water drained out, then gather back on the surface as the water was added back in again!
There are a couple different ways that a nest can begin. Usually he will blow bubbles in a clump and just keep adding to it very intentionally. Sometimes he gets creative though and will blow bubbles all over the place and then gather them up and stick them together later – I call the start of that kind of nest a “bubble galaxy”. Here is an example of a bubble galaxy that 12 hours later was a thick nest – it’s 5 bubbles high at it’s tallest point.
He tends to build the nests in the same spot over and over, but sometimes he does try out new locations. Here is a video of what happened when he tried to build a bubble nest near the filter:
To see more of Finley’s bubble nests, check out #ArchitectFish on Twitter.