Bubblenests, also spelled bubble nests or bubble-nests, created by some fish species, are floating masses of bubbles blown with an oral secretion, saliva bubbles, and occasionally aquatic plants, or an area for egg deposit attached at the bottom.
Species which build Bubblenests
Gouramis (including Betta species) and some sunfish, catfish and cichlids create bubblenests. Anabantidae are the most commonly recognized family of bubblenest makers. The nests are constructed as a place for fertilized eggs to be deposited while incubating and guarded by the male until the fry hatch. They can often be seen above a content male betta.
Construction of Bubblenests
The nests are always built by the male and their size, position and shape depends on the species. The nest is most often made at the water surface, sometimes among floating plants, whether natural or artificial. Occasionally, every object floating will have bubbles on it.
Bubble nests created by male betta/Siamese Fighting Fish (Betta splendens) are made from air bubbles coated with saliva to increase durability. This makes a louder noise than regular breathing and is often frantic behavior.
Bubblenests and Breeding
After spawning, the eggs float up into the bubble nest, or are carried there held in the mouth by the male, as if he is eating them. The male lodges them in the nest to protect them, and then protects the brood by chasing away the female and any other intruders, concentrating on the eggs in the nest, retrieving any eggs or fry that fall from the nest and keeping the nest in repair. The father will guard the eggs constantly until the fry hatch in 24-48 hours and be suspended from the nest. For the next few weeks, they will stay nearby being tended by the father.
Triggers of Bubblenest Construction
Bubble nests are built even when not in presence of female or fry (though often a female swimming past will trigger the frantic construction of the nest). Males will build bubble nests of various sizes and thicknesses, depending on the male's territory and personality. Some males build constantly, some occasionally, some when introduced to a female and some do not even begin until after spawning. Some nests will be large, some small, some thick.
Various things have been shown to stimulate bubble nest construction, such as quick temperature changes, barometric changes, materials in the tank and presences of other males or females.
-  - A video of two Siamese Fighting Fish spawning. The male can be seen carrying eggs up to the bubblenest.