Bubble nest

Bubble nests, also called foam nests, are created by some fish and frog species as floating masses of bubbles blown with an oral secretion, saliva bubbles, and occasionally aquatic plants. Fish that build and guard bubble nests are known as aphrophils.^[1] Aphrophils include gouramis (including Betta species) and the synbranchid eel Monopterus alba in Asia, Microctenopoma (Anabantidae), Polycentropsis (Nandidae), and Hepsetus odoe (the only member of Hepsetidae) in Africa, and callichthyines and the electric eel in South America.^[1] Most, if not all, fish that construct floating bubble nests live in tropical, oxygen-depleted standing waters.^[1] Osphronemidae, containing the bettas and gouramis, are the most commonly recognized family of bubble nest makers, though some members of that family mouthbrood instead. The nests are constructed as a place for fertilized eggs to be deposited while incubating and guarded by one or both parents (usually solely the male) until the fry hatch.

Bubble nests can also be found in the habitats of domesticated male betta fish. Nests found in these types of habitats indicate a healthy and happy fish.^[2]