Fighting fish are just big softies on the inside.
Why build a nest if you’re a fish? A bird’s nest can be up in a tree to keep away from predators, but a fish nest is, well, in the water. Siamese fighting fish (Betta splendans) are one of several aquarium fish that are bubble nest-builders. The male builds the nest and cares for the eggs after laying. Indeed, the male drives the female away from the nest.
One of the problems with putting all your little developing embryos or babies in a confined space like a nest is that if an infection hits, it might hit all of them. Betta nests without males are often hit by water molds (the same obscure group of organisms that also cause crayfish plague). Lots of other animals have some element of their nest that act as antimicrobials, and Brown and Clotfelter hypothesized this might also be true for the fighting fish.
Reasonable idea, but wrong.
They tested bubble nest material against two bacteria and a water mold. There was no evidence any of the bacteria were held back or inhibited by the nest material compared to a control.
Surprisingly, the presence of the nest material, made things worse With the water mold! More eggs were infected faster in the presence of bubble nest material than in plain water. Nests seem to be a horrible idea!
But wait! Brown and Clotfelter suggest that nests have an important function. Siamese fighting fish are popular in aquariums precisely because they are used to living in very low quality water, with little oxygen. The nests may be necessary to keep enough oxygen to the eggs for them to develop. And, because so few other animals can live in the same waters as Siamese fighting fish, the risk of predation may not be very high.
It might explains why you have parental care by these fish: this may be the one thing keeping those eggs viable and parasite free.
It’s nice to see that there are still interesting research projects that can be done even with these common aquarium pets.
Brown AV, Clotfelter ED. 2012. Fighting fish (Betta splendens) bubble nests do not inhibit microbial growth Journal of Experimental Zoology A: in press. DOI: 10.1002/jez.1740