We received, as a gift, a betta fish in a fishbowl that had gravel at the bottom. Does the gravel have any practical purpose? Is it just there to look pretty?
It’s aesthetic. If you don’t have gravel, fish poop will drop to the bare glass and sit there, like a turd in a punchbowl. With some gravel, the detritus will be camouflaged.
Gravel plays host to bacterial colonies that help to process ammonia into nitrites and then into nitrates. Ammonia and nitrites are both harmful to fish, so a lack of those bacterial colonies will mean high fish death rates. This is one reason why tanks are usually run empty (or with only a few hardy fish) for a few weeks before introducing the final inhabitants.
There are other places the bacteria could survive, I suppose, but the gravel also looks nice and hides waste that would float to the bottom.
The bacteria in question grow on surfaces. Gravel greatly increases the surface area available in a tank*, and helps support a relatively large population of these critically important little guys. As dracoi stated, they are the key to the nitrogen cycle.
*if you want an explanation of how that works I can dig one up
Thanks, all. I guess I’ll leave it in, then.
In larger aquariums, the gravel can facilitate a biological balance (bacteria that eats the waste, etc.). A betta bowl is usually pretty small and you should change out the water frequently, so it won’t build up a bacterial balance, anyway. So I would say the gravel is just for looks.
It’s a greater concern if there’s something on top of the fish bowl, rather than what’s at the bottom. For a while (and maybe still, in some places that haven’t gotten the memo), stores were selling bettas in non-aerated vases with floating plants on top. The advertising shtick is that the fish can live on the roots of the plant, creating a self-sustaining mini-ecology, but in reality bettas in this environment will slowly die of suffocation and/or poisoning as the roots die and/or starve to death–you see, they’re carnivorous and MUCH prefer mosquito larvae to plant matter. And their water has to be changed pretty often, because of the nitrogen issues explained above. Lots of casual fish owners don’t know this, and many innocent bettas have been killed in the pursuit of home decor. (not that it’s a huge deal, they’re just fish, but still–why kill it if it can be avoided?)
So, I’m glad you got your fishie in a bowl instead of in a vase. And if you ever see anyone give or receive a betta vase, sneak in there and put it in a proper bowl or tank instead!
I’d leave it in; anything you can do to increase the area for the beneficial bacteria to grow is going to help you out in a small unfiltered container. At least that may help a little to decrease the ammonia build-up, although frequent water changes are going to be most important.