Neil Monks gives his advice to a reader who would like to set up a brackish biotope for bumblebee gobies.
Q) I’d like to set up a brackish biotope for bumblebee gobies. How many could I keep in a 60 l set-up and what food should I offer them? What’s the best way to furnish the tank to best resemble their natural environment?
PAULA SPENCER, VIA EMAIL
A) NEALE MONKS RESPONDS: The idea that bumblebee gobies are brackish water fish is only partly true. Identifying these gobies is notoriously difficult, and as one goby taxonomist has put it to me, the only thing you can be sure of with bumblebee gobies is that you won’t have the species usually described in aquarium books! This species, usually called Brachygobius xanthozona (though more correctly described as Hypogymnogobius xanthozona), is extremely rare and hardly exists even in museum collections, let along tropical fish tanks.
In fact the most common species in the UK trade is probably Brachygobius doriae, although other species do get shipped. B. doriae is found across Indonesia and Malaysia, where it inhabits coastal creeks and streams, sometimes in brackish water and sometimes in fresh. In freshwater habitats it can be found in even quite soft and even acidic water conditions. With that said, aquarists generally find they do best in either neutral to slightly hard freshwater, or else slightly brackish water with a specific gravity around 1.002-1.003.
Bumblebee gobies can be difficult to feed and generally prefer live foods such as brine shrimp, often needing to be weaned onto frozen alternatives like bloodworm. While this doesn’t take long, even when taking frozen foods they’re slow feeders, and therefore compete badly with more active tankmates. The best tank for Brachygobius is one where they’re kept alone, but if you must choose tankmates, select species that won’t compete for food. Wrestling halfbeaks (Dermogenys spp.) are an obvious choice. Since halfbeaks find it difficult to take food from the substrate, there should be little competition between the two species. Coming from the same part of the world and inhabiting similar environments, their water chemistry requirements are also a match, both doing well in either moderately hard freshwater or low-end brackish conditions. It’s good to have the option of adding salt even if you set the tank up as a freshwater system to begin with. That way, if you find your fish looking a little off-colour, you can add some brackish water to the system and they should perk right up. Slightly brackish conditions will also do a good job of inhibiting many parasites (including whitespot) while also allowing brine shrimp to stay alive long enough for your fish to eat them.
So far as the environment goes, these are fish that inhabit shallow streams in rainforests and elsewhere. Submerse vegetation is uncommon, and the water is often silty or stained with peat. Being territorial, the males need definite hiding places which they’ll use either for spawning or to escape from other males. Bogwood roots, coconut shell caves and leaf litter should all work fine, with a silica sand substrate (or a dark volcanic sand if you prefer). There are all sorts of Southeast Asian plants that would be appropriate, but Cryptocoryne ciliata is not only native to this part of the world, but would be able to handle slightly saline conditions. It does get a bit big though, so if you wanted smaller plants rather than one or two big specimens, Cryptocoryne wendtii handles slightly brackish water with aplomb.