Sir Stigmatogobius sadanundio
The Knight Goby goes by the scientific name, Stigmatogobius sadanundio. The Stigmatogobius part comes from a blend of Latin and Greek. Stigma loosely means “marked” in Greek, and gobius translates to “gudgeon” from Latin. The sadanundio part is the Bengali name for this fish, and this was the native name for it when and where it was first found and cataloged for science. The Knight part we have wondered about publicly before. Most people don't call it “sir,” so it almost surely has not been Knighted, regardless of its history.
These curious little fish can be found swimming along in streams all over southeast Asia, India, Pakistan, Sri Lanka, Myanmar, Thailand, Cambodia, Singapore, Sumatra and maybe more. They are often found in brackish water, but usually more in the freshwater reaches of the estuaries. They can be kept in slightly brackish water, up to about 1.005 specific gravity, but we recommend keeping them in hard, basic water, the pH should be somewhere in the 6.- to 7.0 range and the hardness between 10 and 20 GH. Keeping them in either fresh or brackish water is a good choice, just avoid overly soft or acidic conditions. They do well when kept in tanks that are between 70- and 78-degrees Fahrenheit.
The Knight Goby is a really pretty fish. They range from a cream color to a pale golden (females usually more on the yellowy side), with sporadic little black dots speckled along their sides. They have beautiful dorsal fins that feature the most amazing, little iridescent spot, the color of a Bahamian ocean on a brilliant summer day. They only get about three inches long and so one could be kept in a 20-gallon tank. You could keep more together, but you'll need enough space for them all to establish a little territory unless they are a mated pair. The love cover and especially caves, so offer them plenty of rocks to hide in and swim around. Knights are naturally nocturnal, but will be plenty active during the day as long as the aquarium is dimly lit. They can be kept in planted aquariums, given the plants are appropriate for their preferred water chemistry. The plants should also be of the variety that either float (which helps keep the lighting subdued) or that get attached to décor to prevent the Gobies from digging them up as they rummage about in the substrate. We do suggest having some soft sand in their displays.
One of the nicest things about keeping Knight Gobies is how easy they are to feed. They'll accept a wide variety of food and will even graze on some algae. Here we give them a mix of meaty foods from Gamma including Brine, Brine Plus Spirulina, Brine Plus Garlic, as well as Bloodworms, Tubifex and Mosquito Larvae, and unsurprisingly, they'll relish any opportunity to have these foods live as well. They are known to do a bit of grazing on any algae you may have in the aquarium and so we also love to offer them the Nutramar Freshwater Algae and Color Plus shots which allows them some grazing opportunity and is a great formula for them. Because they are active in low light periods, you may need to feed them at lights out and lights on initially, but they'll become accustomed to daylight feedings over time. Feeding once a day is fine and twice a day would be fine too, just reduce the amount of food per feeding.
Stigmatogobius sadanundio is a beautiful and unusual addition to the community aquarium as long as you make good choices about tankmates. These fish are going to stay near the bottom of the aquarium and might be aggressive with other fish that inhabit this same range, especially if the aquarium is too small, or those fish look like / act like Knight Gobies. They are predators and will not hesitate to make a meal of anything small enough for them to eat. Other than that, they are likely going to ignore everything else in the tank. Choose fish that like similar water chemistry, like Rainbowfish, Mollies, Archerfish etc. If you're going for a brackish display, Monos, or the very strange Anableps could work.
As we mentioned earlier, you can keep more than one Knight Goby if you have enough space. The benefit here is that if you end up with a male and a female, there is a chance they could breed in your aquarium. There are documented reports of successful reproduction in hobbyist's aquariums, but they are rarely commercially aquacultured. These fish are cave spawners and have an interesting courtship ritual. The parents will pick a cave, then after a bit of a dance, female will lay her eggs in it and then the male will defend the eggs until they hatch. At this point, the fry are unprotected and likely to be eaten by anything and everything that can eat them, including their parents, so remove them from the display if rearing the fry is your goal. Some hobbyists have reported that large water changes with fresh water can trigger spawning events.
The Knight Goby is a delightful fish to have, watch and care for. They are pretty and interesting with behaviors that are distinct from many of the fish that are commonly available to the freshwater aquarist. They might be a tad shy when first added to the tank, but they'll become more gregarious as they settle in and more active during daylight as they get used to getting most of their food then. If Sir Stigmatogobius sadanundio sounds like something you're interested in having in your tank, or if you are the kind of hobbyist that is looking for a new aquaculture challenge, think about making a Knight Goby the defender of your aquarium sand bed! realm! Ask your LFS to get you one from Aquatropic today!