Cobalt blue goby

1) Where they come from

Cobalt blue gobies (Stiphodon semoni) come from clear, fast-flowing island streams (Indonesia/Philippines region). Think shallow runs over rocks, tons of oxygen, and a buffet of algae and biofilm on every surface. That “river” vibe is basically the whole trick with this fish.

2) Setting up their tank

If you set the tank up like a calm community tank, they usually fade into the background and slowly get skinny. Give them current, oxygen, and lots of rockwork they can graze on, and they turn into little busy workers that show off all day.

• Tank size: 10–20 gallons works for a small group, bigger is easier because you get more grazing area
• Flow: strong directional flow (powerhead or a canister return) so there’s a “river lane”
• Oxygen: surface agitation + a filter that moves real water; they love it
• Hardscape: rounded river stones, smooth rocks, and some wood—more surface = more food
• Substrate: sand or fine gravel is fine, but rocks are where they spend their time
• Plants: optional; use tougher stuff (Anubias, Java fern) attached to rocks/wood so it isn’t blasted around

They’re jump-capable when startled, especially during first-week jitters. A lid (or at least covering the big gaps) saves heartbreak.

3) What to feed them

Most cobalt blue gobies are micro-grazers first and “prepared-food eaters” second. Some learn fast, some act like pellets are imaginary. Your job is to give them a steady trickle of small foods and keep natural grazing available.

• Staples they usually take: frozen baby brine shrimp, cyclops, daphnia
• Great add-ons: Repashy (soilent green / community), smeared thin on a rock so they can rasp at it
• If they accept it: small sinking pellets, crushed flake (but don’t rely on it at first)
• Natural buffet: algae/biofilm on stones, botanicals, and tank walls (within reason)

Watch their bellies. A healthy fish has a gently rounded belly after feeding and doesn’t look pinched behind the head. The “silent failure” with Stiphodon is slow starvation in a tank where everyone else looks fine.

4) Behavior and tankmates

They’re peaceful little river gobies that spend their day perched on rocks, scooting, grazing, and occasionally doing quick displays. Males can bicker and posture, but it’s usually more drama than damage as long as there’s room and multiple perches.

• Good tankmates: small peaceful fish that like similar water (small rasboras, peaceful danios), otocinclus, Amano shrimp
• Tankmates I avoid: fin-nippers, boisterous feeders, big curious cichlids, anything that hogs the bottom and stresses them
• Group size: 1 works, but 3–6 is more fun if you have enough rock territory

5) Breeding tips (the reality check)

You might see courting and spawning behavior in freshwater—males intensify in color and guard a little spot under a rock. The catch is the babies are amphidromous: the eggs hatch, larvae drift, and they need brackish/marine conditions to make it past the larval stage.

• What you can do in freshwater: provide flat stones/caves, stable water, and a good diet so adults condition up
• If you want to attempt raising fry: you’re looking at a separate larval system, live plankton foods, and managing salinity changes over time
• Most hobbyists: enjoy them as display fish and don’t stress about breeding

6) Common problems to watch for

These gobies don’t usually explode with obvious disease. The usual issues are slow and sneaky: weight loss, stress from low flow/low oxygen, or getting bullied off food.

• Slow starvation: sunken belly, reduced activity, staying in one corner—fix with mature tank biofilm + targeted small foods
• Low oxygen/low flow: hanging near the surface or filter output—add surface agitation and stronger circulation
• New tank syndrome: they do poorly in immature setups with no grazing and unstable parameters
• Parasites from wild-caught stock: stringy poop, weight loss despite eating—quarantine helps a lot
• Jumping: especially after introduction or during scuffles—use a lid