Zamboanga priapiumfish

Where they come from

Neostethus zamboangae is one of those tiny, blink-and-you-miss-it coastal fishes from the Philippines (Zamboanga area). Think mangrove edges, tidal creeks, and calm, shallow water that swings between fresh and salty depending on rain and tides. That "swing" is basically the whole story with this species.

Setting up their tank

These are expert-level mostly because they are small, delicate, and not forgiving about water quality or rough handling. The good news is you do not need a huge tank. You do need a mature one.

• Tank size: 10-20 gallons works, but bigger makes stability easier.
• Tank age: set up and running 2-3+ months before you add them. "New brackish" is where tiny fish go to disappear.
• Filter: sponge filter or a gentle HOB with a prefilter sponge. They hate being blasted around.
• Flow: low. If you see them constantly fighting current, dial it back.
• Substrate: sand or very fine gravel. They spend a lot of time low in the water and around cover.
• Cover: clumps of fine-leaved plants (even if you use brackish-tolerant options like java fern on wood), algae-covered rock, leaf litter, or artificial grass-like spawning mops.
• Lighting: not crazy bright. They color up and feed better with some shade.

For salinity, I have had the best luck keeping them in low-end brackish and not messing with it all the time. Something like specific gravity 1.003-1.008 is a good practical range for many Neostethus setups, but match what your group was kept in if you can. Sudden swings hit these little guys hard.

Aim for warm, stable temps (mid-70s to low-80s F). Keep ammonia and nitrite at zero, and keep nitrate low. With small fish, you notice problems faster because they do not have much "buffer" in their bodies.

What to feed them

Feeding is where most people lose them. They are tiny-mouthed micro-predators. Many will ignore flakes and pellets, especially at first. Live and frozen foods are your friend.

• Best staples: baby brine shrimp (BBS), newly hatched or small live foods, copepods, and other "speck-sized" critters.
• Frozen options: cyclops and finely sieved daphnia can work if the pieces are small enough.
• Occasional treats: grindal worms chopped small, mosquito larvae only if they can handle the size (often too big for smaller individuals).
• Prepared foods: some can be trained onto powdered fry foods or crushed micro pellets, but do not count on it early on.

Feed small amounts 2-3 times a day if you can. They do better with frequent tiny meals than one big dump. Watch their bellies after feeding. You will get a feel for who is eating and who is getting outcompeted.

How they behave and who they get along with

They are peaceful and kind of shy, but they are not dumb. In a calm tank, you will see little displays and quick darts as they pick at micro-food. Keep them in a group if possible. Singles tend to hide and fade.

Tankmates are the tricky part. Anything even slightly boisterous will outcompete them at feeding time or just stress them into not eating.

• Best kept: species-only, or with other tiny, gentle brackish microfish.
• Avoid: scats, monos, most puffers, larger gobies, archerfish - basically anything that makes splashing/charging normal.
• Also avoid: fin-nippy stuff and "busy" livebearers. Even if they are not predators, they will vacuum up the food before priapiumfish get a chance.

Breeding tips

If you get them settled and well-fed, breeding is possible, but it is not like tossing guppies together. Priapiumfish have weird, fascinating reproductive anatomy (the "priapium"), and they are not the easiest to raise past the first tiny stages.

• Keep a bigger group: you are more likely to end up with both sexes and natural pairings.
• Condition with live foods: BBS and copepods make a difference.
• Give them structure: dense plants, mops, and calm corners. They like having places to retreat and display.
• Raise fry foods ahead of time: if fry show up, you need microscopic food ready, not "tomorrow."

Common problems to watch for

Most issues trace back to three things: unstable salinity, not enough tiny food, and stress from flow/tankmates.

• Not eating: usually food size is wrong, or the tank is too "sterile." Start BBS and add pods if you can.
• Sudden losses after water changes: salinity or temperature mismatch. Mix water fully, match temp, and match specific gravity before it goes in.
• Getting sucked into filters: intake sponges are non-negotiable with fish this small.
• Wasting away slowly: they may be losing the feeding competition. Try target-feeding with a pipette in a quiet corner.
• Ich/velvet-type outbreaks: stress and swings bring it on fast in brackish. Quarantine new arrivals and keep changes gentle.

If you treat them like a "micro predator" that needs calm water, tiny live foods, and steady brackish conditions, they are incredibly rewarding. Once they settle, you will start noticing all the little interactions that make them special.