Redrump blenny

Where they come from

Redrump blennies (Xenomedea rhodopyga) are little rock-huggers from the eastern Pacific side of things. You see them associated with shallow, rocky reef and rubble zones where there are tons of cracks, empty shells, and little burrows to duck into. That background matters because in the tank they want the same deal: hard structure, real hiding spots, and a steady supply of surface growth to pick at.

Setting up their tank

I would not keep this species in anything smaller than a mature 20-30 gallon, and bigger is easier. They are tiny, but they act like they own a few square feet of reef, and they get braver (and eat better) when they have a home base they can defend.

Build the aquascape with lots of tight holes and short tunnels. Think "blenny-sized". A few small caves, a chunk of branching rock, and a rubble corner goes a long way. If you give them one obvious prime hole, they will usually claim it and settle down fast.

• Mature tank: I like 6+ months old with visible microfauna and some film algae
• Rockwork with crevices: multiple bolt-holes so they can retreat without getting trapped
• Moderate flow: enough to keep food moving, not a sandblaster aimed at their favorite perch
• Stable salinity and temp: keep swings small, they do not love yo-yo parameters
• Lid/cover: blennies can launch when spooked, especially new arrivals

What to feed them

Getting them eating is the whole game. The ones I have had did best with frequent small feedings and a mix of meaty foods plus some grazing opportunities. If you only offer flakes once a day, they can look fine for a while and then slowly waste away.

Start with what they can sniff out easily: frozen foods with some scent. Once they recognize your feeding routine, you can broaden the menu.

• Frozen: mysis (small), chopped brine shrimp, finely chopped clam or mussel, roe if you can get it
• Live (great for new fish): live brine, copepods, blackworms if you have access and can rinse well
• Prepared: small sinking pellets (marine) once they accept non-moving food
• Grazing: they will pick at film algae and micro-stuff on rock, but do not count on that as the main diet

How they behave and who they get along with

They are classic blenny attitude in a small package: perch, watch, dart, and defend a spot. Most of the time they are entertaining and bold, but they can be surprisingly spicy with other bottom-dwellers that want the same real estate.

In my experience, they do best with calm fish that stay in the water column and do not sit on the rockwork all day. If you pack the tank with other perchers, the redrump spends too much time hiding and not enough time eating.

• Good tankmates: small peaceful wrasses, chromis/anthias types, dartfish, small cardinalfish, mellow gobies that stick to sand more than rock
• Use caution: other blennies (often turns into a turf war), hawkfish (may bully), dottybacks (too pushy), aggressive damsels
• Risky: big crabs, large shrimp that steal food, any fish that relentlessly picks at perched fish

Breeding tips

Breeding behavior is interesting if you like watching fish be fish. They are cave/spawn-site oriented, and the male will usually claim a hole and try to keep a female interested. You may see the male cleaning a spot, doing short little display dashes, and guarding the entrance more intensely.

Raising the babies is the hard part. The larvae are tiny and pelagic, so you are in rotifer-and-greenwater territory, and you need a separate larval setup with gentle flow. If you just want to observe spawning and guarding, that is doable in a display. If you want to rear them, plan it like a serious project.

• Give them a proper nest: narrow caves, empty shells, or a small length of PVC tucked into rock
• Feed heavy but keep water clean: conditioning adults usually means more food and more export
• If you see eggs: expect guarding and increased aggression around the nest
• For rearing: separate larval tank, rotifers ready, stable salinity, and patience

Common problems to watch for

Most issues I have seen with redrump blennies come down to food and stress. They can arrive skinny, get outcompeted, or be harassed off the rockwork until they basically stop showing themselves.

• Slow starvation: looks "fine" at first, then the body narrows behind the head and the belly stays pinched
• Feeding competition: faster fish eat everything before the blenny commits
• Territory stress: constant chasing from another percher leads to hiding and weight loss
• Jumping: especially in the first week or after a scare
• Parasites on new arrivals: flashing, excess mucus, rapid breathing - quarantine helps a lot