Insolitus sand eel

Where they come from

Yirrkala insolitus is one of those oddball sand-eel style fishes that pops up in the Indo-West Pacific region. Think shallow coastal areas where the bottom is a mix of sand and rubble, and the fish survives by staying out of sight most of the time. If you are used to reef fish that pose for you all day, this one is the opposite.

Setting up their tank

The whole game with Insolitus sand eels is substrate. Give them the wrong sand and you will have a stressed fish that refuses food, constantly tries to wedge under rock, or scrapes itself up.

• Tank size: I would not bother under 30 gallons, and 50+ is nicer just for stability. They do not need tons of open swimming space, but they do need consistent water and room to establish a hiding routine.
• Substrate: fine sand, deep enough that it can fully disappear (I like 3-4 inches minimum). Avoid sharp crushed coral.
• Rockwork: keep it stable and sitting on the glass or on supports, not perched on sand that can shift when the fish digs.
• Flow: moderate. Too much direct blast and they will struggle to settle. Dead spots are fine as long as you keep nutrients in check.
• Cover: tight lid. If they get spooked at night, they can launch.

Lighting is whatever fits your system. Bright reef lights will not kill them, but it can make them extra secretive. I have had better "sightings" in tanks with shaded areas and a calmer vibe.

What to feed them

Plan on a finicky start. A lot of these come in skinny, and they do not always recognize pellets or flakes as food. Once they are eating, they usually keep eating, but getting there can take patience.

• Best starters: live foods (blackworms if you can do them marine safely, live ghost shrimp acclimated, small live mollies converted to salt can work in a pinch).
• Reliable frozen: mysis, enriched brine, chopped krill, chopped clam, and any small meaty mix meant for carnivores.
• How to offer: use feeding tongs or a turkey baster and squirt food right at the burrow entrance. They often strike from the sand like a little trapdoor.
• Schedule: small portions daily at first. Once weight is on, you can do every other day, but watch body condition.

A feeding trick that helped me: feed the tank normally, then come back 10 minutes later and target-feed the sand eel after the busy fish are distracted. They hate chaotic food storms.

How they behave and who they get along with

Most of the time they are invisible. Then you will notice eyes poking out of sand, a quick dart, and they are gone again. They are not a "centerpiece" fish unless you are the kind of hobbyist who enjoys hunting for subtle movement.

• Temperament: generally peaceful toward similar-sized fish, but anything small enough to fit in the mouth can get eaten.
• Tankmates I avoid: aggressive feeders (large wrasses, big dottybacks), fish that pester the sand (some gobies that constantly dig), and anything that will bite at a head sticking out of sand.
• Tankmates that tend to work: calmer community reef fish that do not live on the bottom (chromis, cardinals, smaller tangs in larger tanks, many peaceful anthias if you feed enough).
• Inverts: shrimp and tiny crabs can be a gamble. If it moves like food and fits, it might become food.

If you keep more than one, do it only in a big tank with lots of sand real estate and multiple hiding zones. Even then, I would not call it predictable. Most folks keep them singly for a reason.

Breeding tips

Realistically, breeding Yirrkala insolitus in home aquariums is in the "nice if it happens" category. They are secretive, likely spawn in ways we rarely witness, and raising larvae (if pelagic) is its own full-time project.

• If you want to try: keep a well-fed pair, run a calm, stable system, and give them lots of undisturbed sand and low-traffic zones.
• Look for clues: sudden hiding changes, a noticeably plumper fish, or odd nighttime activity.
• If you ever see eggs/larvae: be ready with rotifers, copepods, and a dedicated rearing setup. Do not expect the display tank to raise them for you.

Common problems to watch for

These are expert-level mostly because they are unforgiving about acclimation, feeding, and stress. A healthy one is fairly hardy, but getting it established is the hard part.

• Refusing food: usually stress, too much competition, or the fish not recognizing prepared food yet. Try live, target-feed, and reduce activity around the tank for a few days.
• Scrapes and mouth damage: commonly from rough substrate or frantic burrowing against sharp rubble. Fine sand fixes a lot of this.
• Rockwork shifts/collapses: caused by digging under rocks. Build rock structures to be dig-proof from day one.
• Jumping: almost always a spook response. Tight lid and no gaps around plumbing.
• Parasites after import: keep an eye out for rapid breathing, flashing, and excess mucus. Quarantine is hard with a sand burrower, but skipping it can bite you later.

The best "health check" with these is body shape. You want a fish that looks filled out behind the head and along the body, not pinched or stringy. If it is losing weight, change something fast: quieter feeding, more frequent small meals, and less competition usually turns the corner.