Mottled mojarra

Where they come from

Mottled mojarra (Ulaema lefroyi) is a coastal marine fish from the Western Atlantic. You run into mojarras around sandy flats, seagrass edges, and nearshore areas where there is a mix of sand, rubble, and little critters to sift out of the bottom.

That habitat explains most of their quirks in a tank: they want room, they want stable saltwater, and they spend a lot of time nosing around the substrate looking for food.

Setting up their tank

This is not a nano fish and it is not forgiving. Plan for a larger, mature marine setup with lots of open swimming space and a bottom they can work. Think more "lagoon/sand flat" than "packed reef wall."

• Tank size: bigger is better. I would not bother under 125 gallons, and 180+ makes life easier (for you and the fish).
• Substrate: fine sand. They like to pick and sift. Coarse gravel can scrape mouths and just frustrates them.
• Rockwork: keep it tidy and stable, with open areas up front. A few low rock islands beat a wall of rock.
• Flow: moderate. Enough to keep oxygen up and waste moving, but not a constant sandstorm.
• Filtration: heavy. Big skimmer, lots of biological capacity, and a plan for nitrate control. They are messy eaters.
• Lid: tight. Mojarras can spook and jump, especially the first few weeks.

For numbers, keep it in normal reef-ish seawater: stable salinity around 1.024-1.026, temp mid-70s F, and avoid big daily swings. They handle a range, but they do not like surprises.

What to feed them

They are bottom-oriented micro-predators and pickers. In the wild they eat worms, tiny crustaceans, and whatever they can vacuum out of the sand. In a tank, the trick is getting them eating confidently and keeping weight on without polluting your water.

• Start foods: live or fresh-frozen options get them going fastest. Live blackworms (if you can source safely), live enriched brine, and frozen mysis are good starters.
• Staples once settled: frozen mysis, chopped shrimp, chopped clam, finely chopped squid, and quality sinking carnivore pellets.
• Feeding style: small portions 2-3 times a day at first. They do better with frequent small meals than one big dump.
• Targeting: I like to use a turkey baster and put food right onto the sand in a couple spots so they can "hunt" it.

If they ignore pellets at first, do not panic. Mix a few pellets into a thawed frozen mix so they accidentally taste them. Once they learn pellets are food, life gets much easier.

How they behave and who they get along with

Mojarras are alert, fast, and a little skittish. They are not usually "aggressive" in the classic sense, but they are competitive at feeding time and they can bully slower fish just by outcompeting them.

• Temperament: generally peaceful, but will snatch food from shy fish and can stress them out.
• Best tankmates: other semi-active marine fish that can handle competition (bigger wrasses, tangs in appropriate tanks, larger hardy damsels, some rabbitfish).
• Avoid: tiny gobies/blennies you want to keep fat, slow pipefish/dragonets, and very timid fish that will never win a meal.
• Inverts: expect them to eat small shrimp and worms. Decorative tiny shrimp are a gamble. Snails and larger cleaner shrimp can be hit-or-miss depending on the individual.

They can be kept singly. Groups are possible in a very large system, but you need space and you need to watch for one fish getting pushed off food. If you try multiple, add them at the same time and feed heavy at first.

Breeding tips

Breeding this species in home aquariums is not really a "project" most hobbyists pull off. Mojarras are typically broadcast spawners with pelagic eggs and larvae that need specialized rearing setups and live plankton at the right sizes.

Common problems to watch for

Most issues with mottled mojarras trace back to three things: stress from capture/shipping, not eating enough early on, and water quality slipping because they are hearty eaters.

• Refusing food: very common the first week. Dim lights, offer live/frozen, and give them quiet time. Too much foot traffic and sudden movement can keep them spooked.
• Thin fish that never fills out: usually not enough feeding frequency or they are losing food to faster tankmates. Separate or target-feed.
• Parasites (marine ich/velvet/flukes): wild-caught coastal fish can come in hot. Quarantine is your friend here.
• Mouth/nose abrasions: happens if they slam the glass when startled or if the substrate is too rough. Provide sand and keep reflections down.
• Jumping: spook response. Tight lid and cover gaps around plumbing and cords.
• Nitrate creep: they are messy. Skim wet, siphon detritus, and do not let leftover food sit in the sand bed.

One last practical thing: keep a calm routine. Same lights, same feeding spots, same approach to the tank. Once they learn you are the food person and not the predator, they settle in and get a lot easier to manage.