Spine-tailed round ray

Where they come from

Spine-tailed round rays are small coastal stingrays from the eastern Pacific, showing up along Central and northern South America on soft sand and muddy bottoms. You find them in shallow bays, estuaries, and near river mouths where the bottom is silty and full of crustaceans. They spend a lot of time buried with just eyes and spiracles showing.

Setting up their tank

Footprint matters more than gallons. A single adult is happiest in something like an 8 x 3 ft footprint (around 350-450 gallons). I kept mine in a 7 x 3 ft lagoon-style system and always wished for another foot of length.

• Substrate: 2-3 inches of fine aragonite or sugar-grade sand. No crushed coral, no sharp rubble.
• Aquascape: Keep rock to the back or on a PVC/egg-crate base. Leave a big open runway of sand for cruising and burying.
• Flow: Moderate and broad. Use guarded powerheads or low-mounted returns aimed to keep the surface rippling. Avoid jet streams at sand level.
• Filtration: Big skimmer, big sump, and lots of oxygen. Rays are messy eaters. Plan for 6-10x system turnover through the sump.
• Guards and covers: Heater in the sump, guards on pump intakes, mesh on overflow teeth. Rays wedge into weird places.
• Lighting: Dim to moderate. They get active at dusk; bright reef lighting is fine if you give shaded zones.
• Lid: Tight mesh or acrylic lid. They do not usually jump, but they can surge hard during startles.

Target parameters I have used: 1.023-1.025 sg, pH 8.1-8.3, temp 74-78 F (23-26 C), ammonia/nitrite 0, nitrate under 20 ppm. Keep oxygen high and temp stable. A chiller or solid climate control is worth it in warm rooms.

What to feed them

Mine switched over to tongs in about a week. The trick was to bury a small piece in the sand, let it sniff it out, then present the next bite right at the snout with long tongs. Once they connect you with food, feeding gets easy.

• Staples: fresh/frozen shrimp, squid strips, scallop, and marine fish like silversides or smelt (in moderation).
• For teeth wear and enrichment: clam or mussel on the half shell, crab legs split so they can work on them.
• Supplements: rotate foods and soak a couple meals a week in a vitamin mix (e.g., Selcon) to avoid B1 issues from thiaminase-heavy items.
• Schedule: juveniles - small meals daily; adults - every other day. Watch body shape more than the calendar.

Good body condition looks like a smooth, slightly rounded disc with no hip bones showing and a gentle bulge behind the head after meals. If the tail base starts to look pinched, increase frequency; if they look puffy and lazy, cut portions.

How they behave and who they get along with

They are calm, sand-hugging hunters. Lots of burying, short cruises, then periods of stillness. Most activity is at dawn and dusk. Mine ignored midwater fish and focused on the sand for snacks.

• Good companions: bigger, peaceful swimmers that do not pick at fins, like tangs, rabbitfish that mind their own business, larger wrasses that stay midwater. Keep the vibe chill.
• Risky: angels and butterflies that nip, aggressive wrasses, large groupers that might try a bite, boisterous triggers and puffers (nippers).
• Inverts: crabs, shrimp, small snails are food. Urchins and big conchs usually get left alone, but plan on manual sand maintenance instead of a cleanup crew.
• Other rays: only in very large, wide systems. Males may badger smaller individuals.

Breeding tips

They are livebearers. In home aquariums, breeding is rare and usually accidental in very large lagoons. If you try, you will need a big group to pair off naturally and lots of sand space. Males can pester females, so sight breaks and multiple hides help. Gestation is several months and litters are small. Newborns take tiny pieces of shrimp and chopped clam within a day or two.

Common problems to watch for

• Substrate abrasions: red sores on the disc or tail tip usually come from rough sand or rubble. Switch to finer sand and keep the bed clean.
• Low oxygen stress: heavy breathing, hanging at the surface, or parking under a return. Add surface agitation and check temp.
• Internal parasites or flukes: poor appetite and weight loss. Praziquantel is one of the few treatments rays tolerate well; skip copper and formalin.
• Copper sensitivity: copper meds can kill them. Treat inverts/fish in a separate system if you must use copper.
• Powerhead and overflow injuries: they wedge into intakes and slots. Guard everything that sucks.
• Dental plate overgrowth: if you feed only soft foods, they may struggle to crush prey. Offer clam on the half shell weekly.
• Nutritional gaps: limp posture and poor recovery after meals can be diet-related. Rotate foods and add vitamin soaks.
• Obesity: they beg like puppies. Keep portions reasonable and watch that tail base does not get fat rolls.