Saw-spined round ray

Where they come from

Saw-spined round rays (Urotrygon serrula) are western Atlantic stingrays from warm coastal waters. You are looking at a bottom-dweller that spends a lot of time half-buried in sand in bays and nearshore areas. That natural lifestyle drives basically everything about how you keep them in a tank.

Setting up their tank

Think footprint first, not gallons. Round rays need open floor space and a sand bed they can bury into, and they hate sharp rock edges in their cruising lanes. A big, low, wide tank beats a tall show tank every time.

• Tank size: I would not do one in less than a 6 ft x 2 ft footprint, and bigger is better. They may be "small" as rays go, but they still need room to turn without folding the disc.
• Sand: fine, sugar-sized aragonite is what you want. No crushed coral, no mixed sharp grains. Aim for 2-4 inches so they can settle in.
• Rockwork: keep it minimal and stable. Put rocks on the glass or on a base before sand goes in so a digging ray cannot undermine a pile.
• Flow: moderate overall, but give them calm zones on the bottom. They will avoid blasting current and park where it is comfortable.
• Filtration: heavy and redundant. Oversized skimmer, lots of bio-media, and a mature system. Rays are messy and sensitive at the same time.
• Lid: cover the tank. Rays can and do launch when startled, especially during acclimation.

I like to keep lighting on the softer side and give them shaded areas. They are not a "bright reef" animal, and you will see more natural behavior if they feel secure.

What to feed them

These are predator/scavenger types that hunt small bottom critters. In captivity you are basically teaching them that food comes from you, and the first couple weeks can make or break the animal.

• Best staple foods: chopped shrimp, squid, scallop, clam, and marine fish flesh (not freshwater feeder fish). Mix it up.
• Great "get them started" foods: live blackworms (if you can get clean ones), live ghost shrimp acclimated to salt (short-term), or small live marine shrimp. Use sparingly - the goal is to transition to frozen/prepared.
• Enrichment: soak foods in a vitamin/HUFA supplement 1-2 times a week. Rays on plain shrimp only tend to fade over time.
• How to feed: target feed with long tongs right on the sand. Let them smell it and take it off the bottom. They are not midwater snatchers.
• Frequency: smaller rays do better with smaller meals more often. I start with daily feeding, then adjust based on body condition and appetite.

If a new ray refuses food, do not panic-feed the tank and crash water quality. Keep the environment calm, keep nitrate down, and offer small, smelly items on tongs at the same time each day. Consistency helps.

How they behave and who they get along with

They are mostly chill, but they are still stingrays. They spend a lot of time buried, then cruise the bottom and pounce on food. The big compatibility rule is simple: if it fits in their mouth, it is food, and if it can harass them, it is a problem.

• Good tankmates: calm, non-nippy fish that stay off the bottom and will not compete too aggressively at feeding time.
• Avoid: triggers, large wrasses that flip sand, puffers, angels that pick, and anything that likes to bite fins or tails.
• Bottom competition: skip aggressive bottom feeders (big dottybacks, feisty gobies, large crabs). They will steal food and stress the ray.
• Inverts: most crabs and shrimp are snacks. Snails may survive until they do not. Plan the clean-up crew accordingly.

Feeding time is where problems show up. If tankmates rush the food, the ray will either starve or start slapping and stressing. I have had the best luck feeding fish at one end first, then target feeding the ray at the other end.

Breeding tips

Breeding Urotrygon rays in home aquariums is not common. They are livebearers (aplacental viviparity like many stingrays), so you are dealing with internal fertilization and pups, not egg cases. The hard part is getting a compatible pair, keeping them well-fed long term, and giving them enough space and stability to settle into a routine.

If pups are born, they need the same basics as the adults: fine sand, peaceful tankmates (ideally none), and frequent small feedings. They can be delicate and will get outcompeted easily.

Common problems to watch for

• Not eating after purchase: very common. Often tied to shipping stress, poor holding, or internal parasites. Keep things calm, offer tempting foods, and do not let water quality slide.
• Rapid breathing or constant spiraling: usually stress, low oxygen, ammonia/nitrite, or salinity/temp swing. Check parameters immediately and add aeration.
• Skin issues (raw spots, "burn" marks): typically from coarse substrate, rubbing on rock, or poor water quality. Fine sand and clean water fix a lot of this.
• Tail damage: almost always from nippy fish, tight spaces, or rough handling. Tail injuries can get infected fast.
• Wasting away despite eating: think parasites or nutritional gaps. Rotate foods and consider veterinary/fish health guidance for deworming in elasmobranch-safe ways.
• Stray voltage: rays seem more sensitive than many fish. Use a GFCI and check equipment if you see odd twitchy behavior.

If you keep the sand right, keep the water stable, and make feeding calm and predictable, these rays can do well. The catch is they do not forgive shortcuts, so I only recommend them if you already have a mature marine system and you are comfortable solving problems fast.