Cortez skate

Where they come from

Cortez skates are from the Gulf of California (Sea of Cortez) and nearby eastern Pacific waters. They spend life on sand and muddy flats, often deeper than reef fish, where the water runs cooler and oxygen-rich from upwelling. They bury themselves with just eyes and spiracles showing, waiting for snacks to wander by.

Setting up their tank

Size and footprint matter way more than height. For an adult, I would not go smaller than an 8 x 4 ft footprint (roughly 500-800 gallons). Bigger is better, and round or rounded corners help them cruise without banging into glass.

• Temperature: 55-62 F (13-17 C). You will need a reliable chiller.
• Salinity: 34-35 ppt (1.025-1.026 sg).
• pH: 8.0-8.3. Keep it steady.
• Oxygen: Very high. Oversize your skimmer and add surface agitation or an oxygen cone.
• Turnover: 5-8x per hour through sump. Keep flow broad and gentle. No blasting powerheads.

Substrate should be a soft, sugar-fine aragonite sand, 2-3 inches deep. They bury daily and will rash up on coarse gravel. Rockwork should be minimal, low, and stable. Leave open runway space. Hide heaters in the sump. Every intake and pump needs a foam guard or mesh screen.

Lighting can be dim to moderate. They are crepuscular in my experience, most active at dawn/dusk. Lids should be tight and condensation-proof; skates can splash hard during feeding. Plan water changes like a schedule, not a suggestion: 15-20% weekly kept my nitrate in check with the heavy feeding they need.

What to feed them

Think meaty, marine, and varied. New skates may only take live at first, but you can wean them to frozen with patience and a feeding stick.

• Chopped squid, scallop, clam, mussel
• Pieces of marine fish (silversides, capelin, sand lance) - rotate, do not rely on one species
• Shrimp (shell-on bits for roughage, but not every meal)
• Live or fresh marine worms and amphipods for new arrivals
• Occasional krill for variety

Feed small portions 4-6 times per week rather than giant meals. I target-feed with long tweezers right in front of the spiracles and let them inhale it. If you see them regurgitate later, you fed too much or too warm. Remove leftovers within 5 minutes.

How they behave and who they get along with

Calm, deliberate, and surprisingly quick in short bursts. They spend hours buried, then do slow patrols. They are not bullies, but they will eat bite-sized crustaceans and fish that hang on the bottom.

• Good tankmates: peaceful, coldwater fish that keep to the water column and do not nip (Catalina gobies, some sculpins, temperate basslets).
• Risky: any nippy fish (triggers, puffers, some wrasses) - they go for the wings and spiracles.
• Not with: ornamental shrimp, crabs, lobsters. They are food.
• Other skates/rays: only in very large systems with lots of floor space and extra filtration. Watch for food competition.

They tame down and learn the feeding spot. Use slow, predictable movements. If you must move them, support the body from underneath with both hands in the water. Do not grab the tail or wingtips.

Breeding tips

They lay egg cases (mermaid's purses). Realistically, this is a public-aquarium-scale project, but here is what has worked for me and colleagues with similar skates.

• Sexing: males have claspers; females do not.
• Seasonal cue: slight winter cooling and longer dark period seemed to help pairing.
• Provide smooth egg-deposition panels or coarse plastic mesh near the bottom with gentle flow.
• Incubation: 4-9 months depending on temperature (cooler is slower). Keep 55-60 F with steady, oxygenated flow across the cases.
• Candling: you can backlight to check development. Pull obviously fungused or sterile eggs.
• Hatchlings: start on live marine amphipods, enriched mysis, finely chopped clam. Frequent small feeds and pristine water.

Common problems to watch for

• Refusing food: often stress or too-warm water. Dim the lights, lower to 55-58 F, try live marine worms to jump-start feeding, then switch to tongs and frozen.
• Skin abrasions: usually from rough substrate or rock edges. Switch to finer sand, pad intake guards, and treat secondary infections with vet guidance.
• Heater and pump injuries: keep all heaters in the sump and guard every intake. Skates love to park on warm/humming equipment.
• Low oxygen/overfeeding: heavy, meaty diets burn oxygen and spike ammonia. Overskim, add aeration, and increase water changes.
• Nutritional gaps: head-shakes or poor condition can be diet variety issues. Add vitamin/HUFA soaks and rotate foods. Watch for thiamine deficiency if using a lot of smelt/silversides.
• Parasites (flukes): flashing and gill irritation. Praziquantel is generally the safer route for elasmobranchs, but dose carefully and consult a pro.
• Copper exposure: rapid decline, lethargy, and mucous issues. Avoid any copper-based meds, and test new rock/sand and old tanks before use.

Quarantine new arrivals in a large, chilled holding tank with a pan of fine sand so they can settle. Keep lights low, offer small meals, and observe for two weeks before moving to the display.