Paddlefish

Polyodon spathula is among the most unusual freshwater fishes on Earth — a living relic of an ancient lineage, its most striking feature being the enormous, paddle-shaped rostrum that can extend to one-third of the fish's total body length. This rostrum is not used for probing substrate but is densely packed with ampullary electroreceptors that detect the electric fields produced by concentrations of zooplankton, which the fish engulfs by filter-feeding with its enormous gaping mouth. It is native to the Mississippi River Basin and associated large waterways.

In the aquarium or pond setting, Paddlefish are exceptional display animals but present extraordinary demands: they grow to 150 cm, require enormous volumes of clean, cool, well-oxygenated water, and must be maintained on continuous zooplankton or fine-particle suspended foods. They cannot be adequately housed in any standard home aquarium and are fundamentally pond or public-aquarium animals.

They are offered here for specialist pond keepers and public display facilities with appropriate scale and infrastructure. Their peaceful, filter-feeding nature contrasts dramatically with the other large North American species in this catalog, and they rank among the most remarkable living freshwater fishes.

Water: 10–25 °C, pH 6.5–8.0, moderate hardness; very high oxygen, strong flow, enormous volume. Tank: 5000 L absolute minimum — large outdoor ponds or indoor public-scale facilities required. Feeding: Dense zooplankton culture, live Artemia in quantity, fine-particle slurries; filter-feeding specialist. Breeding: Requires cold-water wintering and large river-scale spring flooding conditions — not captive-achievable. Compatibility: Entirely peaceful filter feeder; avoid with very rough or active species that may damage the rostrum.