Crucian Carp

Fascinating facts about the Crucian Carp

• A 64 cm male crucian carp holds the record for length, far exceeding the typical 15 cm size most individuals reach.
• During a frozen winter, these fish can stay alive without oxygen for up to 140 days by turning muscle tissue into ethanol and simply spilling it into the water.
• When predators are around, crucians grow a deeper body shape that makes them too bulky to swallow, but this comes at the cost of slower growth and weaker immune defenses.
• The British rod-caught weight record was set on 30 October 2024 when Adam Broodbanks landed a 2.212 kg (4 lb 14 oz) crucian, edging out the previous 2.155 kg record from 2021.
• In the Netherlands, anglers have photographed a typical specimen measuring 54 cm and weighing 3 kg, showing how much larger these pond fish can get compared with the average.

At a glance

About the Crucian Carp

The crucian carp (Carassius carassius) glides through the quiet shallows of northern European lakes, ponds, and slow-moving rivers, its body a shifting palette of golden-bronze in youth to a dark green back, deep bronze flanks and gold belly in maturity, capped with reddish or orange fins. Typically about 15 cm long and rarely over 2 kg, the species can reach a remarkable 64 cm and 3 kg in exceptional males, its convexly rounded fins a reliable field mark that sets it apart from the concave-fined goldfish hybrids. Beneath the placid surface, crucians display a suite of adaptive behaviours: when predatory fish loom, they morph into a deep-bodied form that resists swallowing, yet this shape comes at a cost, curbing immune function and slowing growth. Their diet is opportunistic, cleaning pond ecosystems by consuming excrement and organic detritus, thereby preventing nitrogen overload. The most astonishing of their adaptations is a winter-time metabolic shift that lets them survive months under ice-sealed, anoxic water by fermenting glucose to ethanol, excreting the alcohol into the water and avoiding the lethal buildup of acidic by-products, a rare vertebrate feat that can endure for up to 140 days in the lab.

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