Common Bleak

Fascinating facts about the Common Bleak

• A single female can lay between 5,000 and 7,000 eggs in multiple batches, deposited on submerged vegetation or shallow areas. The eggs hatch in about 2 to 3 weeks, and the fry initially feed on plankton.
• When water warms to a narrow 14-15 °C window between April and June, the bleak rushes into breeding mode, and males sprout orange-tinged fins and tiny tubercles on their backs. This brief, temperature-driven display underlines how tightly the species ties its reproduction to seasonal cues.
• The common bleak typically reaches sexual maturity at around three years of age.
• The fish lives in large schools and prefers open waters, often in large numbers where an inflow of food from pumping stations or behind weirs occurs.
• In 1656 a Parisian named Jaquin turned the bleak's shimmering scales into "pearl essence", crystalline guanine used for artificial pearls. That tiny biochemical trick shows how a humble fish once helped fashion luxury items, linking nature to human craft.

At a glance

About the Common Bleak

The common bleak (Alburnus alburnus) glides through Europe’s rivers and lakes with an elongated, flat body and a silvery sheen that catches the light. Its pointed head and upward-turned mouth are already distinctive in juveniles, setting it apart from the broader-bodied roach or the short-anal-fin ruffe. Adults reach up to about 25 cm (10 in) and display colourless, pointed fins, while a complete lateral line runs the length of the fish, a hallmark of the Leuciscidae family. In the open waters of streams and lakes, bleak congregate in great schools, often near inflows from pumping stations or behind weirs where food is abundant. Feeding on small molluscs, insects that fall onto the water surface, insect larvae, worms, tiny shellfish and plant detritus, the bleak thrives on the detritus-rich zones of its habitat. Spawning takes place from April to June in shallow shore waters, with females laying 5,000–7,000 eggs on submerged vegetation, while males develop orange-tinged fins and nuptial tubercles. The fry grow slowly on plankton, and the species can even hybridise with other cyprinids such as chub, roach, rudd or bream, an unexpected genetic flexibility that hints at its adaptability in changing ecosystems

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