Ninespine Stickleback

Fascinating facts about the Ninespine Stickleback

• A ninespine stickleback only grows to about 12.5 cm long and typically lives just three years.
• Although its name suggests nine spines, the dorsal spine count actually ranges from seven to twelve, with nine being the most common, a reminder that nature loves variation.
• From April through July, the male builds a tiny nest on a waterweed stalk, suspending it roughly an inch above the bottom, then guards the eggs and fry until the young develop their own spines and are driven away.
• Freshwater pond populations can keep their metabolism humming across a 13 °C window, from 6 °C up to 19 °C, by lowering their standard metabolic rate, a flexibility that helps them survive temperature swings that would stall other fish.
• When dissolved oxygen drops, ninespines cannot gulp air like some fish; instead they perform aquatic surface respiration, rising to the oxygen-rich top millimeter of water at higher oxygen levels than their brook-stickleback cousins.

At a glance

About the Ninespine Stickleback

The ninespine stickleback (Pungitius pungitius) is a diminutive, elongated fish that rarely exceeds 12.5 cm and lives about three years. Its sleek body tapers to a narrow, fan-shaped caudal peduncle, and unlike its three-spined cousin it lacks scales, bearing instead a patch of tiny bony plates along the lateral line at the narrowest point of the tail. The dorsal region is marked by seven to twelve spines, nine being most common, while the upward-pointing mouth, grey-olive back, and silvery flanks dotted with irregular dark bars give it a cryptic appearance among the thick submerged vegetation it favors in streams, lakes, ponds and rivers across Eurasia and North America. During the breeding season from April to July, males construct a floating nest on waterweed, display a striking black patch around the pelvis, and turn the pelvic spines white, then guard the eggs and newly hatched fry until the juveniles develop their own spines, at which point the devoted male drives them away to fend for themselves. Beyond its modest size, the ninespine stickleback is a physiological marvel. It is euryhaline and eurythermal, thriving in both freshwater and marine settings and tolerating temperatures from six to nineteen °C. Freshwater pond populations have shown the ability to lower their standard metabolic rate, allowing survival under less favorable conditions, while marine counterparts maintain a higher hepatosomatic index and reduce metabolic rates in colder water. Unlike many fish, it is a physoclist and cannot gulp air; instead, it resorts to aquatic surface respiration when dissolved oxygen drops, rising to the oxygen-rich surface layer, a behavior that reveals its unique adaptation to hypoxic stress. These traits make the ninespine stickleback a compelling subject for studies of phenotypic plasticity and genetic divergence, as researchers continue to unravel how isolated populations, some less than 11,000 years old, navigate the delicate balance between environmental change and evolutionary resilience

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