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How large do three-spined sticklebacks grow?

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Lined seahorse (Hippocampus erectus) — gasterosteiform Lined seahorse (*Hippocampus erectus*).

The three-spined stickleback (Gasterosteus aculeatus) typically grows to a length of 5 to 10 cm (2 to 4 inches).1

While the broader family of sticklebacks (order Gasterosteiformes) can reach a maximum length of approximately 18 cm (7 inches), the three-spined species remains within the smaller 5 to 10 cm range.1