Topsmelt Silverside

Fascinating facts about the Topsmelt Silverside

• A 37-centimetre (15-inch) topsmelt can glide just below the surface, often staying in the top 9 metres (30 ft) of water. Its bright green dorsal fins contrast with the silvery body.
• When the tide pushes into salt-evaporation ponds, this fish tolerates salinities up to 80 ppt.
• From March through October, topsmelt gather under the cover of night to lay eggs over submerged plants at around 30 ppt salinity and 13–27 °C (55–81 °F).
• Juvenile topsmelt are practically invisible, with translucent bodies and three rows of pigmented scales on their backs, while adults develop a diet that includes sand and gravel, a sign they feed along the bottom. This shift from planktonic to benthic feeding highlights a flexible life-stage strategy that lets them exploit multiple food webs.
• When chased by larger predators like mackerel or jacks, topsmelt often leap out of the water, turning a predatory chase into an aerial escape. Their sudden jumps provide a dramatic snapshot of predator-prey dynamics and remind us that even small fish have clever tricks to survive.

At a glance

About the Topsmelt Silverside

The topsmelt silverside (Atherinops affinis) glides through Pacific waters with a sleek, dorsally-flattened silhouette that can reach 37 cm (15 in). Its bright green first dorsal fin and silvery flanks create a striking contrast, while a golden-yellow gill cover hints at its delicate physiology. The fish’s pointed head, small eyes, and terminal, extendable mouth are lined with tiny forked teeth, and its pectoral fins bear 13 rays. Juveniles are almost translucent, marked only by three rows of pigmented scales that later scatter along the caudal peduncle, a subtle reminder of their transition from nursery to adulthood. A pelagic schooler, the topsmelt occupies a mosaic of habitats, from estuarine mudflats and kelp forests to the shadow of pier pilings and even hypersaline evaporation ponds exceeding 80 ppt. In spring and summer it migrates into estuaries, spawning at night among submerged vegetation when salinity hovers near 30 ppt and temperatures sit between 13 °C and 27 °C (55 °F–81 °F). After hatching in deeper water, larvae drift upstream, while juveniles, primarily zooplankton feeders, frequent freshwater zones before shifting to benthic foraging as adults, gulping algae, chironomid larvae, amphipods, and even sand and gravel. A surprising behavior is their dramatic leaping, a frantic escape from larger predators such as mackerel and jacks, sending silvery arcs that briefly punctuate the surface before the school vanishes beneath the waves

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