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Spatial adaptations that maximize a species’ fitness in its local environment, particularly in the form of countergradient variation (CnGV= genotypic influences counteract environmental effects on trait variation) and cogradient variation (CoGV= genotypic influences accentuate environmental plasticity), have been documented in many estuarine and anadromous fishes. However, their prevalence in more oceanic fishes, where extensive gene flow and reduced environmental selection may preclude local adaptation, remains unclear. If oceanic species lack genetic structure, they may be limited in their ability to adapt to global climate change. We examined the potential for adaptation in oceanic fishes by testing whether an oceanic silverside, the California grunion Leuresthes tenuis, displays CnGV in growth capacity and CoGV in vertebral number across a latitudinal gradient as found in estuarine silversides. Common …