Common names: silverside (English), plateadito (Espanol)
Atherinella crystallina (Jordan and Culver 1895)
Blackfin silverside, Presidio silverside
Head length 23.4% of SL; top of head profile ~ straight; sensory system on snout with L shaped furrows at front; top jaw extendible; first dorsal short, not reaching base of second dorsal, front spines longest, II-VI, its origin behind origin of anal; second dorsal margin straight to slightly concave, front rays not very long, its base ends before base of anal; anal I, 16-27 (usually I, 21) rays, no scales on bases of first few rays, rear margin straight, with anterior rays longest; pectoral fin straight to curved, not reaching anus; 35-49 (39) lateral line scales, 6-10 transverse rows of scales; large scale at side of pelvic fin base.
Fleshy base of pectoral darkly pigmented; male with dark-tipped pelvics (no pigment in female); first dorsal fin, front of second dorsal and front of anal dusky, darker in males than females; dark stripe along top of back; heart-shaped dark pigment patch over rear of brain; stripe along side sometimes silvery, not constricted on tail base, width < ½ eye diameter; airbladder has window-like appearance through belly muscles.
Size: 10 cm.
Habitat: Usually in freshwater but also in estuaries.
Depth: 0-10 m.
Restricted to the SE Gulf of California.