The lemon tetra is one of the deeper-bodied tetras, contrasting with slender, torpedo-shaped relations such as the cardinal tetra and the rummy nosed tetra, whose approximate body shape when seen from the side is that of a lozenge,(often referred to as a diamond, is a form of rhombus). The basic body color of an adult specimen is a translucent yellow, with a pearlescent lustre emanating from the scales in particularly fine specimens. The dorsal and anal fin of the fish are marked with black and yellow: specifically, the anal fin is hyaline (glass-like appearance), with a black outer margin, the anterior three or four rays being an intense, acrylic lemon-yellow in hue, while the dorsal fin is principally black with a yellow central patch. The tail fin is mostly hyaline but in fine specimens (particularly alpha males) acquires a gunmetal-blue lustre. The pectoral fins are hyaline whilst the pelvic fins are translucent yellow, becoming more solidly and opaquely yellow with black posterior edges in fine specimens (again, alpha males are particularly notable in this regard). The eye is a notable feature of this fish, the upper half of the iris being an intense red, in some specimens almost gemstone-ruby in appearance. The colour of this part of the iris is an indicator of the health of the fish: if this red colouration fades, or worse still turns grey, then this is an indicator of serious disease in the fish. In common with many characins, the lemon tetra possesses an adipose fin. This fin may acquire a black border, particularly in males, though this is not a reliable characteristic. Black areas of colouration on adult fishes frequently acquire a glossy sheen, enhancing the beauty of the fish.