A fish dive, or just a “fish,” is a classical ballet term describing a step where the ballerina is in a retiré position and held low to the ground by a male dancer. A fish can be done simply from arabesque where the male places his hands around the ballerina’s waist and under the thigh of the arabesque leg, then lifts and bends his back leg into the fish position. It is also often done from lifts over head or from a shoulder sit.
Fishes, or fish dives, are seen quite often in classical partnering and pas de deuxes. It is considered an intermediate partnering step.