This essay looks at how the practices of Soviet fisheries science, focusing on the Caspian Sea region, changed in the late 1920s and 1930s. What was new in the 1930s was not so much increased emphasis on industrialized fisheries or the need for practical science, which had always been present in fisheries science. What stood out most, instead, was the marked shift to prediction as the preeminent goal of scientific activity driven by the concrete needs of a planned economy. The shift had important consequences for the practices of fisheries science and fish as scientific objects. New research priorities pushed by the need to plan economies of fishing entailed different ways of seeing and representing both fish and time.