During the first half of the 20th century, the Departmental collections only comprised about 20,000 lots. Curatorial operations underwent renewal during the 1960s under Donn Rosen's guidance. With support from NSF, about half of the space currently occupied by the Department was either constructed or renovated. The existing collections were moved and transferred to 40% isopropanol. Since Rosen's renewal, the collection has expanded to approximately 2,000,000 specimens, 200,000 lots, 35,000 skeletons, and 500 types. Most of the increase is in marine fishes and freshwater fishes from the eastern United States. In the early 1980s, an additional facilities grant was awarded by NSF, and the collection area was doubled and renovated, expanding the space occupied by the Department to 15,000 square feet. The Ichthyology section then occupied some 15,000 square feet of office, lab, and storage space on the first and second floors, and a mezzanine floor, of three separate but contiguous buildings in the Museum complex. With additional NSF support (1990-1992), alcoholic specimens were transferred from isopropanol to ethanol, large specimen storage and dry skeleton collection space were expanded, and all catalog data was entered into a computerized database. At the time of the 1980s reorganization, the Museum made available additional space to the Department. By 1995, growth of the collections elevated the ranking of the department to fourth of eight among major international centers (Poss & Collette, Second Survey of Fish Collection in the United States and Canada, Copeia 1995(1):48-70), trailing only the collections of the Smithsonian Institution's National Museum of Natural History, The University of Michigan's Museum of Zoology, and the California Academy of Sciences in terms of absolute collection size.
In 1997, the Department underwent a $3.5 million rennovation as part of the construction of the Rose Center for Earth and Space, which provided significant upgrade of the department's offices and labs and added significant new storage capability and a classroom. As a result, the Department of Ichthyology currently occupies approximately 17,000 square feet of office, laboratory, and storage space on four floors of two adjacent buildings.