Changes

While glass containers improved and were getting larger by the late 19th century, particularly as more major cities in Europe and North America began to build aquariums, the general approach to keeping fish did not change much during the late 19th century. It was only in the early 1900s that more innovations made it possible to dispense with plants all together. The was called the "balanced aquarium" approach of keeping the number of plants and fish balanced. Charcoal-based filtration and air pumps were invented to allow oxygen to be pumped into tanks and this became the primary way in which tanks kept fish throughout the early 20th century. <ref>For more on early filter technologies and pumps, see: Delbeek, J.C. & Sprung, J. (2005) <i>The reef aquarium science, art et technology.</i> Coconut Grove (Florida), Ricordea Publishing.:</ref>

In the 1950s, the undergravel filter was introduced, which was a way to pump air through the base of the tanks (or the gravel acting as the base of the aquarium). From the 1950s and into the 1970s, more varieties of fish were also introduced at aquariums to further peak the interest of the public. During the 1960s, dolphinariums were developed in North America first and then later Europe, where this proved to be very popular in drawing larger crowds to aquariums and what soon developed as larger private safari and other parks. The 1960s also saw the development of new sealant technologies that allowed glass only rather than glass and metal aquariums to be developed.<ref>For more on the modern aquarium and its development, see: Hemdal, J.F. (2003) <i>Aquarium fish breeding.</i>Hauppauge, N.Y, Barron’s, pg. 8.</ref>

Filters continued to be improved, including the wet-dry filter in the 1980s, that allowed more exotic corals to be kept more easily. With the environmental movements of the 1970s, aquariums, similar to zoos, increasingly began to focus towards conservation efforts. Major oil spill disasters, for instance the Exxon Valdez, led rescued sea otters and wildlife to be transported to aquariums such as the Shedd Aquarium in Chicago. In fact, for decades, was the largest aquarium anywhere and pioneered the development of permanent saltwater fish displays. Other major aquariums, such as the National Aquarium in Baltimore, have largely re-branded themselves as research and conservation facilities, although public display helps to fund their activities and educate the public.<ref>For more on the role of aquariums today in marine and freshwater conservation, see: Helfman, G.S. (2007) <i>Fish conservation: a guide to understanding and restoring global aquatic biodiversity and fishery resources.</i> Washington, Island Press.</ref>