government from continuing to use Castle Garden until the Ellis Island immigrant depot was completed. The new registration office on Ellis Island was completed in 1892. In its last year of operation, Castle Garden processed 450,394 travelers, 364,086 of whom were immigrants. When the immigrant-registration depot closed, city officials contemplated converting Castle Garden into an "amusement resort". The New York state government formally transferred Castle Garden to the city government on December 31, 1890. By the next year, city officials had removed the wooden fence around Castle Garden, and they were planning to demolish the various outbuildings around the fort. The New York Naval Reserve's First Battalion considered relocating to Castle Garden at that time, and it subsequently used Castle Garden as a drill hall during the early 1890s. Use as aquarium Castle Garden was the site of the New York City Aquarium from 1896 to 1941. The structure was extensively altered and roofed over to a height of several stories, though the original masonry fort remained. When the fort was converted into an aquarium, the adjacent section of Battery Park was extended into the Hudson River. The interior of Castle Garden contained two circular colonnades, which supported a roof with skylights. Above the center of the fort was a green-and-yellow dome, with a verse of Scripture (Habakkuk 1:15) inscribed into the dome's base. The aquarium could accommodate 10,000 fish and other species. At the center of the ground story was a large circular pool surrounded by six smaller elliptical pools. Fish and other marine species were loaded into the aquarium through a doorway at one end of the fort. The perimeter of the aquarium was originally surrounded by about 100 tanks of varying sizes, placed on two levels. The tanks were up to deep, with plate-glass panes and white-tiled surfaces. By 1907, there were seven large tanks at the center of the ground story, 94 large tanks and 26 smaller tanks on the walls, and 30 reserve tanks. The tanks were supplied by fresh water from the New York City water supply system and salt water from the Hudson River. Salt water passed through two bronze filters, while fresh water passed through two copper filters; the four filters could collectively process over per day. Conversion and opening The New York City government had proposed converting Castle Garden into an aquarium in 1891. The following February, the New York State