This is a fish story. And all of it is true.

It is actually about 2.8 million fish, all dead and preserved in jars, except for the big ones, which are carefully preserved in tanks.

They are all going on a little trip. “Five hundred yards,” said Scott A. Schaefer, who is in charge of looking after them.

“No, not even,” said Steven Warsavage, who is in charge of moving them.

They make up the ichthyology collection of the American Museum of Natural History, ichthyology being the branch of zoology that deals with fish. The move began last week, even as a court fight continued involving residents who oppose the reason for the move: the museum’s $383 million plan for a five-story addition on the Columbus Avenue side of the museum. Opponents fear the effects on Theodore Roosevelt Park, which is on the museum’s grounds.

The museum is relocating the fish to make way for the long-planned addition, to be known as the Richard Gilder Center for Science, Education and Innovation. The center will cover space now occupied by three smaller structures connected to the main section of the museum that are to be demolished. The fish collection has been kept in one of them for more than 70 years.