Co-founders Chris Conk and Ammon Covino admitted buying spotted rays and lemon sharks from a Florida business to bring to Boise, the Idaho Statesman reported.
They, along with the non-profit organization, will be sentenced Dec. 3 in Key West.
Ammon Covino's nephew, Peter Covino IV, was sentenced Tuesday to 180 days of home detention for obstruction of justice in relation to his uncle's case, the Statesman said.
The day after the co-founders were arrested in February, Peter Covino called the Florida business and attempted to cancel a marine life shipment that Ammon Covino and Conk had ordered.
He also asked the company to delete all emails, text messages and other evidence associated with the order.
Peter Covino said his uncle directed him to make the call.
The Boise Aquarium is the subject of Idaho Humane Society and Idaho Department of Fish and Game investigations, the Statesman said.