Old Sam is said to be a Silver Carp. Rare for that area in North Carolina. Bighead and silver carp, together the "bigheaded carps," are native to China. In North America, the term "Asian carps" is used to refer to the bigheaded carps together with the also-invasive grass carp and black carp, or sometimes to the bigheaded carps alone. Bigheaded carps were imported in the 1970s for aqua- culture and use in sewage treatment. They escaped from captivity, and by the late 1990s had become extremely abundant in parts of the Mississippi River drainage. In the United States, they are an undesirable pest species, and there is evidence of competition with native fishes.
Old Sam is a carp, a fairly common species of bottom feeding fish. This episode mentions he is a silver carp, rare for North Carolina.
The question always arises about how difficult it would be for Howard to renege on his deal with the aquarium. The tank itself would already be a part of the facility, but at a minimum Howard himself would've had to pay for the bronze plaque, transportation both ways, and possibly a fine for the administrative trouble he put them through.