To clear some of it up. Bruchac is right. Fisher and Fishercats are the same species. Martes pennanti is the latin name and they are a member of the mustelid family which also includes mink, weasels, wolverine, skunk, and badgers. Adult males can weigh up to 30 pounds although 20 pounds is more common.
Females are about half the size of males.
They eat mostly smaller mammals ranging up to rabbits. They are one of the few animals that successfully prey on porcupines. They will eat your cat if you leave it outside. They are fairly common throughout New England but are very elusive and rarely seen. They are not vicious animals, they are efficient predators.