Jeremy Wade is full of fish stories, only he’s not exaggerating when he describes his latest catch. Wade is a big-game angler, constantly in search of freshwater monsters that make sharks seem as docile as dolphins. The host of Animal Planet’s “River Monsters,” Wade plies his skill with heavy fishing equipment and a passion, he admits, that borders on obsession. “You start off interested in variety, and then it’s always about bigger fish, bigger fish, and I became fairly obsessive I think in my late teens and early 20s,” he says. The British-born Wade began fishing for carp. “There was...