Pretty much stop, take a couple steps back, and evaluate why some saltwater fish are extremely aggressive and carnivorous. Because they often have extremely high metabolisms and are extremely active (think lunare wrasse here), or cover great distances of ocean (think sharks) or some fish are both (think marlin/sailfish).
Either way, fish can not eat and eat, without transferring food into energy, without using it up. Fish like anglers and toadfish, simply don't eat very often, when they do.