Out of all the given choices regarding the question about which tuna species is the smallest, the correct answer is letter D or Bonito. Before we discuss Bonito, let’s discuss the other three choices first. Albacore tuna can grow up to 4 feet in length and can weigh up to 80 pounds, bigeye tuna can grow up to 98 inches or 8 feet in length and can weigh up to 400 pounds and Atlantic bluefin tuna can grow up to 8.2 feet in length and can weigh up to 551 pounds. This leaves us with Bonito tuna which can grow up to 3 feet in length and can weigh up to 76 pounds. From the given information, we can now say that the smallest tuna species among all the given choices is Bonito.