The greatest differences between sardines and tuna include their size and families. Sardines are small fish from five different genera that only reach about 12 inches and 4.5 pounds at their largest, but tuna can weigh anywhere from 3 pounds to 1,500 pounds and measure up to 15 feet long. Tuna also come from five different genera, but they do not share any of the same families as sardines. These massive differences make it easy to tell these creatures apart. We’re going to dig deep into five differences between them to show you just how unique these fish are despite both being popular foods for people.