Tuna and trout are high in protein, but trout may have more vitamin D and omega-3s. Design by Verywell Health; Getty Images Tuna is generally higher in protein and lower in calories, making it ideal for lean, high-protein diets. Trout offers more vitamin D and omega-3s, supporting heart, brain, and bone health. Trout is generally low in mercury, making it a safer choice for frequent consumption.