You cannot live off of rabbit as your only protein. You can live off of fish as your only protein, but that’s not what’s being discussed.
A diet that is 100% fish can be toxic to humans. Both Omega-3 and Omega-6 are nessessary for humans but in high quantities they are also linked in liver and heart disease. Nutritionist and health professionals recommend no more than 3 to 4 servings of fish a week.
Ocean fish are also very high in mercury and microplastics.