Because in the open water of the oceans, not only the herbivorous level of the food chain is on the plankton scale but also the first carnivorous level or level

Because in the open water of the oceans, not only the herbivorous level of the food chain is on the plankton scale but also the first carnivorous level or levels. The small fish that are eaten by the larger fish that we eat are already feeding off carnivores.