In the ocean it's a fish-eat-fish world teaming with predators.
Some fish, however, feed solely on nourishing plankton and other sea vegetables which grow in abundance at their favored locales, while constantly vigilant against the more aggressive and carnivorous varieties of sea life.
There are only two laws these fish must obey, lest they soon perish, individually or as a species: survival and procreation, or survival until procreation.