Answer:
A
Step-by-step explanation:
When an organisms tentatively reduces its own fitness, but rather increasing another organism fitness (the host) with the notion that , the host will carry out reciprocal gesture in near future is called A reciprocal altruism.It was coined by Rober Trivers.
The present scenario is an example of Cleaning Symbiosis.Since the smaller fish gets necessary nutrients from the larger fish,with the reciprocal act of cleaning its mouths, the smaller fishes ensured good health or lack of infections through removal of parasite,in a symbiotic relationship. While enjoying good nutrient in return.