Explanation: Perch is a type of fish which feed on zooplankton, so it belongs to secondary consumer in the trophic levels. In aquatic ecosystem, plants are the producer which contains 50,000kcal of energy. When these plants are eaten by primary consumer i. e. zooplankton, so only 10 % of energy is transferred about 5000 kcal. When zooplankton are eaten by perch fish, so 10 % energy is transferred again i. e. 500 kcal.
