In an ecosystem, if a fish is feeding on zooplankton, it is a:

Secondary consumer

The correct answer is Option (3) → Secondary consumer 

• Producers: Organisms like plants or phytoplankton that produce energy via photosynthesis.
• Primary consumers: Herbivores or organisms that eat producers (e.g., zooplankton eating phytoplankton).
• Secondary consumers: Organisms that eat primary consumers (e.g., fish eating zooplankton).
• Tertiary consumers: Organisms that eat secondary consumers (e.g., bigger fish or birds eating smaller fish).

In this question the fish is feeding on zooplankton. Zooplankton are primary consumers because they feed on phytoplankton (producers).So, the fish is one level up → it is a: Secondary consumer