Step 1: Understanding the Concept
Interspecific interactions can be mutualism, competition, amensalism and predation.
Step 2: Apply
Flamingos and resident fishes both feed on zooplankton in the same area. Both are harmed because the food is limited.
Step 3: Result
This is competition.
Final Answer:
The interaction between flamingos and resident fishes is competition.
\[ \boxed{\text{(B) }\text{competition}} \]