Which of the following is very difficult to control due to different stages of life cycle showing different susceptibility to chemicals?

Correct option is B

Correct Answer: (b) Lernea sp.
Explanation:
→ Lernea (anchor worm) has a complex life cycle with multiple larval stages, each showing different resistance to treatments.
→ Adult females embed deeply into host tissues, making them difficult to remove.
Information Booster:
→ Affects carp and ornamental fishes commonly.
→ Causes inflammation, ulcers, and opportunistic bacterial infections.
→ Best control involves integrated management and removal of adults.
Additional Information: Argulus and Caligus respond better to standard antiparasitic treatments.