$(a)$ What is composite fish culture system?
$(b)$ Mention one merit and one demerit of this system.

(N/A) Composite fish culture is a method of culturing five or six species of fish,both indigenous and exotic,together in a single fish pond. These species are selected such that they do not compete for food among themselves due to their different feeding habits.
$(b)$ Merit: It allows for higher fish yield as different species utilize different zones of the pond and different food sources.
Demerit: $A$ major problem is the lack of availability of good quality fish seed,as many species breed only during the monsoon season,and wild-collected seeds often contain a mixture of unwanted species.