Concept:Aquaculture ponds are classified by the material used to construct them.
Explanation:The recognised types of pond in fish farming are the earthen pond, concrete pond, and plastic pond.
Earthen ponds are dug directly into the ground; concrete ponds are built with cement; plastic ponds are made using heavy-duty plastic liners or tanks.
A metallic pond is not one of these standard types.
Although fish can be kept in metal or other containers, such containers are not formally classified as ponds.
Therefore, the option that is not a type of pond is metallic pond.
Answer:A. Metallic pond