An organism occupying the 3rd trophic level is best described as a tertiary consumer

The answer is: Carnivores
Organisms at the third trophic level are secondary consumers. These secondary consumers prey on the primary consumers which are animals that eat plants or herbivores. Secondary consumers are best described as carnivores because they don't eat plants. They only eat animals that consume plants like cows and chicken.

Aquaculture and fishing are different from each other in many aspects.

Explanation:

Aquaculture can be defined as the process of cultivation of both the aquatic plants and animals, where as Fishing can be defined as catching or harvesting different fishes only.  Aquaculture can be of two types- Marine water and fresh water aquaculture. Aquaculture increased the production of food for the consumption of human and also increase the national import level. Fisheries generally deals with catching and selling fishes. Main point that can be noted is- pearls can be gained only through the process of aquaculture not through fishing.