The correct answer is: d) Mahseer.
Mahseer is a freshwater fish species of the carp family Cyprinidae. It is highly prized and considered a delicacy in many parts of the world, including Assam. Mahseer is a large fish, with some species reaching lengths of up to 2 meters and weights of up to 50 kilograms. It is a strong and powerful fish, and is known for its fighting ability when hooked. Mahseer is a popular game fish, and is also fished commercially for its meat.
The other options are incorrect. Pangas is a freshwater fish species of the catfish family Siluridae. It is a common fish in many parts of the world, including India. Pangas is not considered a delicacy, and is not fished commercially in Assam. Chital is a type of deer that is found in India and other parts of Asia. It is not a fish, and is not considered a delicacy. Tengara is a freshwater fish species of the carp family Cyprinidae. It is a common fish in Assam, but is not considered a delicacy.