Question

Which one is a true fish?
A) Cuttlefish
B) Dog fish
C) Jellyfish
D) Silverfish

Answer 1

True fish are also known as fin fish or finfish to distinguish them from the other aquatic life harvested in aquaculture or fisheries. They have long fins which enable gliding for a large distance, and they have streamlined bodies with scales. A true fish belongs to super class Pisces and Phylum Chordata under the class Tetrapoda.

Complete answer:
A true fish belongs to phylum Vertebrates and Chordates and they have backbone. The notochord present in them during the embryonic development is replaced by the backbone. They have a single chambered heart and belong to the class Pisces. They have fins for propulsion and breathe through gills.

Cuttlefish falls under the phylum Mollusca and is a marine animal or cephalopod. Some members of phylum Cnidaria in medusa stage have the common name as Jellyfish. They belong to the invertebrate phylum Coelenterate. Silver fish is a wingless insect and is small in size. Silver fish is a wingless insect in the order of Lepsima or Thysanura. Hence, they do not fall under the category of true fish. Dog fish is the common name for Scoliodon. They are a type of shark which is a cartilaginous fish under class Chondrichthyes of phylum Chordata.

Hence, the correct answer is option (B).

Note: Cartilaginous fish have their skeleton made up of cartilage, instead of bone. All rays (southern stingray), sharks are cartilaginous fish. They lack swim bladders. Buoyancy in water is maintained by the oils store in the liver. Their tails are heterocercal in nature and they lack operculum.