Which one of the following is a true fish as per the biological system of classification?

Q. Which one of the following is a true fish as per the biological system of classification?
a) Silver fish
b) Jelly fish
c) Cuttle fish
d) Flying fish

Answer: Flying Fish

Fish are the gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification.

Fish, the member of the Animalia Kingdom is classified into Phylum Chordata and Vertebrata Subphylum. Fishes poses notochord, tubular nerve chord, paired gills, segmentation of the body parts, post anal tail, ventral heart, and an endoskeleton to be the member of the Chordata. In order to be a vertebrate, it poses backbone. This back bone supports and protects the spinal cord.

All the species of the fish found in the world are classified into the following three groups. They are:

1. Agnatha - jawless fish
2. Chrondrichthyes - cartilaginous fish
3. Osteichthyes - bony fish

•   Ray finned group
•   Lobe finned group