Physiology of Finfish and Shellfish (2+1)

2.3.3. Structure of the kidney

A pair of kidneys lies above the alimentary canal close to the vertebral column. In teleosts, the kidneys are elongated structures usually divided into 2 parts called the head kidney and the trunk kidney. However, in several species, these parts are not demarcated externally. Kidneys of marine teleosts can be divided into 5 types as described below.

Type I: 2 kidneys are completely fused and there is no distinction between head and trunk part of the kidney. This is seen in the members of the family clupeidae.

Type II: Head and trunk regions of the kidneys are clearly demarcated as they are fused in the middle and posterior regions only. Eg. Marine catfishes and eel.

Type III: The kidneys are fused in the posterior region only and the head and trunk potions are clearly demarcated. This is seen in most of the marine fishes belonging to Mugilidae, Belonidae, Scombridae, Carangidae and Pleuronectidae.

Type IV: Only the extreme posterior parts of the kidneys are fused. Head and trunk regions cannot be distinguished as in the sea horse and pipefish.

Type V: There is no fusion and the kidneys are completely separate as in Family Lophidae, Lophius sp (Goose fish).