Physiology of Finfish and Shellfish (2+1)

5.2.18. The urophysis (Caudal neurosecretory System)

Most fish also possess a urophysis, a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord. Urophysis consists of neurosecretory cells.

The hormones of urophysis are called “urotensins” and four kinds of them are identified. These are urotensin I, II, III and IV. These are peptides and all the 4 may not be present in the same fish. However, urotensin I and II are commonly found in a fish and their release is controlled by the central nervous system. The exact function of urophysis is still not definitely known. However, the extract of urophysis produced the following effects. Urotensin I: increases the blood pressure of fish but is less potent than urotensin II.

Urotensin II: It is involved in the contraction of smooth muscles such as urinary bladder, causes a marked increase in blood pressure and enhances urine flow.

Urotensin III: It induces the sodium intake across the gills ( osmoregulation ) of gold fish. But effect of this component is not observed in other fishes.

Urotensin IV: It shows activity like antidiuretic hormones of pituitary gland.