VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

REPRODUCTIVE PHYSIOLOGY OF FISH

Endocrine glands

• The endocrine glands have been defined as being ductless glands, since they release their secretory product directly into the blood or lymph. Mammalian endocrine glands are well advanced and well studied. But fish endocrinology is limited to the work on its influence on chromatophores, action of sex cells, function of pituitary and thyroid and control on migration.

The pituitary glands

• The pituitary glands occupies the same central part in the endocrine signaling system of fish that it has in mammals. One ventral down growth of a neural element from the diencephalons called the infundibulum to join with other. It is located below the diencephalons behind the optic chiasma and anterior to saccus vasculosus and attached to the diencephalons by a stalk. The pituitary is an oval body and is compressed dorsoventrally. The size of sexually mature platfish has a mean anterior length of 472.9 micra.
  • Adenohypophysis
    • The cells of pituitary secrete hormes and hormones are stored in gradular present the cytoplasm. The cells are, therefore, classified on the basis of staining properties of granules of these cells. Chromophilic cells which take acidic stain are called as acidophils whereas the chromophilic cells which bound basis dye are called basophilic cells and the cells which do not take any stain are called chromophobs.
  • Neurohypophysis
    • It is comprised of connective tissue neuroglia cells and loosely tangled network of nerve fibers. These nerve fibers are scattered horizontally along the dorsal part of the adenohypophyais and run vertically which are generously inter spread with granular material large irregularly shaped amorphous masses and large nuclei.
  • Hormones of pituitary
    • There are seven various hormones secreted by pituitary but it is generated agreed that one cell type-one hormone concept is correct the different hormones secreting cell are not localized in specific region.
      • Thyrotropin activates thyroid
      • Adrenocorticotropic hormones activate adrenal cortex
      • The gonadotropin FSH and LH
      • Growth hormes somatotropin.

Thyroid gland

• The thyroid gland consists of a large number of follicles lymph sinuses venules and connective tissues. The follicles are round oval and irregular in shape. Epithelical cells are of two types.
  • Chief cells, which are columnar in shape having oval nuclei and clear cytoplasm
  • Collid cells, which possess droplets of secretary materials
• Adrenal cortical hormone
  • These are (i) mineral corticoids concerned with fish (ii) dlucocorticoids which regulates the carbohydrates metabolism. Intramusclar injection of corticosteroid compound to the oyster causes increase in blood sugar level thus shows control on carbohydrate metabolism.
• The sex glands as endrocrine organs
  • The sex hormones are synthesized and secreted by specialized cells of the ovaries and testis. The release of sex hormones are under the control of mesoadenohypophysis of pituitary. In fishes, these sex hormones are necessary for maturation of gametes and in addition secondary sex characteristics such as breeding tubercles colouration and the maturation of gonopodia.
• Pineal organ
  • It is situated near the pituitary inspite of being a photoreceptor organ the pineal organ shows endrocine nature of doubtful function. Removal of pineal from Lebistes sp. causes reduced growth rate anomalies in the skeleton pituitary and corpuscles of stannius.