Induced spawning or hypophysation

Introduction:

• Refers to the injection of mature brood fish with inducing agents to enable them to spawn.
• The indigenous major carp and Chinese carp breed naturally only in the flowing water of the rivers during the monsoon floods.

b. Basic principle:

• The basic principle is to inject the fish with exogenous hormones including PG or HCG.
• These hormones can replace the hormones normally secreted by the hypothalamus or pituitary gland and directly stimulate the gonad.
• Other exogenous hormones like LHRH or LRH-A can take the place of GnRH released by the hypothalamus, to further accelerate the secretion of gonadotropin and stimulate spawning.

c. Inducing agents

• Extract of Pituitary gland (PG), human chorionic gonadotropin (HCG), ovaprim, ovulin, and various gonadotropin-releasing hormones analogs (LHRH).

i. Pituitary gland extract (PG):

• Is important for stimulating the maturation and ovulation of fish.
• The pituitary gland secretes two gonadotropins, the follicle-stimulating hormone (FSH) and the Luteinizing hormone (LH).
• FSH causes the growth and maturation of ovarian follicles in females and spermatogenesis in the testes of males while LH helps in transforming the ovarian follicles into corpora lutea in females and promoting the production of testosterone in males.
• The pituitary gland can be collected from freshly killed matured fishes.
• The injection volume is controlled at 2-3 ml for each brood fish.

Collection procedure:

• Take the head of a freshly killed fish and give fine incisions on the scalp with a hand saw.
• Remove the scalp and clean carefully the grey matter and fatty substances lying over the brain.
• Lift out the exposed brain carefully towards the anterior side of the head.
• Collect the PG using fine forceps which will be left behind on the floor of the brain box.
• Keep the gland in a watch glass and use fresh and if not preserved.
• Keep the gland in absolute alcohol/acetone immediately after collection for defeating and dehydration.
• Wash the gland after 24 hours with absolute alcohol/acetone and keep it again in fresh absolute alcohol/acetone contained in dark-colored bottles.
• Store the bottle at room temperature or in refrigeration.
• For dry storage, dehydrated PG is dried on a piece of filter paper for 15-20 minutes and then stored in a tightly sealed, labeled small bottle.
• Preserved PG can be used within 2 years of preservation.

Extraction preparation:

• Take the PG from the fish of matching weights.
• Place the PG into the mortar or tissue grinder.
• Grind the PG with a pestle until it is pulpy mass.
• Wash the PG into a test tube with 1mm distilled water or saline solution.
• Place the test tubes into the centrifuge for 5 minutes at 2000 rpm.
• Remove test tubes from the centrifuge.
• Draw up the liquid portion from the test tube into the hypodermic needle, leaving the pulp of the gland in the bottom of the test tube.
• Calculate the required dose and inject the fish ( 2-3 ml for each brood fish).

ii. Human chorionic gonadotropin (HCG)

• Pure gonadotropin hormone extracted from the urine of pregnant women and contains LH and FSH.
• Only one injection of HCG is required to stimulate egg release from female fish.
• The dose rate is 400-1000 I.U of HCG to 1 kg of female and 150-400 I.U of HCG to 1 kg of male brood stock.

iii. Luteinizing releasing hormone-analogue (LRH-a):

• Is a synthetic hormone made up of different amino acid chains.
• It helps raise the level of gonadotropin secretion.

iv. Ovaprim and Ovulin:

• Synthetic hormone is used with LRH-a to control the release of the excess hormone.
• Very effective on Indigenous major carp.