Shellfish Breeding and Hatchery Management (2+1)

29.1.3 Ecdysteroids (Arthropod molting Hormones)

The Y organ (Molting gland) secrete the moulting hormone, ecdysone. Ecdysone initiate the molting.

Ecdysone structure was determined from insects, horn and his colleagues isolated and determined the structure of 20 – hydroxyecdysone (20 HE) from the lobster Jasus Lalandei. They demonstrated the identify of the arthropod molting hormone from both insects & crustaceans.

Ecdysteroids and Reproduction:

Some evidence exists that ecdysteroids are involved in crustaecan eggs and embryonic development with RIA detection after HPLC separation, ecdysone, 20HE, ecdysteroid conjugater, and (in some cases) ponasterone A have been identified in follicle cells oocyter, and embryos of various species including shrimp palalmon serratus. Embryonic ecdysteroid concentrations were low after fertilization, but increased rapidly following the appearance of the embryonic Y organ.

The actual function of these ovarian ecdysteroide is uncertain. There are correlation between vitellogenis and increasing hemolymph ecdysteroid is some species but not in stimulatory or inhibitory effects on vitellogenis. The conflicting result are difficult to interpret due to special differences, animal age, and stage in the molt and reproductive cycle, Adiyodi (1985) gives more through discussion.

Ecdysteroids concentration changes have been observed in developing embryos of various species.

These observations support the hypothesis that they are at least partially of embryonic origin, and not entirly sequestered from the mother during vitllogenesis . These embryos, which were spawned at fertilization and in some cases incubated on the female’s obdomen, were without and cytoplasmic connections to the parent. Ecdysteroid concentration were must likely due to endogenous synthesis. A low concentration of ecdysteroids initially deposited in the eggs, and synthesis and secretion by the embryo begins soon after fertilization.

Further evidence for larval ecdysteroid synthesis is the Y organ description in larval crob cancer anthonyi The function of these embryonic ecdysteroids are not know, It is plusible, However, that they are involved in the deposition of embryonic envelops and in embryonic molting.

Female reproduction:

One of the major contraints still facing shrimp culture is control of female reproduction. Reproduction molting are often antagonistic events since both require large energy expenditure and are often mechanically incompatible.

Gonad – Inhibiting Hormone (GIH) :

The primary action of GIH in females apporetly occures during secondary vitellogenesis, the time when the ovary increases dramatically in size due to syntesis and uptake of yolk produced in either tollicle cells or at extraovarian sites.

The stuidy by quackenbush and keeley (1968) sguggests that the target of GIH may be synthesis of golk protein. there are other data, however, that suggest that GIH may inhibit binding and uptake of yolk by the oocyte. Whether the same or different factors are responsible for these activities is unclear. purification and amino acid sequencing of GIH is one of the most active areas of research in crustacean endocrinology.

Mythyl Farnesoate:

Based on endocrine regulation of moliting analogie between crustaean & insects It is responsible to hypothesize that an analog to the insect juvenile hormone (JH)is present in crustuan. The insect JH plays important roles in regulating morphological development & Reproduction.

There are correlations between secondary activity of the MO and vitellogenesis. In the sipider crab, MOs from junvenile females secreted small amount of MF in culture. During the later stages of ovanion development, however, when vitellgeonesis was host pernounced, secretion of MF by the Mo increused to 3.2 ng/gland/hr. At the completion of vitellogenesis, Mo secretion dropped to 1.6 ng/gland /hr. The precise role of Mf in vitellogenesis remains unclear.