Gonad stimulation in Crustacea: an interspecies approach

Macrobrachium rosenbergii, a prawn that is continuously reproductive, was used as a source for factors to stimulate gonad activity in females of the reproductively stringent shrimp, Penaeus vannamei. An in vitro bioassay was developed to test the activity of the prospective factors prior to their administration into the recipient. An organ culture of pre-vitellogenic, early-vitellogenic and late-vitellogenic ovaries of M. rosenbergii females was established. The ovaries were cultured in the presence of both ³H-Thymidine and 35S-Cysteine, which showed a linear incorporation (up to 8 hr) into DNA and proteins, respectively. The ratios of ³H to 35S incorporated decreased in the order: pre-vitellogenic > early-vitellogenic > late-vitellogenic.
One of the factors tested during the in vitro bioassay was methyl farnesoate known to be synthesized by the mandibular organ of crustaceans. This molecule is the unepoxidated form of the insect juvenile hormone III, which is a gonadotropin in insects. To study the presence and synthesis of methyl farnesoate in M. rosenbergii, the mandibular organ was identified and cultured in the presence of methyl-³H-methionine. Radiolabelled methyl farnesoate was extracted and quantitated from cultured glands and a culture media made of females. The concentration of methyl farnesoate in the hemolymph was determined using normal phase HPLC. Hemolymph from females contained 24 + 13.1 ng/ml of methyl farnesoate.