Ultrastructural and histochemical observations on electroejaculated spermatophores of the palaemonid shrimp, Macrobrachium rosenbergii.

Spermatophores obtained by electroejaculation from mature males of Macrobrachium rosenbergii were studied by light microscopy and by transmission and scanning electron microscopy. Upon electrical stimulation, single spermatophores were usually extruded simultaneously from each gonopore and frequently became firmly adherent to one another forming a compound spermatophore. Individual spermatophores were pod-shaped. 0.5-1 cm long, 2-3 microm in diameter and consisted of a lateral sperm mass, a medial mucus mass, and a noncellular capsule. The capsule was a single-layered PAS-reactive structure composed of fine, intertwining fibrils and almost completely surrounded the sperm and mucus masses. On its outer surface were large. AB-reactive globules of flocculent material partially surrounded by finger-like extensions of a canaliculated reticulum composed of fine, intertwining fibrils. The canaliculated reticulum may permit fluid imbibition by the spermatophore. Forming a central band within the capsule were many small membrane-less AB/PAS-reactive granules. The lateral sperm masses consisted of unistellate spermatozoa embedded in an AB/PAS-reaetive matrix composed of globules of flocculent. AB-reactive material and a highly plastic canaliculated and thread-filled reticulum. The reticulum itself consisted of fine, intertwining fibrils. The threads within the interstices of the reticulum were long, curving structures, 30-36 nm in diameter. The function(s) of the canaliculated and thread-filled reticulum within the sperm mass is not known at this time. The medial mucus mass was similar in fine structure and histochemical reactivity to the sperm mass, except that spermatozoa were lacking. It is apparent that the spermatophore of M. rosenbergii consists of relatively few complexly arranged structural and macromolecular components designed to transport and protect the spermatozoa.