The Sexuality of Tropical Deepwater Shrimps (Decapoda: Pandalidae)

Abstract

Morphometric studies were carried out as part of resource assessment surveys on deepwater pandalid shrimps in both the northern and southern tropical Pacific Ocean. Previous works have suggested that pandalid shrimps, including those of some tropical species, are typically protandrous hermaphrodites. In this study, however, measurements of certain male secondary sexual characteristics were positively correlated with shrimp size. There was no evidence of degeneration of these characteristics in larger individuals as would be expected with protandrous hermaphrodites. We conclude that shrimps of the tropical pandalid species examined are dioecious and that sex reversal does not occur. Sex reversal in pandalid shrimps was first noted in Pandalus danae (Berkeley, 1929) and, since that time, has been reported for a large number of exploited pandalids from northern temperate waters including P. jordani and P. borealis (Butler, 1964). Butler stated that, with one or two known exceptions, all pandalid shrimps so far investigated were protandrous hermaphrodites. The usual pattern in hermaphroditic pandalid shrimps is for individuals to mature and function first as males and, at two or three years of age, to change sex and function as females. During the change in sex, the appendices masculinae on the endopods of the second pair of pleopods of the male degenerate during a series of intersex or transitional stages, until these structures are entirely lacking in females. Deepwater pandalid shrimps are also widely distributed in the tropical Pacific Ocean, including Hawaii (Clarke, 1972; Struhsaker and Aasted, 1974), Guam (Wilder, 1977), New Caledonia (Intes, 1978), Fiji (King, in press), Tahiti (Anonymous, 1979), Western Samoa (King, 1980), Vanuatu, west of Fiji (King, 198 la), Tonga (King, 1981b), Papua New Guinea (King, 1982), and the Northern Marianas (Moffitt, 1983). Some species, particularly of the genus Heterocarpus, are found in sufficient abundance to stimulate interest in commercial exploitation (King, 1981c). Shrimps of several of these species including H. ensifer (Clarke, 1972), H. ensifer and H. laevigatus (Wilder, 1977), and H. sibogae and H. laevigatus (King, 1981a) were thought to be protandrous hermaphrodites similar to temperate pandalid species. During studies on the biology and commercial potential of deepwater shrimps in Fiji and the Marianas, at least thirteen different species have been found (Table 1). This paper examines the morphometry and the sexuality of five species which were obtained in sufficient numbers and over a wide size range. The species examined were Plesionika longirostris, H. ensifer, H. sibogae, H. gibbosus, and H. laevigatus in Fiji and P. longirostris, H. ensifer, and H. laevigatus in the Marianas.