Meeting Abstract

1.7  Monday, Jan. 4  Loss of hypo-osmoregulation in a land-locked population of the shrimp Macrobrachium amazonicum CHARMANTIER, G.*; CHARMANTIER-DAURES, M.; ANGER, K.; Univ. Montpellier 2, France; Univ. Montpellier 2, France; AWI, Helgoland, Germany guy.charmantier@univ-montp2.fr

Two separate populations of this shrimp, from the Amazon delta (A), and from the Pantanal (P), were compared as to their ontogeny of osmoregulation and ecology. Adult A shrimps live in brackish and fresh water (FW) habitats. Their ovigerous females presumably migrate down river, so that hatching occurs close to estuarine waters, where early larval development occurs. Early juveniles later migrate back to FW. The P shrimps, by contrast, spend their entire life cycle in FW. In the A population, tolerance of FW occurred temporarily in the zoea I stage and, again, after metamorphosis. All stages tolerated sea water (SW), being hyper-osmoregulators at salinities <17 ppt, and hypo-regulators at higher salinities including SW. The ability to hyper-regulate was temporarily high in the zoea I, lower in the subsequent larval stages, and increasing again after metamorphosis. Hypo-regulation was efficient throughout their ontogeny, particularly in the late larval and early juveniles stages. In the P population, all stages tolerated FW. Saline waters up to 25 ppt were tolerated by all stages, but mortality was high in SW, reaching 100 % in adults. All stages were hyper-osmoregulators at salinities <17 ppt, with a high osmoregulatory capacity in FW. In contrast to the A population, all stages were osmoconformers at salinities >17 ppt. In conclusion, these results show a close relationship between ontogenetic changes in osmoregulation and migratory patterns of the A population. Among the differences in salinity tolerance and osmoregulation observed between the two populations, the loss of the ability to hypo-osmoregulate in all post-embryonic stages of land-locked, FW-inhabiting shrimps from the Pantanal is most striking.