| Abstract |
Atyaephyra desmarestii has a wide distribution in continental waters around
the world. The study of this species is carried out on the level of three Tunisian
reservoirs, Sidi Salem, Lebna and Sidi Saâd dams. Distance among these three
reservoirs, their location on three distinct bioclimatic areas, the absence of hydro-
logical communication between them and their differences in salinity (average
values 1.37, 0.7 and 2.8‰, respectively), as well as morphological and biological
differences appearing among individuals of the three populations, encouraged
us to look for the existence of possible differences in osmotic regulation in
the three populations. The preliminary results obtained did not show significant
differences in the osmotic regulation among the three populations. The recorded
osmotic pressures obtained for individuals maintained during 24 hours in fresh
water mediums at osmotic pressures of 7 mos.kg -1 (Sidi Salem shrimps) and
6 mos.kg -1 (Sidi Saâd and Lebna shrimps) were 330 ± 18.33, 333 ± 20 and
326 ± 27 mos.kg -1 for the populations of each reservoir, respectively. In salt
water (approximately 25‰, obtained by dilution of sea water from Montpellier
by addition of distilled water), the shrimps were maintained for 24 hours in
salted mediums of osmotic pressures of 804 mos.kg -1 (Sidi Salem shrimps), 757
mos.kg -1 (Sidi Saâd shrimps) and 756 mos.kg -1 (Lebna shrimps) the osmotic
pressures recorded for the three populations were respectively 809 ± 8, 761 ±
11 and 760 ± 10 mos/kg. Thus, an intraspecific physiological variation between
these populations did not appear to exist for the mineral-water metabolism and
under the conditions of the experiment. However this study has permitted us
to identify for the first time the hyper-iso-osmotic type of regulation of this
fresh-water crustacean. |
