Ionic aspects of the physiology and biology of Macrobrachium rosenbergii (De Man) 1879.
The giant Malaysian freshwater prawn, Macrobrachium rosenbergii spends
its juvenile and adult life primarily in freshwater. The larval stages of this species
require brackishwater for their survival and development. Adult females of
Macrobrachium rosenbergii migrate into brackishwater to spawn, and some populations
of this prawn live entirely in brackishwater. Other Macrobrachium species have larval
stages that require brackishwater for development. Some Macrobrachium species do not
require brackishwater for larval survival and have abbreviated larval development.
The ,ionic requirements for successful larval development and
metamorphosis were studied using a formulated artificial seawater. It was found that trace
element impurities, either in the salts used in the artificial seawater, or contained within
the artemia fed to the larvae, were sufficient to allow normal larval development. The
omission of bromide from the artificial seawater was found to cause total mortality to
early stage larvae. Further work attempted to discover the minimum threshold
concentration of bromide required by the larvae.
The manner by which Macrobrachium rosenbergii adults regulate the ionic
composition of their haemolymph when exposed to freshwater and brackishwater of
varying salinity was investigated. The effect of the moult cycle on divalent cation
regulation is studied. It was found that in varying salinity adult Macrobrachium showed a
strong regulation of its haemolymph osmotic pressure, Na, Cl, Mg, Ca, K and Sr
concentrations. The haemolymph Ca and Br concentration increased with increasing
salinity, while the haernolymph Cu concentration decreased. The high concentration of
bromide and strontium in the haemolymph of prawns held in freshwater was regarded as
an indication that they might be essential to the adult prawn. The implication of their roles
was in the process of cuticle hardening. A close relationship between haemolymph
strontium and magnesium concentrations was revealed, although the significance of this is
The effect of the moult cycle on haemolymph divalent cation regulation
revealed that Ca and Cu decreased after the ecdysis. Haemolymph magnesium
concentrations were elevated during pre- and postmoult. Strontium increased markedly
prior to ecdysis, this was further evidence as to a potential role in the calcification process. The haemolymph bromide concentration was reduced during pre- and postmoult.
This was attributed to, either its incorporation into the cuticle, or increased ionic fluxes
during the pre- and postmoult period.
The calcification of the larval stages of Macrobrachium rosenbergii was
investigated. The larvae are calcified in a similar manner to the postlarvae. Concentrations
of strontium and bromine in the postlarvae decrease when they are transferred to
freshwater. Analysis of larval exuviae revealed high concentrations of bromine
(=1000ppm) confirming its role in the sclerotisation of the larval cuticle. A close
relationship was found between the strontium and magnesium concentrations of the larvae
and postlarvae held in seawater, confirming this discovery in the adult haemolymph. Such
a relationship was not found between these ions and calcium.
Salinity did not affect the function of Macrobrachium rosenbergii
haemocyanin significantly. This was attributed to the relatively stable internal ionic
environment that this prawn is able to maintain over a wide range of salinities.
Temperature had a pronounced effect on the haemocyanin oxygen affinity. The oxygen
transporting characteristics of Macrobrachium rosenbergii haemocyanin were similar to
those found for marine and brackish water crustaceans. The P02 of Macrobrachium
rosenbergii haemolymph was found to be substantially lower than the P02's recorded for
marine and brackish water species. This was attributed to a reduced perfusion of the gills
by haemolymph. The reason for this was supposed to be a means by which this prawn
reduces its permeability, and hence loss of ions, when in freshwater.