Aspects of osmoregulation in the common prawn, Palaemon Serratus (Pennant, 1777)

Teinsongrusmee, Banchong (1976) Aspects of osmoregulation in the common prawn, Palaemon Serratus (Pennant, 1777). University of Southampton, Doctoral Thesis.

Abstract

The common prawn, Palaemon serratus (Pennant) regulates the sodium in its haemolymph hypertonically in a sea water concentration below 70%, whereas in a medium concentration above 70% SW the animal regulates its sodium concentration in the haemolymph hypotonically. In normal sea water, there is an inverse correlation between the haemolymph sodium concentration and temperature. In 50% SW the haemolymph sodium concentration increases irregularly with increased temperature. In 125% SW, within a temperature range of 5° to 15°C, the sodium concentration in the haemolymph of the prawn decreases with increasing temperature, but it increases with increasing temperature when the prawn is exposed to temperatures ranging from 15° to 25°C. Within the range of salinity between 5% to 125% SW, the prawn regulates its water content very efficiently especially in a temperature range from 5° to 25°C. Reverse peristalsis in the hind gut and water drinking by prawns exposed to different osmotic stresses were observed. The animal takes in the water via the mouth and the anus. In normal sea water the drinking rate via both routes, was about 0.69 ± 0.13% body wt/hr. The drinking was continuous and decreased irregularly with decreased salinity varying from about 0.42 ± 0.08% body wt/hr to 0.26 ± 0.07% body wt/hr in 70% and 50% SW respectively. Temperature also affects the drinking rate, a reduction of temperature from 15° to 5°C results in a decrease in the drinking rate by about a half. The haemolymph volume of prawns acclimated to a salinity range of 10% to 100°% SW lies between 19.44 ± 2.26% and 21.52 ± 4.76% body wt. The systems responsible for control of the haemolymph, volume are the antennal glands and the sodium transport mechanisms. The former is responsible for eliminating or retaining water whereas the latter is involved in maintaining the constancy of osmotic and ionic levels of the haemolymph. The bladder volume of prawns averaged about 2.61% body weight though with considerable variability. In 100% SW the prawn produced urine at a rate of 0.44% body wt/hr whilst the rate in 50% SW was 0.93% body wt/hr. In an isotonic medium, 70% SW, urine production rate was 0.34% body wt/hr. The prawn increases its urine flow as the salinity decreases. At a salinity near the lower limit of its tolerance, 10% SW, the animal increases its urine flow to about twice the rate in 50% SW. When temperature is lowered the rate of urine flow decreases, dropping from 0.44% body wt/hr at 15°C to 0.19% body wt/hr at 5°C. The U/H ratios for Cr-51 EDTA of prawns kept in 100%', 70%, 50%, and 10% SW are 2.34, 2.16, 1.77, and 1.22 respectively, indicating maximum reabsorption of fluid is taking place in normal sea water. The rate of water reabsorption from the urinary bladder decreases as the salinity of the medium declines. Under steady state conditions, the osmoregulatory process in 100% SW involved a continuous swallowing of medium with absorption of univalent ions and water from the gut epithelium; the excess ions were then excreted through the gills by active extrusion pumps to give a net uptake of water to balance the passive osmotic loss. The antennal glands serve to excrete divalent ions. A sodium-potassium exchange pump involved in sodium extrusion has been demonstrated in the gills. The pump is located on the external membrane, and the transport system is inhibited when ouabain is placed in thee bathing medium. The inhibitory action of this glycoside can be antagonised by adding excess K+ to the external medium. In dilute sea water, the prawn swallows very little medium, ions are actively taken up through the gills, and the osmotic inflow of water is balanced by the production of large quantities of isotonic urine. The possible hormonal control of salts and water balance in the prawn was studied by bilateral eyestalk ablation experiments. In 100% SW the haemolymph sodium concentration and the rate of urine flow of animals with ligatured eyestalks are similar to that of the controls, but there are significant differences in the rate of water drinking, the haemolymph volume, and the rate of water reabsorption in the bladder. Eyestalk ablation elevates the U/H ratio for Cr-51 EDTA of the prawn from 2.34 to 2.94 which indicates a higher rate of water reabsorption from the bladder than the normal prawn, suggesting that the water reabsorption from the urinary bladder may be controlled by an eyestalk factor. When prawns are subjected to a sudden change from 100% to 50% SW the haemolymph sodium concentration of animals with ligatured eyestalks and normal animals, reached a new steady state within 6 hours after the transfer whilst animals with their eyestalk ligatured maintained a sodium steady state higher than the normal animals. In 50% SW, eyestalk ablation caused no change in urine flow or haemolymph volume, but it raises the concentration of sodium in the haemolymph, and also the rate of sodium efflux. By using a basic dye, thionine, evidence is produced which suggested the possibility that the sodium pump at the gills is controlled by eyestalk factors.

This record has no associated files available for download.

Contributors

Download statistics