STRESS-INDUCED FAILURE OF OSMOREGULATION IN THE PARASITIC NEMATODE PSEUDOTERRANOVA-DECIPIENS - INDIRECT EVIDENCE FOR HORMONAL-REGULATION

When third-stage larvae of Pseudoterranova decipiens maintained at 5-d egrees-C are placed in either 40% artificial sea water (ASW, iso-osmot ic) or 15% ASW (hypo-osmotic) and weighed once at 0 h and again at 24 h, they neither lose nor gain weight, and the osmotic pressure (OP) of their pseudocoelomic fluid (PCF) remains unchanged. In contrast, when worms are weighed six additional times during the 24 h interval, thos e maintained in isoosmotic conditions lose weight, while those maintai ned in hypo-osmotic conditions gain weight. Worms which had been expos ed to hypo-osmotic conditions and weighed at various times between 0 a nd 24 h exhibited an increase in weight which was correlated with the number of weighings. Worms exposed to hypo-osmotic conditions and weig hed three additional times between 0 and 24 h also gained weight, and the OP of the PCF decreased such that worms experiencing the greatest increase in weight suffered the greatest dilution of the PCF. In worms ligatured at the head or tail or at the head and tail, and then expos ed to either 15% or 40% ASW, the effect of multiple weighings is exagg erated in a complex way. The presence of a ligature on the tail in wor ms immersed in an iso-osmotic medium leads to an increase in weight an d to a very marked additional increase in weight in worms immersed in a hypo-osmotic medium. The presence of a head ligature in worms in an iso-osmotic medium leads to a decrease in weight and to a smaller weig ht gain in a hypo-osmotic medium. The addition of a head ligature to w orms ligatured at the tail increases the weight gain in both iso-osmot ic and hypo-osmotic media. These results demonstrate that stress induc ed by handling disrupts the normal capacity to osmoregulate in P. deci piens; they are consistent with the stress-induced release of postulat ed diuretic and antidiuretic factors.