Book Description

Osmoregulation and endocrine control of osmoregulation were studied in the euryhaline stingray, Dasyatis sabina. In hypersaline sea water (above 35ppt), the ability to regulate plasma solutes was reduced relative to regulation in the optimum, hyposaline (12-28ppt) range. Survival in high salinities was dependent on slow acclimation, while rapid change to low salinities was tolerated. These results appear consistent with adaptations necessary for salinity changes occurring in a bay environment. Natural, uninduced rectal gland secretion was obtained in D. sabina. The average chloride concentration of the rectal gland fluid was 583.3 m-moles/1. The average flow rate was 0.13 ml/kg/hr. Occurrence and amount of rectal gland secretion were erratic. Thyroidectomy, in sea water of 23ppt salinity, caused a significant rise in plasma urea concentrations in D. sabina. Replacement injections of thyroxine lowered plasma urea levels in thyroidectomized animals. Removal of the rostal pars distalis caused plasma urea to increase. Replacement injections of prolactin lowered plasma urea levels, as did replacement ACTH injections. Replacement of both prolactin and ACTH caused variable results concerning urea. Problems of dosage, stress, and possible seasonal influences, most likely affected the results of the endocrine study