Pulsatile urea excretion in the ureagenic toadfish Opsanus beta: an analysis of rates and routes

摘要: This study focused on the rates and routes of urea-N ammonia-N excretion in ureagenic toadfish possibility that occurs pulses. Experimental approaches included following: confinement small individual containers with automated hourly sampling water to follow temporal patterns; divided chambers separate from anterior posterior parts fish; collection urine rectal fluid via chronic indwelling catheters; gavage [14C]-labelled polyethylene glycol 4000 detect regurgitation gastrointestinal fluids. When a standardized 'crowding' pre-treatment was employed induce ureotelic behaviour, fish exhibited significant elevations activity glutamine synthetase liver, kidney gills, elevated plasma bile levels, but unchanged levels most other body Unencumbered confined excreted 82 % their waste-N as 18 ammonia-N; almost all (94 %) this occurred single pulse less than 3 h duration about once every 24 h. daily did not occur by gut fluids, through prominent pores behind pectoral fins or discharge urine. Intestinal urinary accounted for 10 whole-body negligible fraction excretion. Pulsatile at head end across gills and/or surface. Ammonia-N excretion, which pulsatile, also largely end. However, had been placed chambers, became continuous rather increased greatly. A severe stress response indicated high cortisol, skin, lacks scales, route both We speculate normal adaptive significance is ureotelism facilitates cryptic allowing virtually eliminate N-waste during long periods while it remains sheltered burrows. stress, effects extremely cortisol overwhelm ammonia urea retention mechanisms, substances leak general