Nitrogenous waste excretion in resting dogfish occurred largely (>90 %) as urea-nitrogen (urea-N) efflux across the gills, with a very small urea efflux via the kidney. Ammonia excretion, almost entirely at the gills, accounted for less than 3 % of total nitrogen excretion. Given the extremely high blood urea levels (approximately 640 mmol-N l-1) 'retained' for osmoregulation, and blood ammonia levels (approximately 80 µmol-N l-1) comparable to those of teleosts, the gills of resting dogfish were exceptionally impermeable to both urea and ammonia. Experiments investigated the origins of these low permeabilities and the responses of urea-N and ammonia-N excretion and acid­base status to 6 h infusions with iso-osmotic solutions of NaCl (control), NH4Cl, NaHCO3, urea and its analogues thiourea and acetamide. NaCl had no effects, whereas NH4Cl loading caused intense acidosis and marked elevation of acidic equivalent, ammonia-N and urea-N excretion rates, the latter despite unchanged blood levels of urea-N. Apparent branchial ammonia permeability increased greatly. Acidosis resulted from both stimulated urea production and branchial NH3 loss, the former making the larger contribution. NaHCO3 loading caused intense alkalosis, a marked elevation of basic equivalent excretion and a moderate stimulation of urea-N excretion. Blood urea-N levels were again unchanged. Infusion of urea itself raised blood urea-N levels, but initially reduced branchial urea-N excretion. Acetamide and thiourea infusions both moderately elevated branchial urea-N excretion. We suggest that the low ammonia permeability may arise metabolically from an ammonia scavenging system in the gills, that a 'back-transport' mechanism in the gills may contribute to the low urea permeability, and that the dissociation between blood urea-N levels and excretion rates may reflect urea production at extrahepatic sites. These studies demonstrate that urea synthesis in the dogfish is linked more to nitrogen availability than to acid­base status.
In the field: an interview with Harald Wolf
(update)-Conversation.jpg?versionId=3747)
In our new Conversation, Harald Wolf talks about his fieldwork experiences working with desert ants in Tunisia to understand their navigation.
Propose a new Workshop
-GSWorkshop.png?versionId=3747)
Our Workshops bring together leading experts and early-career researchers from a range of scientific backgrounds. Applications are now open to propose Workshops for 2024, one of which will be held in a Global South country.
Julian Dow steps down and John Terblanche joins the JEB team
-NewEditor.png?versionId=3747)
After 15 years with the journal, Julian Dow from University of Glasgow, UK, is stepping down as a Monitoring Editor. We wish Julian all the best for the future and welcome John Terblanche, Stellenbosch University, South Africa, who is joining the team. Julian talks about his long association with The Company of Biologists and the journal and John tells us about his life and career in this News article.
The capture of crude oil droplets by filter feeders at high and low Reynolds numbers
-FilterFeeders.jpg?versionId=3747)
Researchers from the University of Montreal, Canada, reveal how tiny filter feeding barnacles and Daphnia entrap and consume minute droplets of crude oil, introducing the pollutant at the bottom of the food chain.
Patterns and processes in amphibious fish
-Review.png?versionId=3747)
In their Review, Keegan Lutek, Cassandra Donatelli and Emily Standen discuss the biomechanics and neural control of terrestrial locomotion in amphibious fish. They explore how locomotor mode depends on body shape, physical constraints and phylogeny.
Social media
