Hormones, ionic regulation and kidney function in fishes

Area of Science:

• Comparative physiology
• Endocrinology
• Renal function

Background:

• Fish osmoregulation involves complex hormonal mechanisms.
• Different fish classes (Agnatha, Chondrichthyes, Osteichthyes) exhibit unique renal adaptations.
• Understanding hormonal interplay is crucial for renal homeostasis.

Purpose of the Study:

• To review renal osmoregulatory mechanisms in Agnatha, Chondrichthyes, and Osteichthyes.
• To examine the role of endocrine status and hormonal interplay in renal homeostatic mechanisms.
• To highlight knowledge gaps in the endocrine control of osmoregulation in certain fish groups.

Main Methods:

• Literature review and synthesis of existing research on fish renal physiology and endocrinology.
• Comparative analysis of osmoregulatory strategies across major fish taxa.
• Discussion of hormonal actions and feedback mechanisms in renal regulation.

Main Results:

• Agnatha (hagfishes, lampreys) show atypical osmoregulation with poorly understood endocrine control.
• Chondrichthyes utilize unique hormones like 1-alpha-hydroxycorticosterone for maintaining high urea and trimethylamine oxide levels.
• Teleostei (Osteichthyes) exhibit complex renal mechanisms for euryhalinity, involving the renin-angiotensin system and arginine vasotocin, with evidence of feedback loops.

Conclusions:

• Hormonal regulation of renal function varies significantly across fish lineages.
• Further research is needed to fully elucidate the endocrine control of osmoregulation in Agnatha and Chondrichthyes.
• The interplay between hormones like angiotensin II and arginine vasotocin is critical for osmoregulation in teleosts, especially under varying salinity conditions.