[Triiodothyronine is needed for the acclimatization of brown trout (Salmo trutta) or rainbow trout (Oncorhynchus mykiss) to seawater].
Brown and rainbow trout, held in freshwater at 13 +/- 1 degrees, were injected, every 3 days, with iopanoic acid (IOP: 5 mg/100 g body wt), an inhibitor of deiodination of thyroxine (T4) to triiodothyronine (T3). One group of IOP-treated rainbow trout was immersed in T3 (20 micrograms/l water). In IOP trout, plasma T3 fell to very low levels by day 7, while changes in T4 levels were less marked. In IOP + T3 trout plasma T3 increased fivefold, plasma T4 being unchanged. No mortality occurred and plasma osmolarity (OP) was not altered by any treatment. After direct transfer to seawater (30/1000), IOP trout were unable to acclimate to salinity: all died within 2 or 3 days, while the survival at day 3 was 100% in control brown trout and 45 and 74% in control and IOP + T3 rainbow trout respectively. OP increased more in IOP and less in IOP + T3 than in controls. There was a significant inverse correlation between T3, but not T4, plasma level, at the time of transfer and the OP 1 day later. In conclusion, although T3 does not play a significant role in osmoregulation in freshwater, T3 and therefore the deiodination of T4 into T3, were required for the development of hypo-osmoregulatory capacity involved in acclimation of trout to seawater.
Lebel
J M
JM
Laboratoire de Physiologie générale et comparée du Muséum, C.N.R.S., Paris.
Leloup
J
J
D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D012623:Seawater; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000502:physiology*; D014337:Trout / Q000378:metabolism / Q000502:physiology*; D014882:Water-Electrolyte Balance
D014284:Triiodothyronine; D013974:Thyroxine
La triiodothyronine est nécessaire à l'acclimatation à l'eau de mer de la truite fario (Salmo trutta) ou arc en ciel (Oncorhynchus mykiss).