Use of a thiamine antagonist to induce Cayuga-Syndrome-like mortalities inlarval Atlantic salmon

A thiamine deficiency has been associated with the development of naturally occurring thiamine-responsive mortality syndromes in Atlantic salmon Salmo salar from the Finger Lakes of New York (Cayuga syndrome) and the Baltic S ea (M74). There is, however, a large range in symptomology and mortality bo th within and between the individual syndromes, leading to uncertainty as t o the exact role of thiamine. We evaluated the dose-response relationship o f oxy thiamine, a thiamine antagonist, administered to sac fry of an Atlant ic salmon with thiamine levels slightly above the reported threshold for de velopment of Cayuga syndrome. We compared the effects of oxythiamine with t hose of the naturally occurring mortality syndromes. Oxythiamine produced d ose-dependent increases in mortality (LD50 = 4.39 nmol/g) and clinical sign s that were similar to those reported for Cayuga syndrome and M74. increasi ng oxythiamine resulted in dose-dependent increases in lethargy, generalize d and branchial vascular pallor, yolk sac opacities, yolk sac edema, hemorr haging, vascular congestion, exophthalmia, and hydrocephalus that preceded mortality. These data provide experimental evidence supporting the hypothes is that a thiamine deficiency in the natural environment is the cause of Ca yuga syndrome.