Use of a Thiamine Antagonist to Induce Cayuga-Syndrome-like Mortalities in Larval Atlantic Salmon

Abstract

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 Sea (M74). There is, however, a large range in symptomology and mortality both within and between the individual syndromes, leading to uncertainty as to the exact role of thiamine. We evaluated the dose–response relationship of oxythiamine, a thiamine antagonist, administered to sac fry of an Atlantic salmon with thiamine levels slightly above the reported threshold for development of Cayuga syndrome. We compared the effects of oxythiamine with those of the naturally occurring mortality syndromes. Oxythiamine produced dose-dependent increases in mortality (LD50 = 4.39 nmol/g) and clinical signs that were similar to those reported for Cayuga syndrome and M74. Increasing oxythiamine resulted in dose-dependent increases in lethargy, generalized and branchial vascular pallor, yolk sac opacities, yolk sac edema, hemorrhaging, vascular congestion, exophthalmia, and hydrocephalus that preceded mortality. These data provide experimental evidence supporting the hypothesis that a thiamine deficiency in the natural environment is the cause of Cayuga syndrome.