Remediation of Cayuga Syndrome in Landlocked Atlantic Salmon Salmo salar Using Egg and Sac‐Fry Bath Treatments of Thiamine‐Hydrochloride

A lethal thiamine deficiency, termed Cayuga Syndrome (CS), affects larval landlocked Atlantic salmon Salmo salar in several of New York's Finger Lakes. This syndrome has been linked to a maternal diet of alewife Alosa pseudoharengus that have high thiaminase concentrations within them and were not endemic to the Finger Lakes. We evaluated thiamine bath treatments at a range of concentrations for remediation of the syndrome (CS) by treating eggs during water‐hardening or sac‐fry at the onset of CS when clinical signs such as yolk sac and cerebral edema, vascular and mandibular abnormalities, and in particular when abnormal swimming, lethargy and yolk sac oppacities, first became evident. Concentrations of thiamine in sac‐fry from both treatments were elevated by a single 1‐h exposure of eggs or sac‐fry in a thaimine bath. Thiamine concentrations of at least 1,000 mg/L. during water hardening, or 10,000 mg/L if treated as moribund sac‐ky, were necessary to almost eliminate syndrome‐related mortality. When post‐treatment total thiamine tissue concentrations (i.e., the sum of thiamine pyrophosphate, thiamine mono‐phosphate and free thiamine) approached or exceeded a threshold of 0.8 nmol/g sac‐fry in the sac‐fry, mortality due to CS was significantly reduced. Earlier treatment at the egg hardening stage may provide a greater likelihood of avoiding long term effects of the deficiency.