Exposure to Feedborne Mycotoxins T‐2 Toxin or Ochratoxin A Causes Increased Mortality of Channel Catfish Challenged with Edwardsiella ictaluri

To evaluate the effect of mycotoxins on the disease resistance of juvenile channel catfish Ictalurus punctatus , we conducted an experiment in aquaria under controlled environmental conditions. Catfish were fed a nutritionally complete semipurified diet containing two concentrations of either T‐2 toxin (1.0 or 2.0 mg/kg diet) or ochratoxin A (OA; 2.0 or 4.0 mg/kg diet). Mycotoxins were supplied as pure, crystalline T‐2 toxin diluted to a known concentration in a carrier of casein and Aspergillus ochraceus culture material containing a known concentration of OA. After 6 weeks of feeding, catfish were challenged by immersion in situ with a virulent isolate of Edwardsiella ictaluri suspended in nutrient broth that provided an estimated 2.25 × 10 6 colony forming units per milliliter of water. At 21 d postchallenge, significantly ( P < 0.05) greater mortalities occurred among catfish fed T‐2 toxin, 1.0 or 2.0 mg/kg diet (84.11% and 99.30%, respectively) than among control fish. Fish fed the OA diet (4.0 mg/kg) also had significantly higher mortality (80.49%) than control‐fed catfish, which experienced 68.28% mortality. Results indicate that juvenile channel catfish fed feedborne mycotoxins T‐2 toxin or OA had significantly greater mortality when challenged with E. ictaluri .