28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Myopathy In Cultured Toadfish Roxanna Smolowitz and Janice Hanley Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543 The toadfish, Opsanus tau, is an important marine animal model used in laboratory research.  In the wild, toadfish do not reach an appropriate research size for approximately several years.  In the last three years, the Marine Resources Center (MRC) at the Marine Biological Laboratory, has studied species specific culture methods for this important fish.  Feeding and water temperature experiments were used to identify methods of increasing the growth rate of juveniles hatched from eggs held in the MRC.  A matrix including three temperatures (23, 26 and 29 oC) and three foods (commercially manufactured trout pellets; harvested, frozen butterfish and purchased frozen shrimp) were used to study growth rate in five-month-old toadfish.  Approximately seven months into the experiment (age 11 months), major fluctuations in the salinity of all tanks in the experiment repeatedly varied between 28 and 50 ppt over a two week period.  During that time, and in the following two weeks, all toadfish, held at all three temperatures and that were fed the butterfish diet, died.  Moribund fish exhibited open mouths, increased respirations, and poor stability in the water column.  Necropsy findings were anasarca, enlarged whitish livers, severe anemia and rarely hydroperitoneum.  Microscopically, multifocal degenerative myopathy with myofiber hyalinization, fragmentation and macrophagic inflammation were noted in skeletonal muscles primarily of the back and jaws.  Secondary filaments of the gills contained large numbers of chloride cells along their entire lengths.  Other findings included edema of connective tissues, hepatic lipidosis and mild multifocal hydropic degeneration of hepatocytes.  Presumptive diagnosis was nutritional myopathy caused by Vitamin E/selenium deficiency resulting from high lipid, possible poorly preserved , fatty fish food diet coupled with severely fluctuating, salinity induced stress.  (Funded by NIH grant DCO1837) Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page