Polymerase Chain Reaction Amplification of Genetic Loci from Diseased Channel Catfish Found Dead in Ponds

Abstract

Abstract As part of a selective breeding program for farm-raised channel catfish Ictalurus punctatus, we screened diseased fish to identify genetic markers linked to disease resistance or susceptibility. Because many diseased fish in ponds are not detected until after death, we investigated the utility of DNA isolated from diseased channel catfish found dead in ponds. Channel catfish (4–25 g) diagnosed with enteric septicemia of catfish or saprolegniasis were sampled 24–48 h postmortem from infected ponds. Control fish were killed by anesthetic overdose and sampled immediately. Total DNA isolated from liver, muscle (with skin), and caudal fin was quantified and analyzed for degradation. Yield of purified DNA, measured as micrograms of DNA per milligram of tissue, was significantly (P < 0.05) lower in diseased fish than in controls. Two sets of DNA primers were used to amplify a portion of the channel catfish growth hormone gene and the mitochondrial D-loop region with the polymerase chain reaction. Degrad...