California Sea Grant College Program

Withering syndrome (WS) is a catastrophic disease of both wild and cultured abalone caused by “Candidatus Xenohaliotis californiensis”, a Rickettsia-like procaryote (WS-RLP). Losses from this disease have severely hampered the abalone aquaculture industry and abalone restoration efforts in California. Oxytetracycline (OTC) was recently demonstrated to be an effective therapeutant for WS-RLP infections and associated losses due to WS. In addition, a long duration of protection (approximately one year) was noted anecdotally. Part one of this study examined the efficacy and pharmacokinetics of OTC treatment in red abalone, Haliotis rufescens, held at 13.4oC. Medication was administered orally in an artificial diet containing 1.85% active OTC at a rate of 103.4 mg/kg abalone for 10, 20 and 30 days. Control abalone were fed the same diet lacking OTC. Significant differences in prevalence and intensity of infection in both the post-esophagus and digestive gland were observed. Although the digestive gland from abalone medicated for 10 days and foot muscle from those medicated for 30 days was best described with a two-compartment model, pharmacokinetic trends were adequately described by a one-compartment model. Significant differences in OTC accumulation and depletion were observed among treatments. Animals medicated for 10 days accumulated significantly less than those medicated for 20 or 30 days. Despite this, terminal elimination rate constants were similar. Significantly less OTC was present in foot muscle samples relative to corresponding digestive gland samples. Estimated half-life values were similar among treatments for both foot muscle (10.7-13.4 d) and digestive gland (23.8-27.5 d) samples.