What They Did Back Then

* Master of Science in Aquaculture completed 1998, University of Guelph

Advisor: Professor Richard D. Moccia

Systemic absorption of oxytetracycline administered by short-exposure bath to Rainbow Trout, Onchorhynchus mykiss.


Since bath administration of chemotherapeutants has numerous benefits over oral and injection methods, an extension of its traditional use for topical diseases, to one that would treat systemic diseases is favoured. The present investigation focuses on establishing levels of a systemic absorption of a popular aquaculture antibiotic, oxytetracycline, when administered in a one- hour bath at 400mg/l, 500mg/l, 600mg/l, and a two hour 600mg/l bath to Rainbow Trout. Serum residues of this antibiotic present during and after exposure are determined using a microbiological plate assay. The detected levels of OTC in the serum were highly variable within each exposure trial and within each exposure time. Generally, serum concentrations increased with bath concentration was calculated to be > 1000 ppb, and occurred in the 600mg/l two-hour bath. Serum concentration levels below 125 were most prevalent in the 400 mg/l bath. In all trials, serum levels reached a peak and began to decline within the five-hour observation period. Variable results are attributed to individual differences in susceptibility to chemical uptake as a result of genetic, behavioral, and/or health status variation, as well as the assay sensitivity. Serum levels detected are not comparable to minimum inhibitory concentrations of oxytetracycline for most common bacterial fish pathogens.