Effect of Storage on Residue Levels of Enrofloxacin in Muscle of Rainbow Trout (Oncorhynchus mykiss) and Common Carp (Cyprinus carpio)

Since fluoroquinolones are one of the most commonly used antibacterial drugs in aquaculture, there is a risk of their residues to be found in the treated fish. The objective of this study was to examine the changes in enrofloxacin and ciprofloxacin levels during storage of rainbow trout and common carp muscle at −18 °C. The trout and carp were treated orally with a single dose of 10 mg/kg of enrofloxacin. Tissue samples were collected 24 h after the treatment and stored at −18 °C for 270 days either as a whole fish or as precut muscle samples. Results for trout revealed that in the precut samples enrofloxacin concentration decreased significantly only after 9 months of storage, whereas a significant decline in the ciprofloxacin level was observed much earlier (after 3 months). After 9 months of storage, the trout stored without being sliced and eviscerated showed significantly higher levels of both quinolones as compared to the precut muscle samples. The enrofloxacin levels in the carp musculature decreased considerably after 3 months of storage and stayed almost unchanged up to the end of the study, whereas the ciprofloxacin concentration continued to drop even after this period and after 270 days constituted 1/6 of the initial values.