Distribution and persistence of the anti sea-lice drug teflubenzuron in wild fauna and sediments around a salmon farm, following a standard treatment.

The salmon louse (Lepeoptheirus salmonis) is a challenge in the farming of Atlantic salmon (Salmo salar). To treat an infestation, different insecticides are used like the orally administered chitin synthetase inhibitor teflubenzuron. The concentrations and distribution of teflubenzuron were measured in water, organic particles, marine sediment and biota caught in the vicinity of a fish farm following a standard medication. Low concentrations were found in water samples whereas the organic waste from the farm, collected by sediment traps had concentrations higher than the medicated feed. Most of the organic waste was distributed to the bottom close to the farm but organic particles containing teflubenzuron were collected 1100 m from the farm. The sediment under the farm consisted of 5 to 10% organic material and therefore the concentration of teflubenzuron was much lower than in the organic waste. Teflubenzuron was persistent in the sediment with a stipulated halflife of 170 days. Sediment consuming polychaetes had high but decreasing concentrations of teflubenzuron throughout the experimental period, reflecting the decrease of teflubenzuron in the sediment. During medication most wild fauna contained teflubenzuron residues and where polychaetes and saith had highest concentrations. Eight months later only polychaetes and some crustaceans contained drug residues. What dosages that induce mortality in various crustaceans following short or long-term exposure is not known but the results indicate that the concentrations in defined individuals of king crab, shrimp, squat lobster and Norway lobster were high enough shortly after medication to induce mortality if moulting was imminent. Considering food safety, saith and the brown meat of crustaceans contained at first sampling concentrations of teflubenzuron higher than the MRL-value set for Atlantic salmon. The concentrations were, however, moderate and the amount of saith fillet or brown meat of crustaceans to be consumed in order to exceed ADI is relatively large.

Mortality and deformities in European lobster (Homarus gammarus) juveniles exposed to the anti-parasitic drug teflubenzuron.

This study describes experiments carried out to examine effects of the antiparasitic drug teflubenzuron, used in delousing farmed salmon, on a non-target species, the European lobster (Homarus gammarus). Juvenile lobsters were fed two doses of teflubenzuron, 10 and 20mg/kg successively for 7 days corresponding to a standard medication of the fish (10mg/kg day) and twice the standard dose (20mg/kg day). Monitoring lasted 3 months to include at least one moulting period for all individuals. Cumulative mortality was higher in all replicates given medicated feed compared with the control group. Mean cumulative mortality for each dosing was 41 ± 13% for 10mg/kg and 38 ± 8% for 20mg/kg, i.e. no difference. Drug residue was analysed in all juveniles that died, in addition to 12 juveniles at day 8 and the first 12 surviving lobsters. A decline in concentration of teflubenzuron from over 8,000 ng/g (day 5) to 14 ng/g (day 70) was observed in the juveniles that died during the experiment. Twelve individuals that died contained 82 ng/g or less whereas the mean concentration in the first 12 lobsters that survived moulting was 152 ng/g. Following a single oral administration, the half-life of teflubenzuron in lobster was estimated to 3.4 days and the initial concentration (C0) to 515 ng/g at time t0. At the end of the study a considerable number of juvenile lobsters were observed with deformities in various organs; carapace, walking legs, cheliped, tail fan, abdomen and antenna. The occurrence of observed deformities varied from 0 to 15% in treated replicates and will most likely affect ability to locate and consume food (antenna, claw and walking legs), respiration (carapace) and ability to move/swim (walking legs, tail fan and abdomen). In total, the mortality and senescent damages were close to 50% in all replicates. Juveniles that survived medication without deformities however, moulted and increased in size at each moult equally well as the unmedicated controls.