Antibiotic name and dosing period(s)
Oxytetracycline (OTC) 100% Active. Two 10-day treatments under 2 Medication Authorities, with the first treatment starting 21 January until 30 January 2026, and the second treatment starting 31 January until 9 February 2026.
Summary of sampling undertaken
The Monitoring Schedule required that water, sediment and wild fish samples were collected during treatment and post-treatment (day 1 post-treatment, and every 7 days thereafter post-treatment until 2 consecutive results are below limit of reporting).
From 20 March the requirement for water, sediment and fish sampling to be undertaken on the same day was changed to samples being taken in the same week, to allow flexibility to meet safety and weather requirements for electrofishing.
Samples were collected at sites both inside the hatchery and within the River Derwent.
In total, 72 individual wild fish samples were caught downstream of the hatchery and analysed. The 72 wild fish samples included 5 species, with short-finned eels (Anguilla australis), being the most commonly captured species.
At the time of reporting, 68 sediment samples and 44 water samples had been collected and analysed at multiple locations within the hatchery and within the River Derwent.
Sediment sampling is continuing at 2 locations until residues of OTC fall below the limit of reporting for two consecutive samples.
Assessment of compliance against the schedule issued by the EPA
The report is compliant with the requirements of the
Therapeutant Residue Monitoring Schedule Meadowbank Hatchery January 2026, and any minor variations approved by the EPA Director.
A minor non-compliance has been identified and acknowledged, with a mid-treatment sediment sample not being collected in the correct location. Water sampling and fish sampling was undertaken as required.
Summary of findings in report
A total of 12 water samples collected from 3 sites showed OTC residues above the limit of reporting during treatment and for 3 weeks post-treatment. All sites were below the limit of reporting by week 4, and water sampling concluded on 24 March 2026 (week 6).
Only 3 fish samples (all short-finned eels) showed OTC residues above the limit of reporting during the first 3 weeks post-treatment. No fish samples reported any OTC traces after week 3, and fish sampling concluded 5 weeks after treatment finished.
Sediment samples contained OTC residues from mid-treatment onwards at 5 locations, with upstream of the hatchery being the only site at which OTC was not detected. The highest concentrations were detected in the sludge tank.
A final report is required to be submitted 4 weeks after the final sampling round.
Statement from the Director of Public Health
Public Health Services notes the report of monitoring for oxytetracycline (OTC) residue in wild fish, sediment, and water, related to treatment of hatchery stock with a total of 51.7 kg of OTC, from 21 January to 9 February 2026.
Seventy-two fish samples were collected between 1 and 35 days after the end of treatment. Residue of OTC was detected in one short-finned eel sampled 7 days after the end of treatment, and 2 short-finned eels sampled 21 days after the end of treatment. The concentrations of OTC detected were 0.02 mg/kg (2 eels) and 0.05 mg/kg (one eel). Eating typical amounts of these wild finfish does not pose a risk to human health. OTC was not detected above the limit of reporting in any of the remaining 69 fish.
OTC was detected in water at the point of discharge to the River Derwent from 1 to 21 days after the end of treatment, in steadily decreasing concentrations. OTC was detected in water near the point of discharge and 500 m downstream during treatment, and near the point of discharge 1 and 7 days after the end of treatment, but not thereafter. None of the concentrations of OTC detected in River Derwent water more than a week after the end of treatment exceeded 1 microgram (ug) per litre (1 part per billion). OTC was not detected in River Derwent water samples collected far downstream of the hatchery either during treatment or in the following 6 weeks.
These monitoring results indicated that the use of OTC in January and February 2026 did not pose a risk to human health through plausible exposure routes.
Link to interim report:
Interim Report - Therapeutant Residue Monitoring Program - Meadowbank Hatchery (PDF 1Mb)