Rotenone treatment of Campvale Drain
Rotenone treatment of Campvale drain, Medowie to eradicate platyfish, Xiphophorus variatus: A post-eradication report, July 2009
Introduction
A new non-native species, known as the platyfish or variable platyfish (Xiphophorus variatus) was confirmed by NSW Department of Primary Industries (NSW DPI) in Campvale drain Medowie, NSW in February 2008. Platyfish are native to Mexico and Central America and is related to Gambusia holbrooki (Gambusia) and swordtails. Platyfish are a popular tropical aquarium fish in Australia and are currently on the national List of permitted live freshwater fish suitable for import, administered by the Commonwealth (Department of Agriculture and Water Resources).
The Campvale drain is an artificial drainage channel which leads into Grahamstown Dam (part of the Williams River catchment), the Hunter region’s largest drinking water supply dam. It is not known how platyfish were introduced into the drain however the most likely vectors are deliberate release from an aquarium or escaped from a backyard pond during flood events.
A comprehensive survey program was undertaken during August 2008 to determine the distribution and abundance of the species, and identify the options for control. A total of 12 sites were identified for sampling, chosen based on the suitability of the habitat to platyfish. Platyfish were only found at two of the 12 sites, and a total of 40 platyfish were caught over four separate sampling events. The two sites were approximately 600 metres apart, in a stretch of the drainage channel adjacent to Ferodale Park Sports Ground and the Medowie Village shops.
The NSW DPI Aquatic Biosecurity Unit prepared a Review of Environmental Factors to use rotenone to control platyfish in Campvale drain at Medowie. Eradication was attempted in January 2009 under permits granted by the Australian Pesticides and Veterinary Medicined Authority (APVMA), Permit 9117. Assistance, including resources and experience, was contributed by Port Stephens Council (PSC). Hunter Water was also consulted and supported the eradication attempt.
Rotenone was identified as the most effective method available for eradicating the known population of platyfish from Campvale drain. The use of rotenone to eradicate pest fish is strictly managed under a permit granted by the APVMA. Rotenone is a chemical used to kill pest fish but it can also affect insects, spiders and mites. Rotenone is made from the roots of plants belonging to the genus Derris. Rotenone is a selective, non-specific insecticide commonly sold as “Derris Dust” and is used in home gardens for insect control and for lice and tick control on pets. It is used worldwide for pest fish eradication due to its relatively low toxicity to non-target species, and its ability to quickly biodegrade. Rotenone is quickly absorbed by the gills of fish and inhibits cellular respiration.
One of the many advantages of using rotenone to eradicate pest fish is that it can be rapidly and completely neutralised (detoxified) by solutions of potassium permanganate. Potassium permanganate is a very effective detoxicant and accelerates the natural breakdown of rotenone within the water. It is a strong oxidising agent that does not generate toxic by-products.
Prior to the eradication attempt a comprehensive fish survey of the drain was conducted by electrofishing and trapping. Fish present included two species of native gudgeon (one each of: flathead gudgeon Philypnodon grandiceps and fire tail gudgeon Hypseleotris galii), large numbers of the non-native and noxious fish Gambusia holbrooki (Eastern gambusia), approximately 30 platyfish and a large number of Cherax destructor (a translocated population of yabbies native to NSW western drainages). The native species were removed and relocated upstream of the treatment site.
Materials and methods
The volume of water in the drain was carefully calculated in order to correctly apply the required dose of rotenone to each section of the drain. The total volume was estimated to be 1000m3. In addition the water level in the drain was lowered to reduce the amount of rotenone required and to eliminate refuges for pest fish in macrophytes. The drain is divided into two discrete sections by the Ferodale Road Bridge (Figure 1) which has a concrete sill underneath it. The water was lowered in the upstream section (Section 1; Kirrang Drive Bridge to Ferodale Road Bridge) by pumping water under the bridge into the downstream section (Section 2).
Port Stephens Council (PSC) staff set up a number of advisory signs to warn members of the local community of the operation and adjacent local residents were advised by letterbox drop three days prior to the commencement of works. A temporary clay bund (Figure 2) was installed in the drain by PSC staff at the downstream end of Section 2, which is the limit of PSC land, and allowed for the drain level in this section to be lowered.
Once the water level in Section 2 of the drain had been lowered, rotenone was applied at a dosage rate of 3mg per litre of active rotenone. The rotenone was mixed with water in a 1000 litre tank installed on the tray of a 4 wheel drive vehicle (Figure 3).
NSW DPI officers drove the vehicle alongside the drain while the spray operator dosed the drain. At the conclusion of the rotenone treatment the drain levels remained lowered. The following day, the drain was dosed with potassium permanganate to ensure the rotenone was neutralised (using the same spray equipment). NSW DPI staff involved in the operation wore appropriate personal protective equipment during mixing and application of rotenone and potassium permanganate. On the two days following treatment NSW DPI staff collected dead pest fish from the drain and disposed of them by burial on site.
Results
Large numbers of Eastern gambusia and small numbers of platyfish were observed during the rotenone treatment on 20 January 2009 and several hundred dead Eastern gambusia as well as 90 platyfish were removed the following day and buried. No native fish were observed floating in the drain or on the bank following treatment. Eastern gambusia were observed swimming in the last 30 metres of the treated section on the two days following rotenone treatment and neutralisation. Live yabbies and water beetles were observed throughout the entire treated section of the drain on days following treatment.
NSW DPI staff have since conducted follow up surveys of the area to assess the success of the eradication attempt. These surveys were conducted in March 2009, and July 2009.
The March 2009 survey results found juvenile and adult platyfish in both sections of the drain. The results were inconclusive however as to whether the eradication attempt was unsuccessful, or whether the drain had been restocked from another source of the fish.
A second survey was conducted in July 2009, to assess whether platyfish were present in dams on private land adjacent to the drain, as this could be a potential source of the pest fish. Fortunately, all landholders of the target properties gave permission for fish surveys to be undertaken on their property. Five ponds were surveyed (by electrofishing) and platyfish were discovered in one large dam (in small numbers).
Discussion
As with all pest fish, once the population is widely distributed, it is difficult, if not impossible to eradicate them. Unfortunately, as the eradication was not successful, and surveys have shown that the fish are widely distributed throughout the drain, and in at least one private dam, the eradication of the platy is no longer considered viable.
With any pest fish eradication attempt there is always a chance that they may re-occur. This could be through the release of unwanted pet platyfish from a home aquarium, flooding resulting in release from outdoor ponds, or that the eradication attempt was unsuccessful.
Acknowledgements
Port Stephens Council donated considerable in-kind support to the eradication attempt including several staff, machinery, equipment and signage with an approximate value of $10,000. Their expertise and assistance were greatly appreciated and ensured the attempt was conducted with minimal difficulties.
NSW DPI research staff conducted fish surveys to establish the scope of the platyfish population and to assess the number of native species.