Risk analysis of the Amur sleeper Perccottus glenii: risk analysis report of non-native organisms in Belgium - update

Executive summary
PROBABILITY OF ESTABLISHMENT AND SPREAD (EXPOSURE)
Entry in Belgium It is very likely that Amur sleeper will enter Belgian waters in the near future if it were to be used as an aquarium fish. Especially fish transports from fish farms in infested areas (where Amur sleeper can be present as a stowaway) to local fish farms here may serve as an important entry pathway. From aquaculture ponds it may spread via escapes or through fish stocking activities.
Establishment capacity Perccottus glenii is not yet present in Belgium or neighbouring, interconnected river systems. However, all literature indicates a high probability of future establishment in most parts of Belgium (especially Flanders with its standing and slow streaming waters).
Dispersion capacity Human aided dispersal (aquarium trade and aquaculture) has helped Amur sleeper to invade large parts of Eurasia. Natural spread was probably the main vector for downstream dispersal. Because of high propagule pressure from high density populations in standing waters in flood plains, the importance of this last vector must not be underestimated in the widespread distribution of P. glenii.
EFFECT OF ESTABLISHMENT
Environmental impacts The environmental impacts of the presence of Amur sleeper in Belgium will be through competition for food and predation but also possibly through pathogen pollution and disruption of trophic interactions. Mainly native freshwater fish and amphibians will be affected but also (larvae of) large invertebrates will be heavily predated upon. Especially standing waters (oxbow lakes, ponds, etc.), where high densities of P. glenii can be expected, will be the ecosystems at risk.
Other impacts In aquaculture facilities and in commercial fishing grounds, Amur sleeper may be a competitor for food and may thus reduce production of economically important fish species. Social impacts, however, have not been reported.
CONCLUSION FOR RISK ASSESSMENT
The Amur sleeper may easily reach Belgium as a stowaway of fish consignments and/or escapes or releases from aquaria. Once introduced, its establishment capacity is considered very high in standing or slow running waters. It represents a moderate to high risk for native biodiversity (e.g. amphibians). Recent records of this species in open waters in the Upper Danube basin close to the mouth of Main-Danube Canal may be a start of active migration of Amur sleeper or passive dispersal with ships into the canal towards rivers in Western Europe.
COCLUSION FOR RISK MANAGEMENT
Amur sleeper is not easy to detect or observe at early stages of invasion and rapid eradication is therefore difficult. Piscicides and ammonia may be useful in eradicating emerging Amur sleeper populations but only in (small) confined areas and at a big cost. A reduction of population density may be achieved by piscivorous fish species like pike and perch. Prohibition of the trade and use as aquarium fish or live bait of Amur sleeper can reduce the risk of species introduction in Belgium. Although it may be quite difficult to implement, import control of large trucks for fish transport and surveillance of fish stocking activities deserve to be done as stowaway specimens of Amur sleeper are regularly reported in fish consignments.