Escapes and Introductions — Seafish


Psetta maxima

Escapes and Introductions

Escapees from aquaculture facilities can potentially impact on habitats and species in the receiving water bodies. Problems could occur due to competition, potential disease transfer, establishment of non-native species, interbreeding with wild populations, and impacts on sensitive habitats1, 2, 3.

The potential of fish escaping the farming enclosures is usually higher in ‘open’ culture systems, such as net-pen farms. However, turbot farming in bottom net-pens is rarely used today. The use of on-shore systems (RAS and PAS) significantly limits the potential for escapees. However even though unlikely, escapement is still possible through outlets in flow-through systems e.g. due to accidental release of fertilised eggs, larvae or market-size fish during handling and sorting in proximity to outlets2.

However, research indicates that turbot escapees in Europe are scarce and most individuals of farmed ancestry encountered in the wild originate from re-stocking efforts, rather than commercial aquaculture4.

To reduce escape risks farms should have trapping devices such as screens and grills on all water inlets, outlets and drainage channels that are suitably sized to match the size of the stock. These screens should be regularly inspected, maintained and such actions recorded. Rearing facilities should be of adequate height and standard, able to retain stocks during periods of flood and regularly inspected and maintained. There should be no intentional release of stock from the farm.

The contribution of non-native species to the growth of the global aquaculture industry and the economic benefits that it has brought to many countries cannot be underestimated5 and minimising the escapes of non-native aquaculture species must be a high priority for resource managers, conservationists and the aquaculture industry3.

The natural distribution of the turbot includes coastal waters of all European countries in which it is farmed. However, turbot has been introduced to other regions (notably Chile in the late 1980s) and, more recently, China6. In China it is one of the certified by the National Certification Committee of Aquatic Wild and Bred Varieties (NCCA) genetically improved fish breeds and alien species for commercial aquaculture5.


  1. P. Arechavala-Lopez, K. Toledo-Guedes, D. Izquierdo-Gomez, T. Šegvić-Bubić & P. Sanchez-Jerez. 2018. Implications of Sea Bream and Sea Bass Escapes for Sustainable Aquaculture Management: A Review of Interactions, Risks and Consequences, Reviews in Fisheries Science & Aquaculture, 26 (2), 214-234
  2. ICES
  3. Cook, E.J et al, 2007. Non-Native Aquaculture Species Releases: Implications for Aquatic Ecosystems. Chapter 5 in Aquaculture in the Ecosystem, pp155-184
  4. Prado, F.D., Vera, M., Hermida, M., Blanco, A., Bouza, C., Maes, G.E., Volckaert, F.A.M., Martínez, P. and AquaTrace Consortium, 2018. Tracing the genetic impact of farmed turbot Scophthalmus maximus on wild populations. Aquaculture Environment Interactions. 10, 447-463
  5. FAO
  6. FAO