Prevalence and survival of escaped European seabass Dicentrarchus labrax in Cyprus identified using genetic markers

C Brown,D Miltiadou,Cs Tsigenopoulos

doi:10.3354/aei00135

C Brown, D Miltiadou + Show 1 more

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https://doi.org/10.3354/aei00135

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Abstract

The escape of European seabass Dicentrarchus labrax (L.) from fish farms is consid- ered to be a widespread problem in the Mediterranean area, where this species is produced in large quantities in offshore cages. Whilst estimates of the number of escaped seabass in the wild have been made previously, the actual distribution, long-term survival and the potential effects on native populations remain largely unknown. This study characterises the genetic profiles of all contemporary and some historic aquaculture sources of European seabass in Cyprus and uses these profiles to identify escaped fish in seabass collected from the wild around the island. Signif- icant differences in the microsatellite and mitochondrial DNA marker profiles were found between farmed and wild fish. The number of escapees identified was 15% of the total number of wild-caught fish sampled. However, escapees were not equally distributed; at one location ~70% of wild-caught fish were escapees while in other areas escapees only accounted for up to 4%. Escapees were present in all size classes of fish, but the majority were of commercial size (300�500 g) typical of seabass farmed in seacages. This indicates that they may have escaped recently and during normal aquaculture operations as no escape event was reported in the course of the study. Two large, egg-bearing females and some juvenile fish were also classified as escapees, which suggests that long-term survival and interbreeding with wild fish is possible in Cypriot waters.

Highlights

The escape of fish from sea-based aquaculture installations is recognised as a problem due to the potential impact of cultured fish on wild populations in terms of disease (Johansen et al 2011), competition for food (Abrantes et al 2011) and interbreeding (Bourret et al 2011)
An indicative estimate of escapee frequency can be found in gilthead seabream Sparus aurata — a species commonly farmed together with seabass using the same equipment and methods —which were found to approximate 13% of wild fish sampled in Croatia (Šegvić-Bubić et al 2011)
The results of this study show conclusive evidence of the presence of a wild population of European seabass in Cypriot waters that is genetically distinct from fish originating from aquaculture sources

Summary

Introduction

The escape of fish from sea-based aquaculture installations is recognised as a problem due to the potential impact of cultured fish on wild populations in terms of disease (Johansen et al 2011), competition for food (Abrantes et al 2011) and interbreeding (Bourret et al 2011). There are frequent, small losses of fish during harvesting, transfers and maintenance work which could be significant in the long term (Dempster et al 2007). Despite frequent evidence of large numbers of escaped seabass close to fish farms Dempster et al 2002, ToledoGuedes et al 2009), there are no reliable estimates of escapee frequency in the wild, of long-term survival or of the level of interaction with wild fish, these are considered research priorities (Youngson et al 2001, Haffray et al 2007). An indicative estimate of escapee frequency can be found in gilthead seabream Sparus aurata — a species commonly farmed together with seabass using the same equipment and methods —which were found to approximate 13% of wild fish sampled in Croatia (Šegvić-Bubić et al 2011). ‘escape by spawning’ has been highlighted as a potentially important source of farm-origin fish from Mediterranean aquaculture as a consequence of fish increasingly being held in seacages beyond sexual maturation (Dimitriou et al 2007, Somarakis et al 2013)

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