The farming of the greater amberjack (Seriola dumerili , Risso 1810) in the Mediterranean Sea started in the 1980s in a capture-based fashion ( FAO 2016-2021) . Nowadays, as a result of the industrial diversification of marine fish in Mediterranean aquaculture , the rearing cycle of S. dumerili is fully carried out in captivity . However, it was not until 2017, when the industrial production and commercialization started, with Spain and Greece as the main producers (FishSTAT), and more recently Croatia in 2019 (No data available in FishSTAT ; pers.obs Segvic-Bubic). Reared fish escaping from farms have a number of potential socio-economic and ecological implications, and some of them have been explored for Sparus aurata , Dicentrarchus labrax and Argyrosomus regius (Arechavala-Lopez et al., 2018).
T his research describes the first escape of S.dumerili in the Mediterranean and aims i ) to develop the identification techniques of the escaped individuals of S. dumerili , ii) to help understanding the potential influences of the escape events at a genetic and fisheries levels and, iii) to improve the aquaculture genetic management of the species.
Material and Methods
In the current research, captures of unusual individ uals of S.dumerili were detected via pictures posted in Facebook groups with fisheries interest. Data on c ommercial fisheries landings of the artisanal fleet based on the marina of Santa Pola (38º11’12’’N; 0º33’33’’W, Alicante, Spain), was explored to identify abnormal captures of the S. dumerili at a temporal level . Local Ecological Knowledge of fishermen was obtained via personal interviews on Facebook messenger, to better understand the behavior and dispersion of the escaped fish.
Following a simplified mammalian DNA isolation procedure, a total of 492 individuals were successfully genotyped with 15 micro satellite markers developed for S. dumerili (Renshaw et al. 2006, 2007) from 10 populations sampled in both, the Adriatic and Balearic Seas, covering different fish origins (wild, farmed and escaped). Genetic diversity, differentiation and structure for each population were calculated and assessed by using FSTAT 2.9.3, Arlequin v.3., FreeNA , Structure 2.3 and Adegenet package in R.
A photo of the left side of each fish was taken at 1m (orthogonal distance), with a photo camera set at 50mm focal length. A 50 cm ruler was included in each picture for body length measurement in ImageJ software. Quantification and visualization of fish shapes were conducted by means of geometric morphometrics , using a total of 21 landmarks (TpsDig 2 and MorphoJ software and geomorph R package). Eventually, differences between fish groups of different origins were explored with canonical analysis.
Results and conclusion
Arising from social media pictures and conversations/commentaries of fishermen, t he escaped fish was darker than wild ones and some fish presented deformities and/or wounds. Approximately two months after the escape event, the presence of escaped S. dumerili still could be observed in the escape area . The maximum dispersion attained up to 100 km to the south and 90 km to the north from the potential escape locations , namely San Pedro del Pinatar (Murcia) and Calpe (Alicante) , both in the SE of Spain. The captures of c ommercial and recreational fisheries were influenced by escaped fish . Significant g enetic differentiation between farmed and wild fish groups were observed where farmed fish were characterised with reduced number of alleles, allelic richness and expected heterozygosity . Minimum estimates of effective population size, which may serve as a conservative estimate for wildlife management, were for two order of magnitude smaller in farmed (̴ 3) than in wild (̴ 300) populations , implicating urgent need for genetic improvement of broodstock menagment
Morphological differences between wild and reared fish existed , with a striking difference in the mouth position , which showed upwards-oriented in reared fish, compared to a more horizontal position of wild fish.
In first term, fish escapes should be managed from a prevention perspective followed by mitigation and monitoring programs. T he development of a tool-kit to identify escaped individuals is suggested. The behaviour of escaped S. dumerili should be studied from a spatio-temporal, ecological, fisheries and management perspectives . In terms of aquaculture management, to increase the broodstock size it is suggested, in order to minimize inbreeding risks and potential genetic influences for the populations of wild counterparts.
Arechavala-Lopez , P., Toledo-Guedes, K., Izquierdo-Gomez, D., Šegvić-Bubić , T. and Sanchez -Jerez, P., 2018. Implications of sea bream and sea bass escapes for sustainable aquaculture management. Reviews in Fisheries Science & Aquaculture, 26, pp.214-234.
Cultured Aquatic Species Information Programme . Seriola dumerili. Cultured Aquatic Species Information Programme . Text by Jerez Herrera, S. and Vassallo Agius, R. In: FAO Fisheries Division [online]. Rome.
Renshaw, M.A., Patton, J.C., Rexroad 3rd., C.E., Gold, J.R., 2006. PCR primers fortrinucleotide and tetranucleotide microsatellites in greater amberjack, Serioladumerili. Mol. Ecol. Notes 6, 1162–1164.
Renshaw, M.A., Patton, J.C., Rexroad 3rd., C.E., Gold, J.R., 2007. Isolation andcharacterization of dinucleotide microsatellites in greater amberjack, Serioladumerili . Conserv. Genet. 8, 1009–1011.
This research has been funded by the projects AquaPop IP-2014-09-9050 (Croatian Science Fundation ) and GLORI A (GLObal change Resilience In Aquaculture: FBIOPLEAMAR20-05) . Eventually the authors would like to thank the personnel of the Santa Pola Fish market and the rearing facilities of CROMARIS (Croatia) and the Spanish division of the ANDROMEDA group.