5.4. NO EVIDENCE OF EGG ESCAPE FROM (Argyrosomus regius) AQUACULTURE UNDER
MEAGRE CURRENT
PRACTICES Cite this article as: Montero D, Ramírez B, Sanchez-Jerez P, Bayle-Sempere JT, Fernandez-Jover D, Fernández-Palacios H, Haroun R (2013) No evidence of egg escape from meagre (Argyrosomus regius) aquaculture under current practices. In: PREVENT ESCAPE Project Compendium. Chapter 5.4. Commission of the European Communities, 7th Research Framework Program. www.preventescape.eu ISBN: 978-82-14-05565-8
authors: Daniel Montero1, Besay Ramírez1, Pablo Sanchez-Jerez2, Just T. Bayle-Sempere2, Damian Fernandez-Jover2, Hipólito Fernández-Palacios1 & Ricardo Haroun1. University of Las Palmas de Gran Canaria, Spain, University of Alicante, Spain.
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INTRODUCTION Meagre (Argyrosomus regius; Figure 5.4.1) are distributed throughout the Mediterranean Sea, although they are uncommon in many parts of their range, although has not been very common in the wildness until it was farmed and some reiterate escape events increased its presence in the commercial catches during the last 5 years (Sánchez-Jerez et al. 2011). In the Atlantic, meagre are distributed from the southern coast of Sweden to the Guinean gulf, including Madeira and the Canary Islands. They are a large predatory fish and can grow up to 2 m and reach more than 50 kg. Meagre is an emerging species in Mediterranean aquaculture, due to its faster growth rate than other common Mediterranean aquaculture species such as European seabass or gilthead seabream. In 2010, 3887 t were produced in the European Union, with Spain growing 98% of this amount. Production is expected to increase in the future (FEAP 2011). Meagre are typically grown to a harvest size of 1.5 kg in sea cage aquaculture.
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Fig. 5.4.1. Meagre (Argyrosomus regius)
Meagre are a gonochoric species, with sexual maturation in the wild at 4 kg in males and 7.5 kg in females (Prista at al. 2007). In early spring, meagre migrate into estuarine water to spawn (QuĂŠmĂŠner at al. 2002). Juvenile fish remain in coastal waters for 2 or 3 years, before migrating to deeper waters as adults. Natural spawning of meagre broodstock in captivity has not been reported. Production of viable eggs has only been achieved through artificial reproduction with administration of luteinizing hormone releasing hormone agonist (LHRHa). Since meagre are an uncommon or rare species in some areas of the coastline where intensive culture is being developed, concern existed about the possibility that fertile, viable eggs could be released from sea cages. This could lead to increased recruitment rates and therefore increases in natural populations, which may have other cascading effects in coastal ecosystems. Further, other marine species mature precociously in aquaculture settings (e.g. Atlantic cod) at sizes much smaller than is usual in the wild.
OBJECTIVE We evaluated whether meagre were capable of spawning in sea cages under current day production conditions in fish farms in both Mediterranean Spain and the Canary Islands.
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METHODS To evaluate the degree of gonad development in industrial cultured meagre, we sampled meagre from sea cages in two locations where aquaculture of this species is increasing: the Canary Islands and the south-east coast of Spain. The potential for gonad maturation and spawning within sea cages was assessed based on whether we detected gonad maturation in market-size fish within sea cages.
Canary Islands study: A total of 138 cultivated meagre were collected from an industrial sea cage farm during the known spawning season of wild meagre (April – June). For each fish, size, weight and gonad weight and stage were recorded. In both studies, the extent of gonadal maturation was calculated using the gonadosomatic index (GSI). Gonads were classified macroscopically as immature (I), resting (II), ripe (III), ripe and running (IV), and spent (V; Holden and Raitt 1975). In addition, gonads collected during the Canary Islands study were removed and samples were fixed in 10% buffered formalin, dehydrated in a graded ethanol series and embedded in paraffin. Serial 4 µm sections were stained with haematoxylin and eosin (H&E) and slides produced from the gonads were analysed by microscopy.
Mediterranean study A total of 138 cultivated meagre were collected from an industrial sea cage farm during the known spawning season of wild meagre (April – June). For each fish, size, weight and gonad weight and stage were recorded. In both studies, the extent of gonadal maturation was calculated using the gonadosomatic index (GSI). Gonads were classified macroscopically as immature (I), resting (II), ripe (III), ripe and running (IV), and spent (V; Holden and Raitt 1975). In addition, gonads collected during the Canary Islands study were removed and samples were fixed in 10% buffered formalin, dehydrated in a graded ethanol series and embedded in paraffin. Serial 4 µm sections were stained with haematoxylin and eosin (H&E) and slides produced from the gonads were analysed by microscopy.
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RESULTS All fish sampled in sea cages at the Canary Islands had immature gonads in previtellogenic stages (Figure 5.4.2). Sampled fish were on average 1106 ± 318 g (mean ± SD), and gonad weights were particularly low (0.19 ± 0.1 g) indicating the juvenile status of these harvestsized fish. Sexual maturation was not detected in any of the individuals studied. No correlation was found between the gonadosomatic index and fish weight mainly due to the lack of sexual maturation within this size range (Figure 5.4.3). For the Mediterranean location, all sampled meagre had immature gonads, with gonadal maturity stage ranging between 1.03 (for fish 30 cm in body length) to 2.62 (for fish 77 cm in body length, Figure 5.4.4). The gonadosomatic index reflected the lack of gonad development in sea cages at commercial size (Figure 5.4.5).
Fig. 5.4.2. Gonads from a female meagre in Stage I (previtellogenic). Fish body weight = 1.7 kg.
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Fig. 5.4.3. Relationship between total fish weight and the gonadosomatic index for meagre (Argyrosomus regius) held in sea cages to commercial size in the Canary Islands. A polynomial regression line is included.
Fig. 5.4.4. Gonads of a meagre of 43 cm body length.
Fig. 5.4.5. Scatterplot of the gonadosomatic index (GSI) of meagre from two commercial Mediterranean farms.
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DISCUSSION The results obtained in both studies indicate that meagre have immature gonads in sea cages at present-day harvest sizes. Our study provides strong evidence that release of eggs from meagre produced to 1.5 kg in sea cages does not occur. Thus, we conclude that there no risk of egg escapes from meagre sea cage farms under current production practices. On occasion, large meagre (> 6 kg in body weight) are held in inland experimental conditions or found in industrial fish farms, either as part of normal production (Mediterranean Sea) or held as broodstock (Canary Institute of Marine Sciences). These fish have gonads in the final stage V of gonadal development (Figure 5.4.6 and 5.4.7). The existence of these larger animals in sea cages is an exceptional situation and may result from poor commercial management in specific farms and conditions. While spawning of these larger fish in sea cage environments has never been detected and appears unlikely given the need to chemically induce spawning in meagre broodstock, as production of larger fish becomes normal in the future, the possibility that large, mature fish can spawn in sea cages will require further assessment.
Fig. 5.4.7. Female gonads from a large meagre (71 cm body length).
Fig. 5.4.6. Gonads from a female meagre in Stage V (Vitellogenic). The female was kept in experimental conditions at the Canary Institute of Marine Sciences. Fish body weight = 10.4 kg.
RECOMMENDATION Even though spontaneous spawning has never been recorded in captivity, and natural spawning of meagre requires a combination of brackish and estuarine waters, a conservative recommendation to avoid any potential for ‘escape through spawning’ to occur for meagre is to limit culture to fish smaller than 5 kg body weight in sea cages.
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REFERENCES
CITED
FEAP (Federation of European Aquaculture Producers) (2011) www.FEAP.info Holden MJ, Raitt DFS (1975) Manual of fisheries science. Part 2. Methods of resource investigations and their application. FAO Fish. Tech. Pap. 115: 1-214. Prista N, Costa JL, Costa MJ, Jones CM (2007) New methodology for studying large valuable fish in data poor situations: commercial mark-recapture of meagre Argyrosomus regius in the southern coast of Portugal. ICES CM 2007/O:43. ICES, 18p. Quéméner L (2002) Le Maigre Commun (Argyrosomus regius) – Biologie, Pêche, Marché et Potentiel Aquacole. Ifremer, Plouzané. 31 pp. Sanchez-Jerez P, Izquierdo, D, Arechavala-Lopez, P, Bayle-Sempere, JT, Fernandez-Jover, D, Valero-Rodriguez, JM, Dempster, T (2011). Escapes of Argyrosomus regius in the mediterranean sea from fish farms: helping a rare species to be abundant in coastal areas. Proceedings of Aquaculture Europe Conference (EAS, Rhodes, Greece, 18-21 October 2011).
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