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A pilot study of Noah's Ark shell (Arca noae Linnaeus, 1758)and Seabass (Dicentrarchus labrax, Linnaeus, 1758)Integrated Aquaculture in Zone 1, Zadar County, Croatia

Noah's Ark shell (Arca noae Linnaeus, 1758), a species of bivalve byssal Mediterranean mollusc in the family Arcidae, is one of the most commercially exploited shellfish species in the Adriatic Sea. Inspite of no reliable data on catch quantities of A. noae in Croatia, there are indications of overexploitation in several areas of the region. Growing market demands, limited endemic populations, and a high market price make A. noae a possible candidate for introduction into local aquaculture. A worldwide trend for increased sustainability and mitigation of the environmental impact through Integrated Multi-trophic Aquaculture (IMTA) is constantly considering new species through applied research and production. In this study we evaluated several production parameters for A. noae under experimental IMTA conditions in the Adriatic Sea (Croatia). Arks were monitored over a course of one year in three locations: control location in their natural habitat (Pasman channel), and 2 locations at sea bass farm near Pasman Island (at 0 and 60m from cages). Lengths of 870 A. noae collected in the Pasman channel were measured, marked with mollusc tags (Hall print), randomly divided into groups, placed in nylon nets and suspended at designated locations. Lengths of A. noae used in experiment ranged from 31.4 - 83.1 mm. Every three months, lengths of A. noae were evaluated for survival/mortality rate and growth, while condition index (CI) was monitored on monthly basis. Data analysis showed high mortality during the first 3 months of growth with only 177 arks surviving after 1 year (20.3%). Initial high mortality can be attributed to stress during the collection and marking process. Mean annual growth was highest on location close to the fish cages (x=2.53followed by the location in Pasman channel (x=1.31and 60m away from cages (x=1.06Monthly mean CI values ranged from 18.79 (Site 3, December 2008) to 27.37 (Site 2, June 2009). Samples collected from the control site had significantly lower CI values than those collected at fish farm in 4 of 6 sampling months for which differences between sites were detected. These results are in compliance with previous studies which described A. noae as slow growing species that require more than 7 years to reach the commercial length of over 50mm. Our study suggests that arks may be influenced by fish farming effluents, resulting in enhanced feeding habits and increased CI values. This is in concordance with previous IMTA studies in the Mediterranean, suggesting a great potential for development of sustainable aquaculture under IMTA principles. Our preliminary data warrant further research in this area in order to assess whether A. noae is a suitable candidate for integrated aquaculture in the eastern Adriatic.

Arca noae; seabass; integrated aquaculture; Croatia

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