Effect of emersion time on growth, mortality and quality of Pacific oysters (Crassostrea gigas, Thunberg 1973) reared in a suspended system in a lagoon in Northern Italy

To assess the effect of emersion time on growth, mortality and quality, 4320 triploid oysters were glued to suspended ropes in a plant located in Sacca degli Scardovari, a Northern Italian lagoon on the Po delta. The oysters were subjected to three emersion systems (10 ropes/system): the farm standard, i.e. 14 emersion hours every 4 days during the first 4 months and 10 emersion hours every 2 days during the last 4 months of trial; long, 14 emersion hours per day; short, 7 emersion hours per day. At attachment, oysters exhibited an average weight of 6.04 ± 2.63 g and a length of 39.8 ± 8.38 mm. Eight months after attachment, mortality was significantly lower in the case of the standard system and higher in both short and long emersion systems, i.e. 44.3% vs. 66.8% and 63.3%, respectively (P ≤ .001). At harvest, oyster biometric and rheological traits, proximate composition and fatty acid profile did not change with the emersion system, with few exceptions. The muscles of oysters submitted to short emersion showed lower hardness than those submitted to long and standard emersion systems (1027 g vs. 1422 g and 1430 g; P ≤ .05). Furthermore, oysters under the long emersion system had greater cohesiveness than those of the standard system (0.53 vs. 0.49; P ≤ .05). In conclusions, oysters reached the commercial size in 8 months, which makes Sacca degli Scardovari a promising site for oyster farming. Emersion time scarcely influenced oyster growth and quality, but had a large impact on oyster mortality.