The present project represents the final step of previous studies on the farming of the boring bivalve Pholas dactylus (common piddock). The aims were: a) to test artificial substrates made of different materials for the settlement and subsequent on-growing of this species in order to give the shells a different colour and easily distinguish the farmed individuals from the wild ones; b) to identify the most suitable material in terms of density and growth rate; c) to check for the presence of contaminants in the flesh of the reared specimens; and d) to conduct a market survey at some local restaurateurs to check their reaction towards the farmed product. The study lasted for 3 plus 1 derogation years (2007-2011). It was carried out inside the Portonovo artificial reef (central Adriatic Sea) at 11 m depth and 500-600 m from the shoreline. This area is characterized by an abundant wild population of P. dactylus. Twenty-four grey coal-ash blocks (CCC) and 24 red marble powder modules (PMR) were deployed in June 2008. The first settlement of P. dactylus occurred on both substrates in October 2008. During that survey and in the 6 following ones two CCC and two PMR blocks were collected. Individual shell length (SL) and total weight (TW) of the specimens were recorded. Mean density (N. ind. m-2), size-frequency distribution and length-weight relationships (SL/TW) were calculated for each kind of modules. The Bhatthacharia method was used to identify the different pseudo-cohorts in the size-frequency distributions. Growth rates and total mortality (Z) were calculated on the main pseudo-cohort. In addition, heavy metal contents were measured in the edible parts of the bivalves. The occurrence of the first specimens of P. dactylus in October 2008 demonstrated that the settlement started at the end of August - beginning of September, according to what observed in previous studies (Fabi et al., 2000). The specimens recorded on CCC and PMR modules always showed similar average SL, densities, and growth rates. On the other hand, the individuals settled on PMR modules showed a greater Z and, considering the same SL, were heavier than those collected from CCC blocks. As regards the shell colour, initially the specimens settled on the two substrates were easily distinguishable, but the difference disappeared on time. However, the farmed bivalves maintained a grey colour which made them different from the wild ones. Pb, Cd, and Hg contents in the flesh of farmed specimens were always lower than the limits reported by the EC Reg. 629/2008, while the values of As, Cu, Cr, Ni, and Zn were similar or lower than those reported for Mytilus galloprovincialis in the same area (Fattorini et al., 2008). Basing on the above results and taking into account that the two typologies of modules had same construction cost, it can be stated that both of them are suitable for the extensive farming of P. dactylus.
La ricerca rappresenta la fase finale di una serie di studi concernenti l'allevamento del bivalve fossorio Pholas dactylus (dattero bianco) e aveva i seguenti scopi: a) testare moduli artificiali per l'insediamento di questo bivalve costruiti con materiali differenti per verificare la possibi¬lità di apportare alle valve una colorazione diversa da quella naturale, innocua per gli animali e per il consumatore, per distinguere più facilmente il prodotto allevato da quello selva¬tico; b) identificare il materiale più idoneo alla specie in termini di densità e crescita; c) verificare l'eventuale presenza di contaminanti nelle carni degli esemplari allevati; d) condurre un'indagine di mercato per verificare le reazioni dei ristoratori nei confronti del prodotto allevato. Lo studio ha avuto una durata di 3 anni più 1 di proroga (2007-2011). La ricerca è stata condotta nella barriera artificiale situata della baia di Portonovo (medio Adriatico), a 500-600 m dalla costa (prof. 11 m). A giu¬gno 2008 sono stati immersi 24 moduli in composto cenere di car¬bone (CCC), già sperimentati in precedenza, e 24 moduli in polvere di marmo rosso (PMR). Il primo insediamento di P. dactylus è stato rilevato nell'ottobre 2008. In quel survey e nei 6 successivi venivano prelevati 2 moduli per ogni tipologia di substrato e venivano registrati lunghezza della conchiglia (LC) e peso fresco (Pt) di ciascun esemplare. Per ogni tipologia di substrato sono state calcolate: densità media (N. ind. m-2), distribuzione di frequenza delle lunghezze e curve di regressione LC/Pt. Le distribuzioni di frequenza delle taglie sono state suddivise nelle varie pseudocoorti tramite il metodo Bhatthacharia. Per la pseudocoorte principale identificata per ciascuna tipologia sono stati stimati tassi di crescita giornalieri e mortalità totale (Z). Negli ultimi 4 survey sono stati anche ricercati alcuni metalli pesanti nelle parti edibili di circa 20 esemplari provenienti dai moduli CCC e PMR. Il fatto che i primi individui di P. dactylus siano stati osservati nell'ottobre 2008 dimostra che l'insediamento era iniziato intorno a fine agosto - inizio settembre, in accordo con quanto osservato precedentemente (Fabi et al., 2000). Gli esemplari insediati sui moduli CCC e PMR hanno sempre mostrato taglie medie, densità e tassi di crescita medi simili, mentre Z è risultata superiore sui moduli PMR. A parità di taglia, gli individui insediati sui moduli PMR hanno raggiunto un peso superiore a quelli rinvenuti sui moduli CCC. Riguardo la colorazione delle valve, all'inizio gli esemplari provenienti dalle due tipologie di substrato erano facilmente distinguibili, ma con il tempo questa differenza è andata scomparendo. Comunque, i bivalvi avevano mantenuto un colore grigio che li rendeva ancora riconoscibili da quelli selvatici, come convalidato dai ristoratori durante l'indagine di mercato. Questi ultimi hanno anche ap¬prezzato consistenza e sapore delle carni. Le analisi di bioaccumulo hanno mostrato valori inferiori a quelli previsti dal Reg. CE 629/2008 per Pb, Cd e Hg, mentre As, Cu, Ni, Zn e Cr sono risultati inferiori o simili a quelli riportati da Fattorini et al. (2008) per mitili provenienti dalla stessa zona. Considerando quanto esposto sinora e gli stessi costi di realizzazione, entrambe le ti-pologie di moduli sono ritenute idonee per l'allevamento estensivo di P. dactylus.
Allevamento del dattero bianco Pholas dactylus su substrati artificiali: fase finale di sperimentazione. Rapporto finale
Fabi G;Punzo E;Scarcella G;Spagnolo A
2011
Abstract
The present project represents the final step of previous studies on the farming of the boring bivalve Pholas dactylus (common piddock). The aims were: a) to test artificial substrates made of different materials for the settlement and subsequent on-growing of this species in order to give the shells a different colour and easily distinguish the farmed individuals from the wild ones; b) to identify the most suitable material in terms of density and growth rate; c) to check for the presence of contaminants in the flesh of the reared specimens; and d) to conduct a market survey at some local restaurateurs to check their reaction towards the farmed product. The study lasted for 3 plus 1 derogation years (2007-2011). It was carried out inside the Portonovo artificial reef (central Adriatic Sea) at 11 m depth and 500-600 m from the shoreline. This area is characterized by an abundant wild population of P. dactylus. Twenty-four grey coal-ash blocks (CCC) and 24 red marble powder modules (PMR) were deployed in June 2008. The first settlement of P. dactylus occurred on both substrates in October 2008. During that survey and in the 6 following ones two CCC and two PMR blocks were collected. Individual shell length (SL) and total weight (TW) of the specimens were recorded. Mean density (N. ind. m-2), size-frequency distribution and length-weight relationships (SL/TW) were calculated for each kind of modules. The Bhatthacharia method was used to identify the different pseudo-cohorts in the size-frequency distributions. Growth rates and total mortality (Z) were calculated on the main pseudo-cohort. In addition, heavy metal contents were measured in the edible parts of the bivalves. The occurrence of the first specimens of P. dactylus in October 2008 demonstrated that the settlement started at the end of August - beginning of September, according to what observed in previous studies (Fabi et al., 2000). The specimens recorded on CCC and PMR modules always showed similar average SL, densities, and growth rates. On the other hand, the individuals settled on PMR modules showed a greater Z and, considering the same SL, were heavier than those collected from CCC blocks. As regards the shell colour, initially the specimens settled on the two substrates were easily distinguishable, but the difference disappeared on time. However, the farmed bivalves maintained a grey colour which made them different from the wild ones. Pb, Cd, and Hg contents in the flesh of farmed specimens were always lower than the limits reported by the EC Reg. 629/2008, while the values of As, Cu, Cr, Ni, and Zn were similar or lower than those reported for Mytilus galloprovincialis in the same area (Fattorini et al., 2008). Basing on the above results and taking into account that the two typologies of modules had same construction cost, it can be stated that both of them are suitable for the extensive farming of P. dactylus.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
