Impact of Culture Period on Quality of Image Pearls Produced by the Freshwater Mussel, Lamellidens marginalis, in Bangladesh

ABSTRACT Pearls are gems produced by biological processes within the living tissues of molluscs. Image pearls are a form of blister pearl that portray a design or image such as a bird, fish, flower, goddess, etc. To achieve this, a paraffin wax mold is inserted between the shell and the mantle of a freshwater mussel and subsequent nacre coverage produces an image pearl after an appropriate culture period for the mussel. The optimum culture period has not yet been determined to maximize the quality of image pearls produced in Bangladesh, and this knowledge gap was addressed in this study. Image pearl production using the freshwater mussel Lamellidens marginalis was conducted over three culture periods (T 1 = 7 mo, T 2 = 9 mo, and T 3 = 11 mo). A total of 3,150 mussels were implanted with 2.5 × 1.5 cm2 paraffin wax molds, with 1,050 mussels allocated to each treatment, which had five replicates. Survival and pearl production rate of mussels were negatively correlated with culture period. Survival and pearl production rate were 14.7%, 12.3%, and 11.9% for mussels cultured for 7, 9, and 11 mo, respectively. The thicknesses of the nacre making up the image pearl and pearl luster were both improved with longer culture periods. The highest quality pearls with a mean nacre thickness of 0.71 mm were produced after 11 mo. Pearls produced after 11 mo also had the highest luster (40.05 lux) compared with pearls cultured for 7 mo (12.85 lux) or 9 mo (30.2 lux). There were statistically significant differences at the P < 0.05 level in survival rate F (2, 12) = 9.40, P = 0.004 and nacre layer thickness F (2, 12) = 13.30, P = 0.001 between T 1 and T 3. The results indicated that image pearls with high luster and improved quality are produced after longer culture durations and confirms the influence of culture period on image pearl production and quality. Further research is required to improve image pearl production methods and pearl yield.