Factors influencing half-pearl (mabe) production and quality in the red abalone Haliotis rufescens

The factors influencing half-pearl (mabe) production in the red abalone Haliotis rufescens were investigated, as a strategy to optimize the technology for the development of a pearling industry in Chile. The effects of abalone size (small, large), implant position (dorsal, central, ventral and their combinations), and number of nuclei (one, two, three) were analysed on the quantity, thickness of the nacre layer and quality (shape, colour, lustre, defects) of the mabe produced. The size of abalone did not exert a clear influence on the quantity and quality of mabe, but the position on the shell (firstly) and number of nuclei (secondly) did. More mabe, with thicker nacre, brighter lustre and fewer defects occurred in small or large abalone implanted with only one nucleus on dorsal position. In contrast, small and large abalone implanted in the ventral position formed less mabe, with thinner nacre, poor lustre and more defects. This likely occurs because mantle tissue folds at the ventral position and does not always cover the nucleus, leaving it partially or totally exposed. Most of the pearls were categories AA in small abalone and A in large abalone; only three AAA gems were produced in large abalone with one nucleus on dorsal position or with three nuclei (DCV). Based on these results, we recommend implanting abalone at 60-100 mm shell length, with only one nucleus on the dorsal position.