Stimulating investment in pearl farming in ... - World Fish Center

Figure 11. Intermediate culture trays with spat glued onto the base with “Superglue”.After lids are fitted the trays are suspended from long lines.Intermediate culture can also be a stepping stone to helical culture. In helical culture,small shell are drilled close to the byssal opening, threaded onto low breaking strainfishing line (15 lb is used at the WorldFish Research Centre) and then wound into thegroove of a 1 m length of laid rope, which is then placed inside a protective meshsleeve. We have found that spat can be drilled for helical culture at around 25-30mm, suggesting that most spat will require only three-four months of intermediateculture (e.g. Figure 12, 13). Helical culture provides enhanced growth conditionsthrough improved water movement and still provides protection from fish predation.5.2 Hatchery-reared spat in intermediate grow-outA single experiment was undertaken in 1999 to compare the growth and survival ofhatchery-reared and wild-caught spat. In each case, spat were glued inside plastictrays and incubated at random distances along a longline. Interpretation of survivaldata is complicated because the wild-caught spat suffered an unusually high rate ofmortality in the early stages of growth (Figure 14). On average, hatchery-reared spatgrew at a slightly but significantly slower rate than wild-caught spat (Figure 11).These data suggest that, should implantation of hatchery-reared spat prove successful,this could be a realistic alternative to reliance on wild capture.15