| 5. | ||
| As larvae reach a shell width of 180 µm
and approach metamorphosis, the algae Rhodomonas sp. and Tetraselmis
suesica should be included in the diet. Greatest success through the
rather critical metamorphosis period was achieved when these foods were
supplied (Leighton, 1979).
Metamorphosis Larvae in the size range 200-220 µm develop eye spots and an extensible foot. These anatomical advances signal the onset of metamorphosis to the benthic juvenile form. This stage is especially critical to subsequent survival. Seldom have larvae held in pails or beakers succeeded through metamorphosis. Our best yields of postmetamorphic juveniles have been realized in nylon mesh bottom fiberglass vats or PVC and ABS pipe sections immersed in seawater within a larger reservoir (Leighton and Phleger, 1981; Leighton, 1991). Moderate aeration keeps food algae in suspension and creates a healthy environment for metamorphosing larvae. Some success has been achieved by releasing late stage larvae into a large tank supplied coarsely filtered seawater. A "spatting pond" is described by Bourne et al., (1989) in which various substrates (shell, rock and plastic netting) are included. The lack of control of biotic factors inherent in this approach would likely result in varying yields. However, it is expected future study of similar systems will guide development of highly efficient larval setting programs.
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 Mesh bottom fiberglass pot immersed in a  Juvenile rock scallops harvested from the system shown above.
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