Previous experiments have shown that the grow-out method affects the growth and survival of bivalves. The shape and size of the grow-out structures play a major role, particularly for commercially valuable species such as Pinctada fucata.

Two Comparative Experiments

Researchers conducted two trials to measure growth and survival rates of oysters according to mesh type and size.

In the first experiment, P. fucata juveniles (mean DVH 36.2 ± 0.1 mm, n = 90) were placed for three months in pyramid-shaped nets with mesh sizes of 1 mm, 4.5 mm, and 9 mm.

The results showed marked differences (F2,177 = 385.5, P < 0.001):

• 1 mm mesh: mean DVH 37.8 ± 0.4 mm
• 4.5 mm mesh: mean DVH 48.4 ± 0.4 mm
• 9 mm mesh: mean DVH 51.7 ± 0.4 mm

Survival rate was 100% in all cases except for 1 mm nets, where it dropped to 92%.

Results of the Second Experiment

In the second trial, juveniles (mean DVH 49.6 ± 0.4 mm, n = 90) were placed in four different structures: 5 mm panels, 15 mm panels, 4.5 mm panels, and 9 mm bags.

After 11 months:

• 15 mm mesh panels: mean DVH 73.8 ± 0.9 mm
• 9 mm bags: mean DVH 71.9 ± 0.8 mm
• 4.5 mm bags: mean DVH 70.0 ± 0.7 mm
• 5 mm panels: mean DVH 67.0 ± 1 mm (lowest growth)

Survival rate remained high, between 95% and 100%, with no significant variation according to grow-out conditions (p > 0.05).

Conclusion: A Necessary Compromise

These results confirm that mesh size influences growth: smaller meshes promote fouling, reduce water circulation, and limit nutrient supply, thereby degrading environmental quality. To optimize oyster growth, it is recommended to use larger meshes that allow better water flow and adequate feeding.