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Ideal settlement substrate and effect of darkness on spat production of the mangrove cockle Anadara tuberculosa

Abstract:

The mangrove cockle (Anadara tuberculosa) is considered overharvested. Therefore, its spat production in hatchery is needed for aquaculture and restocking of natural banks. However, larval settlement and metamorphosis are critical phases that need to be further explored. The use of different substrates on the settlement and two photoperiods on spat production of A. tuberculosa were evaluated. Furthermore, its embryonic development is described. In the first experiment, the settlement and survival of pediveliger larvae distributed in a completely dark experimental system provided with different diameters natural substrates: sand (≤500 μm), sand (≤200 μm), crushed shells of A. tuberculosa (≤200 μm), a mixture of sand and crushed shells of A. tuberculosa (≤200 μm), not-crushed shells of A. tuberculosa (5–10 mm), and nylon mesh (150 μm mesh size) were compared. In a second experiment, metamorphosed postlarvae were placed under 12 h light and 12 h dark (12 L: 12D) versus 0 h light and 24 h dark (0 L: 24D), to compare survival and growth. Additionally, a culture cycle from early larval stages until spat production under dark conditions was exanimated and described. The mesh base resulted the best substrate for a fast settlement and high larval survival. The photoperiod 0 L:24D enhanced spat growth compared to 12 L:12D. The average growth rate for shell height was 11.43 μm d−1 in the larval phase and 23.71 μm d−1 during postlarval phase. After metamorphosis, the larval growth increased rapidly until spat. A dark period and nylon mesh substrate should be considered as a preponderant factor in the massive spat production of A. tuberculosa.