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• Title: Effect of Depth and Stocking Density on Growth and Retrieval of the Postlarval Lion's Paw Scallop, Nodipecten Nodosus (Linnaeus, 1758).
• Author : Journal of Shellfish Research
• Release Date : January 01, 2004
• Genre: Life Sciences,Books,Science & Nature,
• Pages : * pages
• Size : 228 KB

Description

ABSTRACT Coastal areas of southern Brazil are experiencing an intense development of bivalve farming, and the lion's paw scallop, Nodipecten nodosus (Linnaeus, 1758), is a promising aquaculture species. An important but poorly understood oceanographic feature described for the inner continental shelf of the southeastern Brazilian coast is the seasonal subsurface intrusion of cold and phytoplankton-rich South Atlantic Central Water (SACW) during summer-autumn, it was not clear, however, if these intrusions could affect near-shore coastal areas off Santa Catarina State, where aquaculture activities are now expanding, nor if they could affect growth and survival of bivalves under culture conditions. It was therefore hypothesized that intrusions of SACW with higher food levels and lower temperature would result in depth-related differences in environmental factors that would affect bivalve growth. One experiment was carried out in summer-early autumn (March-April 2001), a period of possible SACW intrusion in a coastal site, and a second experiment was carried out in late autumn-early winter (June July 2001) when the water column would possibly be homogeneous. In both experiments, hatchery-produced postlarval N. nodosus (0.4 mm) were deployed in the sea based nursery 12-15 days after settlement and retrieved 26-27 days later. Postlarvae were attached to Netlon collectors, placed inside nylon bags, and hung on a subsurface long-line at 4 and 12 m. The effects of deploying postlarvae at two densities (340 and 150 scallops/spat bag) were also investigated. Subsurface intrusions of cold and phytoplankton-rich SACW occurred at a near-shore (0.5 km) coastal site in late summer-early autumn but not in late autumn-early winter. The influence of SACW resulted in oscillating temperatures (17.8-27.2[degrees]C) on a short Lime-scale and in high particulate inorganic matter (PIM), which reduced postlarval growth at 12 m compared with 4 m. but did not affect survival. When SACW was not present, there were no depth-related differences. Postlarvae cultured at high density displayed slightly smaller shell heights at both depths than postlarvae kept at low density but displayed similar survival, resulting in higher yields (no. spat/bag). The use of a subsurface long-line for deploying hatchery-produced postlarvae (0.4 mm) resulted in percentage retrievals of about 70-80%, regardless of treatment and season, values that are higher than in previous studies. There is a good potential for growing N. nodosus in sea-based nurseries in coastal areas of southern Brazil, and growth can be optimized by seasonally adjusting culture depth. KEY WORDS: environmental factors, growth, Nodipecten nodosus, nursery culture, postlarvae, scallop, survival

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