Friday, 13 November 2009
Penaeid shrimp (Farfantepenaeus aztecus, F. duorarum, and Litopenaeus setiferus) are commercially important coastal and estuarine species along the United States East and Gulf coasts. Field studies indicate that postlarvae migrate from the larval development habitats on the continental shelf to juvenile nursery habitats in estuaries during nighttime flood tides, but the behaviors that underlie this migration are largely unknown. The objective of this work was to design and test an experimental setup for recording endogenous activity rhythms in Penaeid shrimp postlarvae and juveniles so that the role of endogenous rhythms during the migration could be evaluated. Groups of 30 postlarvae or individual juveniles were placed in 8×8×25 cm Plexiglas columns in a dark, temperature-controlled room and in front of an infrared emitting light box. The light box was constructed of 1.25 cm thick plywood, lined with aluminum foil, illuminated with a 3.66 m white rope light, and fitted with an infrared transmitting Plexiglas panel to filter out visible wavelengths. Experiments were recorded to an external hard drive using a pan/tilt/zoom digital networking camera. For the thin, clear postlarvae, a 1000 µm sieve was placed between the column and light box to improve visibility. Swimming activity was quantified at 30 min intervals by counting either the number of postlarvae in the top 1/3 of the column or the number of times a juvenile ascended from the bottom. Data were analyzed using time-series analysis techniques. Preliminary data indicate that pink shrimp postlarvae from Florida Bay may exhibit a semi-lunar activity rhythm with maximum activity during nighttime flood tides, whereas juveniles from Country Club Creek in Savannah, Georgia may be most active during slack water at both high and low tides.
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