The role of vertical barotropic and baroclinic tidal forcing in the aggregation and dispersion of ichthyoplankton in the Southern Gulf of Mexico was analyzed in this study. Samplings of ichthyoplankton and the determination of hydrographic parameters were performed during September 1992 at a single point of 180 m depth, near the shelf break (19º32'N - 92º38.5'W). A 24 h CTD yo-yoing casting and biological samples were taken every 2 h and these measurements were combined with water velocity and density simulations from the Regional Ocean Model System (ROMS). One thermocline and two haloclines were depicted. The Froude number increased with a 2 h lag with respect to the maximal barotropic tide, suggesting the existence of a baroclinic tide. Aggregation and dispersion of the ichthyoplankton showed vertical oscillations in the abundance and the numbers of taxa and larvae with a 5 h lag with respect to the maximal barotropic tide and were in phase with the thermocline oscillation. The vertical oscillation was attributed to a hydraulic control forced by the internal tide.
Se describe el desarrollo larvario de Hemicaranx amblyrhynchus con especímenes capturados en el sur del Golfo de México. Los ejemplares presentaron tallás desde 1.87 mm hasta 16.43 mm. Los ejemplares más pequeños presentan una cresta supraoccipital aserrada que se distingue todavía en el espécimen de 5.7 mm de LP y desaparece en los de talla superior. El cuerpo es moderadamente alto en la preflexión y aumenta ligeramente durante el desarrollo. Las aletas dorsal y anal son visibles a partir del espécimen de 2.65 mm de LN; el número de espinas y radios está casi completo alrededor de los 9.0 mm LP. Las larvas de H. amblyrhynchus pueden reconocerse por una mancha de pigmentos en la punta del hocico, que está confonnada, entre otros, por melanóforos en el palatino.
A simple technique for otolith of larval fishes is described. After fixing the otolith with some resin and drying, lift one edge of the resin and add 1-2 drops of xylene. The otolith becomes transparent and allows counting the growth rings before the xylene evaporates.
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