Jaime R. Alvarado Bremer (TAMU - G) and Jim Ditty (NMFS)

Prediction of year class strength, accurate assessment of important  nursery habitat, development of water and wetland management strategies, and decisions regarding the effect of coastal development on shrimp populations require correct identification of all life stages of shrimp.  While separation of adult brown shrimp ( Farfantepenaeus aztecus ) from pink shrimp ( F. duorarum ) is relatively easy, separation of their postlarval and early juvenile stages remains problematic.  Characters for separating specimens between 10-25 mm TL are unreliable and depend on subjective interpretation of third pereopod (i.e., leg) length relative to the eye, rostral shape, uropod coloration, and/or early changes in the development of genitalia.  Intra-specific variability in morphology imposed by spatial, temporal, and environmental differences compound difficulties in separating postlarvae of these two species.  The current      descriptive literature has limited value for separating taxa because most studies do not consider the high degree of intra-specific morphological variability.

This two-year Texas Sea Grant funded project takes a dual approach for identifying, assessing, and verifying differences between species that minimizes the impact of morphological variability due to extrinsic factors, yet provides confirmation of specimen identification (ID).  Our procedure combines ontogenetic scaling techniques with ID verification by molecular genetic testing.  Project goals are two-fold: 1) develop an ontogenetic index that permits rapid and reliable separation of post-larval brown from pink shrimp, yet allows screening of large numbers of specimens; and, 2) develop relatively inexpensive assays to verify the identity of these two closely related species of shrimp.  Ultimately, this information will contribute to more accurate estimates of year class strength, improve predictive capabilities, and provide fishery managers with better information upon which to base recommendations regarding potential annual yield and regulation of the shrimp fishery.