Using coded wire tags to assess growth rates of individual grass shrimp Palaemonetes pugio

The grass shrimp Palaemonetes pugio is an important prey item for many species including those of commercial value. Growth may provide evidence of habitat quality or organismal health. For accurate results, individual grass shrimp should be monitored to determine growth. Coded wire tags have been used successfully to identify individuals of many larger species; however, the effect of these tags on grass shrimp growth has not yet been determined. The purpose of this study was to determine this effect and to compare growth of unparasitized grass shrimp to those parasitized by the isopod Probopyrus pandalicola. This study was conducted using tidally influenced estuarine mesocosms at NOAA's Center for Coastal Environmental Health and Bimolecular Research in Charleston, SC. Grass shrimp were collected from Leadenwah Creek, SC. Initial total length (mm) and weight (g) were recorded for each individual, and they were placed into the following treatments with the control being unparasitized untagged shrimp (n=25): tagged unparasitized shrimp (UPS, n=75) and tagged parasitized shrimp (PS, n=38). Grass shrimp from each treatment were placed in each of 3 mesocosms for 42 d. Subsequently, grass shrimp final total lengths and weights were compared across treatments to assess growth. The tag does not affect growth expressed as either length or weight (p>0.05). UPS grew 19.35% in length and 57.14% in weight. PS only grew 1.37% in length and lost -4.55% in weight. There was a significant difference in growth in length and weight between UPS and PS (p<0.0001). These results reinforce the findings of Anderson (1977) who found that this parasite utilizes 6-10% of the daily energy of infected shrimp. In the future, we may add another stressor such as anthropogenic contaminants to determine its effect on individual growth.