Protozoan and metazoan symbionts of natural and maricultured populations of commercial shrimp from the northwestern coast of the Gulf of Mexico.

Natural and cultured populations of P. aztecus and P. setiferus and cultured populations of P. strlirostris and P. vannamei were examinied for ecto- and endosymbionts. The 18 symbionts which follow were identified in the hosts: Epistylis sp., Zoothamnium sp., and Lagenophyrs sp. (peritrichs); Acineta sp. (a suctorian), Nosema nelsoni, Pleistophora penaei, and Thelohania penaei (microsporidians); Nematopsis sp. and Cephalolobus penaeus (gregarines); Opecoeloides fimbriatus (a trematode); Prochristianella penaei, Parachristianella dimegacantha, Parachristianella monomegacantha, lecanicaphalid larvae, and cycophyllidean larvae (cestodes); and Spirocamallanus pereirai, Thynnascaris sp., and unidentified larvae (nematodes). New host records were established for Epistylis sp. and Acineta sp. (P. stylorostris) and for P. monomegancantha and S. pereirai (P. aztecus); and the ranges of C. penaeus, P. dimegacantha, P. monomegacantha, lecanicephalid larvae, Thynnascaris sp., and S. pereirai were extended to the west or southwest. Larvae of an unidentified cyclophyllidean cestode were recovered from P. aztecus and P. setiferus. This is the first report of a cyclophyllidean from penaeid hosts.