Observations on the Ecology and Life Cycle of Prochristianella penaei Kruse (Cestoda: Trypanorhyncha)

Abstract

Examinations of Penaeus aztecus and P. setiferus from the Galveston Bay area show Prochristianella penaei plerocerci to be common in these shrimp, thus extending the known range of this tapeworm to the western Gulf of Mexico. Two years of repeated sampling of shrimp from Clear Lake, a secondary bay in the Galveston Bay system, showed patterns of infection which provided useful leads both to the ecological area where infection of shrimp occurs and the identity of the parasite's definitive host. The relationship found between shrimp size and incidence of infection, when considered with the known migratory habits of Penaeus aztecus and P. setiferus, suggests that these decapods are uninfected when they enter the bay and are usually infected by the time they leave. Since this pattern showed a rather brackish bay (1%o to 10%o) to be a probable site in which infection of shrimp takes place, it was assumed that (1) the first intermediate host of ProchristianeUa penaei also inhabits such areas and (2) the range of the elasmobranch final host includes low salinity areas, permitting completion of this cestode's life cycle. The latter point postulates a broad salinity tolerance range for the final host. Discovery of the adult tapeworm in Dasyatis sabina, a ray noted for the extent of its salinity tolerance, lends support to these assumptions. Despite our long acquaintance with penaeid shrimp (e.g., Linnaeus provided the first description of the white shrimp, Penaeus setiferus), and the continually increasing commercial importance of these animals during the last 40 years, thorough examinations of shrimp for parasites have not been reported prior to the Florida studies of Hutton et al. and Kruse, both in 1959. As a result, our present knowledge of the ecology and life cycles of shrimp parasites is slight. This situation is particularly true in the western Gulf of Mexico, one of the most productive shrimp habitats in the world. In 1959, Dr. Edward Chin brought to me for identification a small, white cyst in the digestive gland of a shrimp collected from Galveston Bay. The cyst proved to be the plerocercus stage of a trypanorhynch cestode identical to that described by Kruse (1959) as Prochristianella penaei. Since no information is available on the incidence of this parasite except in Florida waters, a survey was undertaken to determine the frequency with which the worm occurred in shrimp from the Galveston area. In addition, the dearth of information on trypanorhynch life cycles coupled with the need for a better understanding of shrimp ecology suggested a search for the undescribed Received for publication 2 December 1964. *Contribution No. 194, Bureau of Commercial Fisheries Biological Laboratory, Galveston, Texas. stages in the life history of P. penaei. The results of the survey work showed seasonal pa terns of infection which proved useful in ascertaining both the ecological area where inf ction of shrimp occurs and the identity of the parasite's definitive host. MATERIALS AND METHODS In selecting possible sites for regular sampling stations, consideration was given to the fact that both Penaeus aztecus, the brown shrimp, and P. setiferus, the white shrimp, are migratory in habit. T available life cycle information on these locally abundant species (Viosca, 1920; Weymouth, Lindner, and Anderson, 1933; and Burkenroad, 1934, 1939) indicates that spawning and larval development occur only offshore, the resulting postlarvae (about 0.5 inch in length) moving shoreward to bays, where they spend several months of rapid growth to subadult size (3 to 5 inches long) before migrating offshore again to attain adulthood and spawn. Thus, bays appear to provide important pasture areas for these animals prior to their return to the open waters of the Gulf of Mexico where they were spawned. Since Clear Lake, a secondary bay in the Galveston Bay complex (Fig. 1), was being sampled for shrimp fairly regularly by other workers at this lab ratory, and had been shown to harbor an abundance of both P. aztecus and P. setiferus (Chin, 1961), it was selected as an area for regular sampling. Monthly mean bottom temperatures for Clear Lake range from 10 to 30 C, and bottom salinity is usually between 1%o and 10%o. Offatts Bayou, another secondary bay in the Galveston Bay system, has a comparable temperature regime but a higher salinity range (15%o