In vitro excystation of metacercariae of Microphallus turgidus under different physicochemical conditions.

This study examined the excystation of metacercarial cysts of Microphallus turgidus under varying conditions of temperature, NaCl concentration, and pH. Metacercarial cysts were dissected from abdominal muscle tissue of grass shrimp Palaemonetes pugio, and immediately incubated for 24 h under one of the following abiotic conditions: temperature (22, 26, 30, 34, 38, and 42 degrees C), NaCl concentrations (0.5, 0.6, 0.7, 0.8, and 0.9%), pH (2, 3, 4, 5, 6, 7, and 8), and percent excystation was recorded. The optimum in vitro excystation of metacercarial cysts occurred in 0.7% saline at 38 degrees C at pH 7; 92% of the cysts excysted under these conditions. Our results indicate that such a combination of extrinsic factors is provided by the definitive host for successful excystation of M. turgidus.

Prevalence, geographic distribution, and fitness effects of Microphallus turgidus (trematoda: Microphallidae) in grass shrimp (Palaemonetes spp.) from coastal Georgia.

Grass shrimp, Palaemonetes pugio Holthuis and P. vilgaris (Say), were collected at 11 localities along the coast of Georgia and surveyed for digenetic trematode metacercariae. The effect of trematode infection on grass shrimp fitness was also examined. Microphallus turgidas (Leigh) was the only trematode observed. The prevalence of metacercarial cysts of this parasite in P. pugio (75%) was higher than in P. vulgaris (24%), as were the mean intensity, abundance, and population density (no. cysts/cm host body length) of the parasite. Infected shrimp were found at every collection locality and parasite prevalence and density were greatest in P. pugio from higher salinity localities (> or = 20 parts per thousand [ppt]). There was no relation between host body size and parasite density in P. vulgaris, and parasite density increased with host body size in P. pugio, suggesting that the parasite does not affect host survival. There was no relation between parasite density and shrimp egg mass, but nonovigerous female P. pugio were more heavily infected than ovigerous ones. In addition, 1 metacercaria of M. turgidus in each of 2 specimens of P. vulgaris was parasitized by the haplosporidian Urosporidium crescens De Turk. This represents a new shrimp host record for this hyperparasite.

Acute toxicity of lead on tolerance, oxygen consumption, ammonia-N excretion, and metal accumulation in Penaeus indicus postlarvae.

The estuaries and backwaters that are the potential breeding grounds of penaeid shrimps are subject to heavy metal pollution through industrial effluents and domestic sewage. In the present investigation, laboratory experiments were conducted to study the acute toxicity of lead on tolerance, oxygen consumption, ammonia-N excretion, and metal accumulation in Penaeus indicus postlarvae. Static bioassay tests were employed to determine tolerance limits. Oxygen consumption, ammonia-N excretion, and metal accumulation were determined in postlarvae by exposing them to different concentrations of lead for a period of 48 h. Oxygen consumption measurements were made by using a respiratory chamber equipped with an oxygen electrode and ammonia-N was determined with trione (dichloro-S-triamine 2,4,6(1H,3H,5H-trione)). Accumulation of metal was estimated by wet-ash method. The LC50 value for 96 h was 7.223 ppm and the regression equation Y=4.1638+0.9738X with correlation coefficient of 0.9613 was obtained by probit method. A decrease in oxygen consumption and ammonia-N excretion was observed in postlarvae with increasing concentration of lead. A concentration-dependent accumulation of metal was noticed in these postlarvae. Modifications in O:N ratios of postlarvae suggest that lead accumulation might have altered utilization patterns.