Factors associated with the prevalence of Perkinsus marinus in Crassostrea virginica from the southern Gulf of Mexico.

The protozoan Perkinsus marinus is considered the most important pathogen of the eastern oyster Crassostrea virginica, causing high mortality in natural and farmed oysters on the Atlantic coast of the US. In Mexico, no serious P. marinus epizootic has been reported. This study describes the current state of P. marinus prevalence in Terminos Lagoon (Mexico) associated with environmental factors including salinity, temperature, ammonium, nitrate, nitrite, silica, and phosphorus. In addition, the association of physiological (hemocyte density, protein concentration) and immunological (lysozyme, agglutination) parameters with the infection were studied. The prevalence was significantly different among seasons with mean values of 70, 23, and 7% in the dry (February to May), rainy (June to September) and north-wind (October to January) seasons, respectively. Only light infection intensity (Mackin scale value < 1) was observed. Prevalence of P. marinus was associated with seasonal salinity, phosphorus, and silica variations. Comparisons of oyster health demonstrates that the rainy and north-wind seasons are stressful periods. Redundancy analysis showed that only 34% of the variation in seasonal P. marinus prevalence was explained by protein concentration (21%), lysozyme (12%), and agglutination (1%). Overall, the data suggest that freshwater input associated with high nutrient concentrations during the rainy and north-wind seasons has a strong negative effect on P. marinus prevalence and also influences the oysters' physiology. It is probable that this seasonal stress was responsible for the absence of an epizootic event in Terminos Lagoon.

Ascocotyle (A.) nunezae n. sp. (Digenea: Heterophyidae) from Yucatan, Mexico.

A new heterophyid species, Ascocotyle (Ascocotyle) nunezae n. sp., is described from adults found in the intestine of naturally infected heron, Casmerodius albus (type host), from the coastal lagoon of Celestún. Yucatan, Mexico, and a domestic chick (Gallus gallus), experimentally infected with metacercariae from Cichlasoma octofasciatum. The new species is characterized mainly by the number (32-37) and arrangement of circumoral spines, which form I complete row of 25-27 circumoral spines and 6-10 accessory spines on the dorsal side, and by the morphology of the ventrogenital sac with a large gonotyl, consisting of 2 indistinctly separated lobes of vesicular tissue. Ascocotyle (A.) nunezae is placed into the nominotypical subgenus Ascocotyle because of the presence of uterine loops at the pharyngeal region and position of vitelline follicles. However, it differs distinctly from other members of this subgenus by the presence of long intestinal ceca reaching posterior to the ventral sucker. Cichlids of the genus Cichlasoma from cenotes, lakes, and the river Río Hondo in the Yucatan Peninsula were natural second intermediate hosts of A. (A.) nunezae, with metacercariae encysted on their gills. Cichlasoma meeki (Brind) was the most heavily infected fish host (total prevalence 75%; mean intensity 11 +/- 9).

Pseudorhabdosynochus yucatanensis sp. n. (Monogenea: Diplectanidae) from the gills of the red grouper Epinephelus morio (Pisces: Serranidae) of the Yucatan Peninsula, Mexico.

Pseudorhabdosynochus yucatanensis sp. n. (Diplectanidae) is described from the gills of the red grouper, Epinephelus morio (Valenciennes, 1824) (Serranidae), from the coast of the Yucatan Peninsula, Mexico. This new species is characterized by having both the ventral and the dorsal squamodiscs composed of 10-12 rows of rods, with 0-1 innermost row forming a closed circle. Furthermore, the vagina of P. yucatanensis has a non-sclerotized ampulla with a fine, sclerotized duct leading to a sclerotized seminal receptacle. Prevalence (percentage of infected fish) and abundance (mean number of worms per examined fish) were estimated for P. yucatanensis from 8 localities along the coast of Yucatan. Prevalence varies from 38% to 100%, while abundance was between 1.2 +/- 0.6 and 43.2 +/- 17.8 worms per fish. The lack of linear relationship between the host length and the number of monogeneans per fish (regression F1,188 = 0.56, p = 0.45) was probably due to the fact that the sample was restricted to juvenile hosts.