Wallinia mexicana sp. n. is described from the Mexican tetra, Astyanax mexicanus (De Filippi) (Characidae Weitzman), from two localities in northern Mexico. The new species can be distinguished from the two congeneric species, described from small-bodied characids in South and Central America, mainly by the posterior extent of the vitelline follicles (halfway between the posterior testis and the end of the caeca), by having a larger oesophagus, testes that are always oblique, and eye-spot remnants. The distinct status of the new species was confirmed by molecular data (28S rRNA gene sequences). Phylogenetic analysis suggests the new species is the sister species of W. chavarriae Choudhury, Hartvigsen et Brooks, 2002 described from characids in northwestern Costa Rica. Additionally, genetic divergence between these congeners reached 3.3%, a value higher than that observed for closely related species pairs of allocreadiids for that molecular marker. Based on these new findings, recently published records of this new species as Magnivitellinum simplex Kloss, 1966 and Creptotrematina aguirrepequenoi Jiménez-Guzmán, 1973 in Astyanax mexicanus from Durango and San Luis Potosi states, respectively, are corrected., Gerardo Pérez-Ponce de León, Ulises Razo-Mendivil, Berenit Mendoza-Garfias, Miguel Rubio-Godoy, Anindo Choudhury., and Obsahuje bibliografii
Microhabitat preference of the monogenean Discocotyle sagittata (Leuckart, 1842) was determined in late spring and late autumn in rainbow trout, Oncorhynchus mykiss (Walbaum), reared in the Isle of Man, UK. Discocotyle sagittata exhibits a preference for attachment to anterior gill arches: 29% of all worms occurred on gill arch I, 28% on II, 25% on III and 18% on IV. This distribution pattern on the introduced salmonid species is the same as reported for its native European host, the brown trout Salmo trutta (L.). Previous experimental work suggested that invasion is a passive process followed by post-invasion migration to anterior gill arches; the present work provides evidence of equivalent site selection taking place in fishes maintained under conditions promoting continuous reinfection in aquaculture. Migration may be density-dependent, since a significant inverse association was found between the intensity of mature parasites and their proportion on anteriormost gill arch I.
Experimental infection of rainbow trout Oncorhynchus mykiss (Walbaum) with the monogenean Discocotyle sagittata (Leuckart, 1842) allowed comparison between trickle and single exposure, two infection modes demonstrated to occur in the wild. Both types of infection resulted in mean larval attachment success around 50%, which was significantly dependent on dose of infective larvae used (P < 0.0001), but was not affected by mode of infection (P = 0.244). Worms recovered from fish exposed to the same number of oncomiracidia but different mode of infection differed in their rate of development. The developmental stage attained by parasites was significantly affected by number of infective larvae used (P = 0.005), and by the interaction between dose and mode of infection (P = 0.026), suggesting competition among attached larvae. Statistical analysis demonstrated that in the early stages of infestation, worm distribution over the gill arches can be explained by the relative amount of water flowing over them. One, two and three months post-infection parasite numbers were comparable (P = 0.805), but their observed distribution gradually decreased in gill arches III and IV and increased in gill arch I, suggesting that parasites migrate after initial attachment. These results reproduce phenomena observed in the field, indicating that the experimental infection system could be employed to study infection dynamics and host-parasite interactions under controlled conditions.