Parasitism by Monogenoidea in Piaractus mesopotamicus (Characiformes, Characidae) cultivated in Paraná River (Brazil).
This study investigated the occurrence, prevalence, mean abundance and mean intensity of monogenoidean parasites in Piaractus mesopotamicus farmed in cages in the reservoir of the Itaipu Hydroelectric Power Station, Paraná River, Brazil. The parasite distribution pattern and the correlation of prevalence and abundance with the total length of hosts were also investigated. Four monogenoidean species were collected: Anacanthorus penilabiatus, A. toledoensis, Mymarothecium ianwhitingtoni and M. viatorum. All the parasites collected in P. mesopotamicus showed the typical aggregated distribution pattern, and the abundance and the prevalence did not shown any correlation with the total length of hosts.
Community ecology of the metazoan parasites of Banded Croaker, Paralonchurus brasiliensis (Osteichthyes: Sciaenidae), from the coastal zone of the State of Rio de Janeiro, Brazil
Ninety-three specimens of banded croaker, Paralonchurus brasiliensis (Steindachner, 1875), collected from Pedra de Guaratiba (23°01'S, 43°38'W), coastal zone, State of Rio de Janeiro, Brazil, between September 2001 and March 2002, were necropsied to study their infracommunities of metazoan parasites. Fifteen species of metazoan parasites were collected. Paralonchurus brasiliensis is a new host record for 13 parasite species. The majority of fishes were parasitized by one or more metazoan. Larvae of Contracaecum sp. proved to be the dominant species, with highest prevalence and abundance values. The parasite species of P. brasiliensis showed the typical aggregated distribution pattern. Prevalence and abundance of Procamallanus (Spirocamallanus) pereirai was positively correlated with the host total length. Abundance of Contracaecum sp. was positively correlated with the host total length. The abundances of a pair of adult endoparasites (Aponurus laguncula - Procamallanus (S.) pereirai) showed negative covariation and one pair of larvae stages of endoparasites (Nybelinia sp. - Contracaecum sp.) showed positive covariations between their abundances. Paralonchurus brasiliensis showed a metazoan parasite community composed by generalist species, little ordered and with scarce quantitative evidences of interspecific associations. These patterns agree with those detected in preceding studies about the parasite communities of Neotropical sciaenid fishes.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.