Therodamas fluviatilis (Ergasilidae) parasite of Paralichthys orbignyanus (Paralichthyidae): systematics, distribution and histopathology

Author: Ana Luiza Xavier da Silveira Velloso (Currículo Lattes)
Supervisor: Dr Joaber Pereira Junior
Co-supervisor: Dr João Carlos Cousin

Asbtract

The high value of Paralichthys orbignyanus and its tolerance to variations in abiotic factors, point to the potential for cultivation of this sole. This justifies the search for knowledge about its parasitic fauna. Gills of 109 P. orbignyanus from the Lagoa dos Patos estuary and adjacent coast, RS - Brazil, were examined to establish the parasitological indexes of Therodamas fluviatilis, a parasite of the branchial arches. The original description of T. fluviatilis, for Argentina, is the only record available. Drawings and measurements were made of the specimens found, showing no differences with the original description. To determine the distribution of the parasite in the host population, the parasitological indices of prevalence, average intensity of infestation and average abundance were calculated.The hosts were divided by place of collection (sea or lagoon) and in length classes. The indices do not show significant differences in the host length classes or according to the collection site. Complete histological series of parasitized branchial fragments were analyzed to define the pathogenicity of this crustacean. The branchial filaments contiguous to the parasite were metaplastic, with loss of respiratory function. The presence of the copepod and the tissue reaction with strong lymphocytic infiltration put pressure on the tissues and strangulation of the branchial artery wall. The fact that this sole tolerates low salinity and coexists with several species of freshwater fish in the estuary, may explain the presence of T. fluviatilis whose original record was made in Characidae. This is the first record of T.fluviatilis for Brazil and in marine fish and P. orbignyanus is a new host. These findings reinforce the hypothesis that T. fluviatilis is of marine origin. Under cultivation conditions, an increase in infestation intensity is expected and the damage may be even more intense. Therefore, even if P. orbignyanus is tolerant to variations in abiotic factors, under these conditions, attention should be paid to the presence of T. fluviatilis, due to its pathogenicity.

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