Microsporidia of Fishes: Characterization of a New Species and Development of the Infectious Focus

Abstract

Fish parasites microsporidia are distributed among fifteen genera. In most cases, the infectious focus present a cyst‐like structure. According to the stage of evolution, the infection focus is either a xenoma or a granuloma. Specific host‐parasite interaction is at the origin of a large diversity of foci form and tissue specificity.In this context, we describe Microgemma tincae n. sp. in the peacock wrasse, Symphodus tinca, fished near the Tunisian coasts. M. tincae is found in the liver of its host. Parasite characterization is based on the ultrastructural description of the life cycle (Transmission Electronic Microscopy) as well as on a part of the rDNA sequence (840 bp of the ssu gene). The inflammatory reaction responsible for the transition from xenoma to granuloma is carefully described. Prevalence is high and small fishes present high level of infection (several foci). One of the parameters responsible for the distribution of the number of foci per fish is the ratio between secondary and new infection.We studied the Spraguea lophii infection to address this question at the molecular level in the angler fish, Lophius spp. We wanted to know if the reaction set up by the host was sufficient to stop the parasite propagation. The analysis was made in two‐dimensional (2D) PFGE at an infection focus scale (1‐mm3 samples). We compared 2D genome images from samples isolated from different parts of one or several infection foci of the same or different fish origin. We conclude that the fish immune system cannot avoid secondary infection.