Carlos Azevedo

A fish-infecting myxosporean was found in the urinary bladder of the teleostean Colomesus psittacus, collected from the Amazon River, Brazil. Specimens were sampled in three different periods: May and June, with water temperature ranging from 18–23ºC; August, with water temperature ranging from 24–28ºC; and November and December, with water temperature ranging from 29–32ºC. Upon observation, several fish displayed abnormal behaviour, consisting of erratic movements, and mortality was recorded among them. Necropsy of all sampled fishes revealed hypertrophy of the urinary bladder only among specimens previously displaying the irregular behaviour. Microscopic analysis of this organ confirmed the parasitic infection, resulting in the observation of spores floating free in the urine, and numerous plasmodia attached to the epithelium of the urinary bladder. Light and ultrastructural studies allowed recognition of the spores and plasmodia morphological characteristics. Coelozoic plasmodia were polysporic with varying organizational structure, according to the sampling period. Spores were equilaterally triangular with rounded ends in valvar view, measuring 8.8 ± 0.4 μm (n = 30) in length and 8.4 ± 0.5 μm (n = 30) in width, and displaying a ridge surface pattern. Two polar capsules were observed in the anterior end of the spores, measuring 3.1–3.2 μm in diameter. The spores were morphologically identified as belonging to the recently described genus Triangulamyxa. Further observation and comparison to the morphological features described for Triangulamyxa amazonica, the only other species within this genus, allowed us to conclude our parasite as a new species, herein named Triangulamyxa psittaca sp. nov. from the Amazon River, Brazil. Also, three different stages were distinguished in the plasmodium evolution, based on the observed morphological features at the three sampling periods. Fish sampled during May and June displayed small plasmodia (up to ~ 15–20 μm long), containing early stages of sporogenic development. Fish sampled during November and December presented larger plasmodia (up to ~ 850 μm long), which appeared flattened against and lining the urinary bladder epithelial cells and contained the later stages of sporogenic development, including some mature spores. Fish sampled during August presented plasmodia displaying intermediate morphological features between those observed in infected fish from the other sampling periods. Several immature and mature spores were among the different developmental stages. The parasite-host interface evolution is described throughout the different observed stages, with emphasis on the formation of septate junctions. Considering several previous reports, as well as the different environmental conditions during the sampling periods, the plasmodium development here described appears to be influenced by environmental factors, namely water temperature.

Genus Perkinsus Levine, 1978 (Alveolata, Perkinsidae) an intracellular pathogenic parasite is described from the mantle and gill filaments of a commercially important clam, Meretrix meretrix, collected from the Arabian Gulf, Saudi Arabia. This genus contains currently seven named species: P. marinus, P. olseni (P. atlanticus), P. chesapeaki (P. andrewsi), P. mediterraneus, P. honshuensis, P. beihaiensis and P. qugwadi. Meanwhile, some unnamed Perkinsus sp. have been described in wide variety of mollusc species. Ultrastructural features of Perkinsus sp. trophozites and the host reaction are described. The different developmental stages of trophozoites appeared as single or grouped cells surrounded by amorphous material that constituted cysts or nodules randomly distributed throughout the connective tissue of the mantle. The early trophozoites were generally spherical to ellipsoidal with a circular nucleus containing a prominent central nucleolus. The cytoplasm had several small vacuoles which coalesce to form a great vacuole in the later trophozoites and the nucleus becomes eccentric. Some lomosomes were observed between the wall and the plasmalemma of trophozoites. A large number of degraded and pyknotic cell and several cellular structure with lysed aspects were encountered in the surrounding area near the cysts. Ultrastructural data showed that the lysed granular cells and the coalescence of the granules result in the cyst that encapsulates various trophozoites. In the current study, we describe for the first time the presence of Perkinsus sp. as well as the host reaction in clams from the Saudi Arabian coasts.

Ultrastructural analyses of fish-infecting myxosporean Henneguya piaractus that is found in the gill lamellae of the freshwater teleost Piaractus mesopotamicus (Characidae) and collected from the Paraguai River, Brazil were described. The parasite occurs within large whitish spherical to ellipsoidal polysporic cysts (up to 2.5 mm long) delimited by a layer of fibroblasts generally connected with some capillaries on the gill epithelium. No external morphological signs of disease were visible in the infected fishes. The tailed spores measured 61.5 ± 0.91 (60.2–62.6) μm in total length and ellipsoidal spore body 21.1 ± 0.62 (20.6–21.9) μm long, 6.7 ± 0.40 (6.2–7.3) μm wide and 2.5 ± 0.54 (2.0–3.1) μm thick. The spore wall was about 97 nm of thickness and consisted of a thin electron-dense exospore and a thick electron-lucent endospore with about 85 nm of thickness. The tailed spores were composed of two equal–sized shell valves adhering together along the straight suture line each having in continuity a equal caudal tapering tail measuring 40.5 ± 1.02 (38.7–43.1) μm in length. Two symmetric polar capsules measured 9.8 ± 0.28 (9.3–10.1) μm long and 1.9 ± 0.37 (1.4–2.4) μm wide, each having a polar filament with 10–11 (rarely 12) coils

This study used light and electron microscopy to describe a myxosporean, polysporic, histozoic plasmodium infecting the gill filaments of the freshwater teleost, Semaprochilodus insignis, specimens of which were collected from the Trombetas River (Central Amazonian Region, Brazil). Ultrastructural analyses of the fish-infecting spores identified the parasite as Myxobolus insignis, an organism that occurs within whitish unequal-sized plasmodia located in the intralamellar epithelium of the gill. Based on the observed morphological and ultrastructural features of the plasmodia in this study three stages in the plasmodial evolution were distinguished, related to the sporogonic stages of Myxobolus insignis. The plasmodium walls were also found to constitute a number of layers of fibroblasts, surrounded by collagen fibres, which displayed different morphological arrangements according to the different phases of evolution. This represents the first time such ultrastructural features have been described in detail for Myxobolus insignis plasmodia and offers potentially significant points of comparison with plasmodia from other species of myxosporea.