The distribution of antigen and pathological changes induced by an experimental infection with Aeromonas hydrophila strain KJ99, and its extracellular products, were studied in two species of fish. The microorganism was disseminated systemically and the haemodynamic and tissue changes were similar to those observed in septicaemia of mammals. Intussusception, degeneration and necrosis of the nervous plexus and muscular layers of the gastrointestinal tract were common findings.

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Laboratory bioassays and field trials were carried out to study the effect of metallic copper on the development of Aedes albopictus (Skuse). Multiwire electric cable was used as a source of metallic copper. Three different doses were used in laboratory tests (5, 10, and 20 g/liter) and two in field tests (20 and 40 g/liter). In the laboratory, 10 g/liter induced high mortality and a lack of development in Ae. albopictus larvae and doses of 20 g/liter completely inhibited development. Larval mortality was higher in earlier instars than in third through fourth instars and pupae. No effects were reported on egg hatching. Copper ion concentration in water increased up to 574 ppb for 5 g/liter dose, 710 ppb for 10 g/liter dose, and 1,210 ppb for 20 g/liter dose, within week 6. The increasing concentration of copper in water was correlated positively with the decreasing production of adults. Copper ions concentration < 500 ppb did not or only slightly affected larval development and mortality of Ae. albopictus in laboratory tests. Copper concentrations between 500 and 1,000 ppb delayed larval development and caused high mortality. Copper concentrations > 1,000 ppb inhibited larval development completely killing all the larvae. This last result has been achieved by the use of a 20 g/liter dose of metallic copper in water. Copper also affected adult weight. In field trials, 20 g/liter reduced the number of larvae in treated pots by 90%, and 40 g/liter completely prevented oviposition. Moreover, the persistence of the toxic action of metallic copper in the field lasted for several months.

Abstract. Rickettsial organisms are well-known fish pathogens in both natural and culture environments. This study reports an outbreak of disease in red tilapia larvae caused by piscirickettsia-like organisms (PLOs), which lasted from June until October 2009. Severe mortality was recorded almost exclusively in larvae and postlarvae aged 1-22 days old. Although clinical or gross findings were not evident in diseased fish, histopathology revealed severe necrosis of the epidermis and gill epithelium, with concomitant changes in the underlying skeletal muscle as being the most relevant microscopic lesions. Although PLOs were visible with the routine hematoxylin eosin technique, they were better observed with Giemsa and toluidine blue stains. Transmission electron microscopy revealed that the bacterium was located within the cytoplasm and phagolysosoma-like structures of epithelial cells from the gills and the skin. The bacteria measured 0.9 6 0.2 mm 3 2.1 6 0.6 mm and had a double cell membrane (the outer one having undulating projections), with variable electron-dense and electron-lucent areas. Ultrastructurally, abundant myelin figures surrounded the microorganisms within host cell cytoplasm. Results indicated that Piscirickettsia-like organisms can cause massive epithelial cell damage associated with concomitant alteration of the electrolyte balance.

The use of histopathology in fish sciences is broadly extended, although it is currently devoid of standardization across the literature. There have been initiatives to standardize every step of the histological evaluation, including description, diagnosis, interpretation, data recording and reporting, and statistical analysis, but, in general, the histopathological systems applied to date present a series of limitations that hamper the reproducibility of the derived data. On top of these limitations, an agreed, organ‐by‐organ list of lesions to be recorded is currently lacking. Therefore, this communication proposes a validated and comprehensive list of features to record in skin, head, eye, nervous system, gastrointestinal tract, gonads, kidney, and other organs of farmed red and Nile tilapias (Oreochromis sp. and Oreochromis niloticus L., respectively), white cachama (Piaractus brachypomus), rainbow trout (Oncorhynchus mykiss) and other species. Once this list is agreed and accepted by fish pathologists and other fish scientists, it could be the cornerstone for the development of well‐established and reproducible histopathological scoring systems. This communication highlights the importance of standardization initiatives in fish histology to produce reliable and high‐quality data.