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Histology of gill, liver and kidney in juvenile fish Colossoma macropomum exposed to three temperatures. Water temperature is an important factor that affects growth and antioxidant enzyme activities in fish, and when adverse, it may trigger diseases in fish populations. C. macropomum is a freshwater neotropical fish widely distributed in South America and abundant in river basins as the Amazon and Orinoco. It is highly used for intensive aquaculture development and is a very important product for the local riverside economy in Venezuela. The purpose of our study was to examine the water temperature effect on gills, liver and kidneys of juvenile fishes of C. macropomum. Eighteen juveniles with biometrical index of 17.87±7.88cm and 87.69±34.23g were respectively exposed to three culture temperatures (T18, T29 and T35ºC) during a period of 21 days. Histological analyses on gills, liver and kidney were made according to standard methodologies. Our results showed that these tissues exhibited normal citoarchitecture at T29. On the contrary, T18-gills displayed brachiallipid droplets inside brachial epithelium; and disorganization in the brachial tissue was observed at T35. Furthermore, we observed two kinds of hepatocytes (dark and light) on T18°C-liver. The T35-liver samples showed cytoplasmatic granulation and damages in cytoplasmatic membrane. Kidney samples from T18 observed alterations in the cellular distribution of the hematopoietic tissue; while, at T35, the most important feature observed was the disorganization of the glomerular structure. We concluded that T18 and T35 are respectively critical and severe temperatures to C. macropomum; besides, the most sensible tissues to changes induced by temperature in this species were the liver and gills. Rev. Biol. Trop. 61 (2): 797-806. Epub 2013 June 01.

Abstract. Metal content, Metallotionein and physiological condition (RNA/DNA ratio) were analyzed in Cachama, Colossoma macropomum from the Orinoco River. Juvenile samples were dissected and one gram of white muscle gills, kidney and liver was taken. Cu, Cd, Pb, Ni and Fe were analyzed by atomic absorption spectrophotometer using TORT and LUTSI as reference material. Metallothioneins were determined with Ellman´s reagent and RNA/DNA ratio was analyzed by fluorometric method. Results showed that Cd, Cu, Ni, Fe, and Pb levels were significantly higher in liver than muscle. There was no difference statistically between Mts concentrations in liver, kidney and gills; muscle showed the lowest Mts concentrations. Multivariate analysis ACP determined relationship between Mts-L and Cu and Mts-G and Cd. The Mts in muscle was related with Pb and Cd. There was no association between physiological condition and metals concentrations, however, the RNA/ DNA showed relationship with Mts-M and Mts-L