Piaractus mesopotamicus é um peixe de água doce encontrado na Bacia Paraná-Paraguai e na região do Pantanal, tendo sido usado em programas de repovoamento no Brasil. Peixes juvenis foram expostos por 96 horas à dose sub-letal de 1.08mg/L do organofosforado (OP) Azodrin®400 que contém 0,43µL/L do principio ativo monocrotofós. A patologia freqüente nas brânquias foi o descolamento epitelial que variou de mínimo nas primeiras 24 horas a severo ou intenso após 48 horas de contaminação. Deformações e degeneração de células pilares nas lamelas respiratórias levando à formação de espaços sanguíneos irregulares e congestão sanguínea, hiperplasia e fusão lamelar também foram observadas. Sugere-se que 48 horas após o T0 é um tempo crítico após exposição a níveis subletais de OP, pois a capacidade de trocas gasosas poderá ter diminuído, levando ao enfraquecimento dos peixes. Os sintomas poderão prejudicar o desenvolvimento dos juvenis introduzidos em corpos de água em programas de repovoamento.

Piaractus mesopotamicus is a freshwater native fish from rivers of the Paraná-Paraguay Basin and of the Pantanal region and has been used for repopulation programs in Brazil. Juvenile fishes were exposed to the sub-lethal dose of 1.08mg/L of the OP Azodrin®400 containing 0.43µL/L of the active principle monocrotophos for 96 h. A frequent pathology in the gills at all times of exposure was epithelial detachment, from minimal until 24 h of exposure, to intense after 48 h of contamination. Deformed pillar cells in the respiratory lamellae leading to irregular blood spaces and blood congestion, as well as hyperplasia and lamellar fusion were observed. These histopathologies suggested that 48 h after T0 was an important time when a reduction in the capability for gaseous exchange with consequent weakening of the fishes' condition could occur. This could impair growth and development of juveniles introduced in water bodies for repopulation programs.

A capacidade de Notothenia rossii Richardson, 1844 detectar presas in diferentes fotoperíodos (24L, 24D e 12L/12D) foi estudada em tanques experimentais. Em 12L/12D houve um maior número de indivíduos estimulados visual e quimicamente enquanto que em 24D a percepção química foi a mesma que a observada em 12L/12D, sendo este ultimo inferior a 24L. A morfologia das estruturas quimio-foto sensoriais, envolvidas na detecção do alimento, foi estudada. As células fotorreceptoras da retina são os cones simples e duplos e os bastonetes. Os botões concentraram-se na região central dos lábios superior e inferior. Seu formato é constante, mas o tamanho é variável. A rosseta olfatória possui um epitélio sensorial e não sensorial rico mucosubstâncias de natureza diversa. Podemos concluir que em diferentes fotoperíodos existe uma diferença de resposta na estimulação visual e química para a detecção de persas e todo o sistema sensorial são mais estimulados em períodos de maior luminosidade, principalmente quando existe uma alternância entre períodos de luz e escuro. Os órgãos sensoriais são complexos quando comparados com outros peixes antárticos como Gobionotothen gibberifrons Lönnberg, 1905 e Ophthalmolycus amberensis Tomo, Marshoff & Torno, 1977) mas similar a Notothenia coriiceps Richardson, 1844.

The influence of photoperiod on the ability of Notothenia rossii Richardson, 1844 to detect prey was studied experimentally. In 12L/12D there was the highest number of individuals stimulated visually and chemically while in 24D chemical perception was the same as that observed in 12L/12D, the latter being lower than in 24L. The ultrastructure of chemo- and photo-sensory structures, involved in the detection of food, was studied. The photoreceptor cells of the retina are single and double cones, and rods. Taste buds were concentrated in the central part of upper and lower lips. Their shape is even, but the size is variable. The olfactory rosette has a sensory and a non-sensory epithelium, being rich in different mucosubstances. The conclusion was that in different photoperiods there is a difference in the response to visual and chemical stimulation for prey detection and that all sensory systems are more stimulated in periods of more luminosity, mainly when there is an alternation between light and dark periods. Sensory organs are complex when compared to some other Antarctic fish such as Gobionotothen gibberifrons Lönnberg, 1905 and Ophthalmolycus amberensis Tomo, Marshoff & Torno, 1977 but similar to those of N. coriiceps Rchardson, 1844.

O peixe antártico Trematoms newnesi (Boulenger, 1902) vive em habitats benticos à pelágicos, em condições fóticas que variam sazonalmente e diariamente, induzindo os movimentos retinomotores. Peixes foram mantidos experimentalmente, durante sete dias, sob luz ou escuro constante, e 12 horas luz/12 horas escuro. O movimento retinomotor do epitélio pigmentar foi estabelecido através do índice de pigmento enquanto que o dos cones foi calculado através do comprimento do mióide. O movimento retinomotor do epitélio pigmentar de T.newnesirevelou que a adaptação à luz constante ocorreu na primeira hora de exposição, permanecendo constante para os próximos sete dias. No entanto, a adaptação para o escuro constante foi mais lenta. A diferença entre a média dos valores dos índices de pigmento nos intervalos de tempo foi significativa nas primeiras quatro horas de exposição ao escuro e somente seis horas após não houve mais diferença significativa entre os tempos. O mióide dos cones alonga-se no escuro e contrai-se no claro. Nos experimentos onde T.newnesi foi submetido a 12 horas luz seguido por 12 horas escuro foi evidenciado que a velocidade e a intensidade dos movimentos retinomotores foi maior quando o animal passa do escuro para a luz do que quando passa da luz para o escuro.

The Antarctic fish Trematomus newnesi (Boulenger, 1902) occurs from benthic to pelagic habitats, in seasonally and daily varied photic conditions that induce retinomotor movements. Fish were experimentally kept under constant darkness or light, and 12Light/12Dark for seven days. The retinomotor movement of the pigment epithelium was established through the pigment index, while that of the cones was calculated as the length of the myoid. The retinomotor movement of the pigment epithelium in T.newnesi,revealed that the adaptation to constant light occurred in the one hour of exposure, remaining constant for the next seven days. However, the adaptation to constant darkness, was slower. The difference between the mean values of the pigment indices in the time intervals of sampling was significant in the first hours of the experiment, and only after six hours they were not significant any more. The myoid of cones became elongated in darkness and contracted in light. In the experiments where T.newnesiwas exposed initially to 12 hours light followed by 12 hours darkness 12 was evidenced that the speed and intensity of the retinomotor movements was higher when darkness changed into light, than when light changed into darkness.

O peixe Antártico Notothenia coriiceps Richardson, 1844 habita meios com variações fóticas diária e anual e as células da retina se adaptam morfologicamente a esta luminosidade ambiental. Dois grupos de peixes foram aclimatados durante sete dias à luz constante ou ao escuro constante. Após secção medular, as retinas foram extraídas e processadas para microscopia de luz e microscopia eletrônica de transmissão. No epitélio pigmentar da retina adaptado sete dias ao escuro, os pigmentos de melanina agregam-se na base coroidal das células epiteliais pigmentares e macrófagos são encontrados no interior do processos apicais entre as células fotorreceptoras. No epitélio adaptado sete dias à luz os pigmentos de melanina se dispõem ao longo das projeções apicais das células epiteliais pigmentares e os macrófagos são ausentes. A região supranuclear dos cones adaptados sete dias à luz possui um citoplasma menos elétron denso devido a presença de canais do retículo endoplasmático que se dilatam aumentando o seu lúmen. As mitocôndrias existentes no segmento interno dos cones adaptados à luz são maiores, e menos elétron densas. As diferenças na morfologia dos cones e nas células epiteliais pigmentares indicam que N. coriiceps possui mecanismos celulares de ajustes na retina provavelmente otimizando a capacidade visual em diferentes situações de luz.

The Antarctic fish Notothenia coriiceps Richardson, 1844 lives in an environment of daily and annual photic variation and retina cells have to adjust morphologically to environmental luminosity. After seven day dark or seven day light acclimation of two groups of fish, retinas were extracted and processed for light and transmission electron microscopy. In seven day dark adapted, retina pigment epithelium melanin granules were aggregated at the basal region of cells, and macrophages were seen adjacent to the apical microvilli, between the photoreceptors. In seven day light adapted epithelium, melanin granules were inside the apical microvilli of epithelial cells and macrophages were absent. The supranuclear region of cones adapted to seven day light had less electron dense cytoplasm, and an endoplasmic reticulum with broad tubules. The mitochondria in the internal segment of cones adapted to seven day light were larger, and less electron dense. The differences in the morphology of cones and pigment epithelial cells indicate that N. coriiceps has retinal structural adjustments presumably optimizing vision in different light conditions.

As brânquias são estruturas vitais para peixes, pois são o principal local de trocas gasosas, assim como parcialmente responsáveis pela osmorregulação, pelo equilíbrio ácido-básico, pela excreção de compostos nitrogenados e pela gustação. Compostos químicos na água podem alterar a morfologia das células branquiais de peixes, que se constituem, dessa forma, em um útil modelo para estudos de impacto ambiental. Visando investigar os efeitos de um composto organofosforado, o metil paration, em brânquias de peixes, exemplares de Metynnis roosevelti foram expostos a doses letais (7ppm) e subletais (1ppm) de Mentox 600 CE. Observações em microscopia óptica e eletrônica de varredura evidenciaram enrugamento do epitélio branquial, seguido por descolamento e hiperplasia. Externamente, os filamentos branquiais apresentaram desaparecimento gradual das microssaliências. Os resultados mostram que, mesmo em doses subletais, o organofosforado poderá levar o animal a sofrer conseqüências secundárias decorrentes das alterações da superfície de trocas gasosas e iônicas.

Gills are vital structures for fish, since they are the main site for gaseous exchange as well as partially responsible for osmorregulation, acid-basic balance, excretion of nitrogenous compounds and taste. Chemicals in the water may alter the morphology of branchial cells of fish that are, therefore, a useful model for environmental impact and ecotoxicology studies. In order to investigate the effects of an organophosphorous compound, methyl parathion, on the gills of the fish, samples of Metynnis roosevelti were exposed to lethal (7ppm) and sublethal (1ppm) doses of Mentox 600 CE. Through light and scanning electron microscopy, shrinking of the branchial epithelium, followed by detachment and hyperplasia were observed. Externally, the branchial filaments presented the gradual disappearance of microridges. Even in sublethal doses, the organophosphorous reduced the health and fitness of these fish, as consequence of secondary effects derived from changes in the branchial epithelium, impairing oxygenation and ionic balance of the organism.

The digestive system of Trichomycterus brasiliensis (Lütken, 1874), a small sized tropical Teleostean fish widely distributed in South America, was studied. Tissue samples were prepared for light and scanning electron microscopy (SEM). Trichomycterus brasiliensis shows stratified esophagus epithelium with taste buds and goblet cells with neutral and acid mucus at the anterior region. The stomach is caecal, presenting a pyloric valve with neutral mucus cells. At the terminal portion it is surrounded by a thick muscular wall. The intestine shows two loops; the epithelium is single columnar, with acid and neutral mucus in goblet cells. Multicellular intestinal glands are absent. Granular cells are often seen in the mucosa, less in the submucosa but were not observed in the muscularis. After the intestine-rectal valve, the rectum shows lower mucosal folds, more goblet cells and a thicker muscularis. No lobes were observed at the liver. Small regions of pancreatic tissue may be identified within the hepatic tissue mainly surrounding vessels and ducts. A compact pancreas may also be observed ventrally to the stomach and covering the bile duct. The possible significance of the heterogeneous character of the digestive tube mucosubstances is discussed. The digestive system of T. brasiliensis presents structural characteristics of a predator fish.

The retina of Metynnis roosevelti Eigenmann, 1915, a very active freshwater fish, was investigated by light and electron microscopy and was found to have a complex neuronal structure that allows rapid responses of visual stimuli. Retina photoreceptors are double cones, single long cones, single short cones and rods. Cone inner segments are arranged as mosaics. The outer nuclear layer contains small nuclei of twin cones, long and wide nuclei of long single cones, spherical large nuclei of short cones, and small dense nuclei of rods. Horizontal, amacrine, bipolar and ganglion neurones are responsible for connections and integration between photoreceptor cells and afferent neurones. The pigmented epithelium comprises a single layer of cylindrical cells each with elongated nuclei, mitochondria at the basal region, and melanin grains that can migrate inside long cell processes, depending on light intensity. In darkness, pigment is concentrated in the basal region of the cells and in daylight it is concentrated in the processes, surrounding and protecting the outer segments of photoreceptors. When exposed experimentally to monochromatic red light, expansion of melanin pigments was provoked at the beginning of light period, followed by their withdrawal after exposure to long wave lengths. No active movements of cones or rods were observed. Considerable renewal of photoreceptor membrane discs occurred after one week in red light, caused by higher level of activation of rods to allow the fish to see in relative darkness. Metynnis roosevelti is a native fish from Brazilian tropical and sub-tropical regions. More recently trials were made to use it in fish cultures in different regions of the countiy. Its capacity to adjust to different photic environments facilitates for rearing in varied environments.

Among the new substances that were synthesised by the chemical industiy during the last decades, with the aim to improve human prosperity, some cause negative effects on non target organisms like fish. Among the pesticides, the organophosphates (OP) are widely used in cattle management, agriculture and aquaculture activities. Brachydanio rerio Hamilton-Buchman, 1822 is used world-wide in fish-tests for the establishment of the lethal levels of pesticides. Nevertheless, these fish show morphological changes in their hepatocytes when exposed experimentally for 24 hours to the sublethal dose of 0.025 µl/l of the OP Dimethoate 500, in acute tests. Right hours after exposure, a high density of cells with cytoplasmic granulation is seen as well as focal necrosis. The main changes that occurred in the first 24 hours of exposure were the loss of the typical polygonal cell shape and of detectable cell limits, lateral migration of nuclei, nuclear size and shape, condensation of chromatin and pycnosis, increased cytoplasmic granulation followed by vacuolisation. After 48 hours in clean water, 72 hours from contamination, besides significant morphological changes and necrosis, focal regeneration of the hepatocytes, canaliculi, ducts and sinusoids were seen. Even having been exposed to the half of the dose considered as safe according to the general pesticide allowance rules, significant changes of the liver tissue were observed.

The behavioural patterns and their cireadian rhythms may be adaptive to the peculiar environmental conditions of subtropical brackish waters where Ba-thygobius soporator Valenciennes, 1837 live. Adult fish were caught at the southern Brazilian coast from mangrove rivers and rocky shores in a bay, where temperature and water salinity vary during the day and through the year. Observation on the behaviour of the animals was undertaken in salinity 8.5ppt, 17.0ppt, 25.5ppt and 34.0ppt, each one in temperatures of 18ºC and 28ºC. Temperature and salinity affect the frequency and intensity of some of the behavioural events, more than its pattern or rhythm. Swimming is rare, decreasing along the day and with temperature increase, being even lower at low salinity; aggressiveness is the highest in the morning being not affected by temperature, but by salinity, being higher the higher it is; territory defence decreases along the day and is lower at high temperature and extreme salinities; fish hide more at high temperature and with the decrease of salinity, but this is not rhythmical; a higher proportion of fish rest in vertical position when salinity and temperature are high, increasing slightly at the beginning of the afternoon; respiratory frequency increases with temperature, salinity and in the afternoon; the colour of the fish is mainly light with spots in all hours of the day and in all temperatures and different levels of salinity, but with a tendency of the presence of some dark fish during the morning and some light ones in the afternoon, showing a higher variability of colours at low temperature and extreme salinities. Besides temperature, salinity and light, feeding seems to be one of the determinant factors for the performance of the typical behaviour of B. soporator.