Molecular characterization of virulence factors in Aeromonas hydrophila obtained from fish

Multiple factors can be involved in the virulence processes of Aeromonas hydrophila. The objective of the present paper was to verify the presence of aerolysin, hidrolipase, elastase and lipase virulence genes through the polymerase chain reaction (PCR) in A. hydrophila isolates obtained from fish of the São Francisco River Valley, and to evaluate virulence according to the presence of these genes in Nile tilapia fingerlings. One hundred and fourteen isolates from the bacteria were used. DNA was heat extracted and PCR undertaken using specific primers described in the literature. For in vivo tests Nile tilapia fingerlings were used. From the PCR tests, negative isolates for all genes tested were selected, positive isolates for two genes (aerolysin and elastase) and positive for the four genes tested. These were inoculated at a concentration of 10(8) UFC/ml into the tilapias, considered as treatments; another group of animals was used as control (with inoculation of saline solution). In all, 12 distinct standards regarding the presence of virulence factors in isolates from A. hydrophila, were observed. Of the 114 isolates analyzed, 100 (87.72%) presented at least one of the virulence factors under study. The virulence factors were widely distributed among the A. hydrophila isolates. Aerolysin was the most frequent virulence factor present in the isolates analyzed. A. hydrophila led to the mortality of the Nile tilapia fingerlings, regardless of the absence or quantity of virulence genes tested.

Efeito do eugenol como agente mitigador do estresse no transporte de juvenis de tilápia do Nilo

RESUMO O Brasil se destaca no cenário americano como um dos países com maior potencial para a piscicultura, principalmente a dulcícola. A tilápia do Nilo (Oreochromis niloticus) se destaca sendo a espécie mais cultivada em nosso país. Metodologias para diminuir a interferência de agentes estressores nas funções vitais e fisiológicas dos peixes são importantes durante o manejo. O presente trabalho teve como objetivo avaliar o efeito do eugenol nas respostas metabólicas e iônicas de juvenis de tilápia do Nilo, submetidos ao transporte em sacos plásticos, em diferentes densidades, a fim de verificar a eficiência do produto como agente mitigador do estresse. O eugenol foi utilizado na concentração de 15mg/L em água. As densidades avaliadas foram 4, 7 e 10 peixes L-1, equivalente a 140, 245 e 350g L-1. Após quatro horas de transporte foram avaliados os parâmetros metabólicos (glicose e lactato) e iônicos (cloreto, magnésio e cálcio), bem como a qualidade da água nos sacos plásticos. Em relação aos dois parâmetros metabólicos, o uso do eugenol com o intuito de diminuir as respostas do estresse não foi satisfatório. Houve elevação no nível de glicose nas densidades 140 e 350g L-1 imediatamente ao término do transporte, e o teor de lactato dos peixes na densidade 245g L-1 aumentou 24 horas depois, indicando que os animais não conseguiram manter a homeostase inicial. Dentre as concentrações de íons avaliados, o magnésio foi o que sofreu maior variação. Podemos concluir que a adição de 15mg L-1 de eugenol na água durante o transporte de juvenis de tilápia do Nilo nas densidades de 140, 245 e 350g L-1 não foi capaz de minimizar as respostas ao estresse.

Environmental blue light prevents stress in the fish Nile tilapia

The present study aimed to test the effects of blue, green or white light on the stress response of the Nile tilapia, Oreochromis niloticus (L.). Each color was tested on two groups of isolated adult Nile tilapia (8 replicates each): one being subjected to confinement stress, and the other not (control). A different environmental color was imposed on each compartment by covering the light source with cellophane of the respective color (green or blue; no cellophane was used for white light). The intensity of green, white and blue lights was 250, 590 and 250 lux, respectively. Basal plasma cortisol levels were determined for each fish prior to the experimental procedures. The fish were confined by being displaced toward one side of the aquarium using an opaque partition for 1 h both in the morning and the afternoon of the two consecutive days of the test. At the end of this 48-h period, plasma cortisol levels were measured again. Basal cortisol levels (ng/ml) were similar for each group (ANOVA, F(2;42) = 0.77, P = 0.47). Thus, plasma cortisol levels were analyzed in terms of variation from their respective basal level. After confinement, plasma cortisol levels were not increased in fish submitted to a blue light environment. Thus, blue light prevents the confinement-induced cortisol response, an effect not necessarily related to light intensity.

Sex-specific compensatory growth in food-deprived Nile tilapia

Female Nile tilapia incubate fertilized eggs in their mouth until they are released as alevins. Consequently, the female may not eat during this period. Thus, it would be expected that female Nile tilapia are more adapted to recovering from fasting than males, which do not display this behavior. To test this hypothesis we conducted an experiment with two groups of fish consisting of 7 males and 7 females each, with one fish per aquarium. The experiment was divided into three phases involving adjustment of the animals to experimental aquaria (0-15th day), fasting (16th-27th day), and refeeding (27th-42nd day). Compensatory growth performance was assessed by specific growth rate, weight, food conversion efficiency and food intake. Food conversion efficiency increased after fasting with a similar rate for both sexes. However, specific growth rate, food intake and weight gain (%) were significantly higher in males than in females in the refeeding phase. Thus, we conclude that male Nile tilapia can compensate for a fasting period more efficiently than females, refuting our hypothesis. A possible mechanism involved in the greater male compensation is that they presented greater hyperphagia than females, concomitantly with a similar rate of food conversion efficiency for both sexes during refeeding, which would probably be provoking greater growth in males.

Eye color as an indicator of social rank in the fish Nile tilapia

We investigated the association of eye color with the dominant-subordinate relationship in the fish Nile tilapia, Oreochromis niloticus. Eye color pattern was also examined in relation to the intensity of attacks. We paired 20 size-matched fish (intruder: 73.69 ± 11.49 g; resident: 75.42 ± 8.83 g) and evaluated eye color and fights. These fish were isolated in individual aquaria for 10 days and then their eye color was measured 5 min before pairing (basal values). Twenty minutes after pairing, eye color and fights were quantified for 10 min. Clear establishment of social hierarchy was observed in 7 of 10 pairs of fish. Number of attacks ranged from 1 to 168 among pairs. The quartile was calculated for these data and the pairs were then divided into two classes: low-attack (1 to 111 attacks - 2 lower quartiles) or high-attack (112 to 168 attacks - 2 higher quartiles). Dominance decreased the eye-darkening patterns of the fish after pairing, while subordinance increased darkening compared to dominance. Subordinate fish in low-attack confrontations presented a darker eye compared to dominant fish and to the basal condition. We also observed a paler eye pattern in dominants that shared low-attack interactions after pairing compared to the subordinates and within the group. However, we found no differences in the darkening pattern between dominants and subordinates from the high-attack groups. We conclude that eye color is associated with social rank in this species. Moreover, the association between eye color and social rank in the low-attack pairs may function to reduce aggression.

Persistent organic pollutants in sediments and fish from Lake Victoria, Uganda

This thesis describes the occurrence and sources of selected persistent organic pollutants (POPs) such as polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and hexachlorocyclohexanes (HCHs) in the northern watershed of Lake Victoria. Sediments and fish were collected from three highly polluted embayments (i.e. Murchison Bay, Napoleon Gulf and Thurston Bay) of the lake. The analysis for PCDD/Fs, PCBs and PBDEs was done using a high resolution mass spectrometer coupled to a gas chromatograph (GC), and a GC equipped with an electron capture detector was used for HCHs. Total (Σ) PCDD/Fs, PCBs and PBDEs in sediments ranged from 3.19 to 478, 313 to 4325 and 60.8 to 179 pg g-1 dry weight (dw), respectively. The highest concentrations of pollutants were found at sites close to industrial areas and wastewater discharge points. The maximum concentrations of PCDD/Fs, PCBs, PBDEs and HCHs in fish muscle homogenates were 49, 779, 495 and 45,900 pg g-1 wet weight (ww), respectively. The concentrations of the pollutants in Nile perch (Lates niloticus) were significantly greater than those in Nile tilapia (Oreochromis niloticus), possibly due to differences in trophic level and dietary feeding habits among fish species. World Health Organization-toxic equivalency quotient (WHO2005-TEQ) values in the sediments were up to 4.24 pg g-1 dw for PCDD/Fs and 0.55 pg TEQ g-1 dw for the 12 dioxin-like PCBs (dl-PCBs). 23.1% of the samples from the Napoleon Gulf were above the interim sediment quality guideline value of 0.85 pg WHO-TEQ g-1 dw set by the Canadian Council for Ministers of the Environment. The WHO2005-TEQs in fish were 0.001-0.16 pg g-1 for PCDD/Fs and 0.001-0.31 pg g-1 ww for dl- PCBs. The TEQ values were within a permissible level of 3.5 pg g−1 ww recommended by the European Commission. Based on the Commission set TEQs and minimum risk level criteria formulated by the Agency for Toxic Substances and Disease Registry, the consumption of fish from Lake Victoria gives no indication of health risks associated to PCDD/Fs and PCBs. Principal component analysis (PCA) indicated that anthropogenic activities such as agricultural straw open burning, medical waste incinerators and municipal solid waste combustors were the major sources of PCDD/Fs in the watershed of Lake Victoria. The ratios of α-/γ-HCH varied from 0.89 to 1.68 suggesting that the highest HCH residues mainly came from earlier usage and fresh γ-HCH (lindane). In the present study, the concentration of POPs in fish were not significantly related to those in sediments, and the biota sediment accumulation factor (BSAF) concept was found to be a poor predictor of the bioavailability and bioaccumulation of environmental pollutants.

Environmental color affects Nile tilapia reproduction

We investigated the effects of environmental color on the reproductive behavior of Nile tilapia, Oreochromis niloticus. Two environmental colors were tested by covering the aquarium (60 x 60 x 40 cm) with white (12 groups) or blue (13 groups) cellophane and observing reproductive behavior in groups of 2 males (10.27 ± 0.45 cm) and 3 females (10.78 ± 0.45 cm) each. After assignment to the respective environmental color (similar luminosity = 100 to 120 Lux), the animals were observed until reproduction (identified by eggs in the female's mouth) or up to 10 days after the first nest building. Photoperiod was from 6:00 h to 18:00 h every day. Food was offered in excess once a day and water quality was similar among aquaria. Daily observations were made at 8:00, 11:00, 14:00 and 17:00 h regarding: a) latency to the first nest, b) number of nests, c) gravel weight removed (the male excavates the nest in the bottom of the aquarium), d) nest area, and e) mouthbrooding incubation (indication of reproduction). The proportion of reproducing fish was significantly higher (6 of 13) in the group exposed to the blue color compared the group exposed to the white color (1 of 12; Goodman's test of proportions). Moreover, males under blue light removed significantly larger masses of gravel (blue = 310.70 ± 343.50 g > white = 130.38 ± 102.70 g; P = 0.01) and constructed wider nests (blue = 207.93 ± 207.80 cm² > white = 97.68 ± 70.64 cm²; P = 0.03) than the control (white). The other parameters did not differ significantly between light conditions. We concluded that reproduction in the presence of blue light was more frequent and intense than in the presence of white light.

Stress responses of the fish Nile tilapia subjected to electroshock and social stressors

Plasma cortisol and glucose levels were measured in 36 adult Nile tilapia males, Oreochromis niloticus (standard length, mean ± SD, 14.38 ± 1.31 cm), subjected to electroshock and social stressors. Pre-stressor levels were determined 5 days after the adjustment of the fish to the experimental aquaria (1 fish/aquarium). Five days later, the effects of stressors on both cortisol and glucose levels were assessed. The following stressors were imposed for 60 min: pairing with a larger resident animal (social stressor), or a gentle electroshock (AC, 20 V, 15 mA, 100 Hz for 1 min every 4 min). Each stressor was tested in two independent groups, one in which stress was quantified immediately after the end of the 60-min stressor imposition (T60) and the other in which stress was quantified 30 min later (T90). Pre-stressor values for cortisol and glucose were not statistically different between groups. Plasma cortisol levels increased significantly and were of similar magnitude for both electroshock and the social stressor (mean ± SD for basal and final samples were: electroshock T60 = 65.47 ± 15.3, 177.0 ± 30.3; T90 = 54.8 ± 16.0, 196.2 ± 57.8; social stress T60 = 47.1 ± 9.0, 187.6 ± 61.7; T90 = 41.6 ± 8.1, 112.3 ± 26.8, respectively). Plasma glucose levels increased significantly for electroshock at both time points (T60 and T90), but only at T90 for the social stressor. Initial and final mean (± SD) values are: electroshock T60 = 52.5 ± 9.2, 115.0 ± 15.7; T90 = 35.5 ± 1.1, 146.3 ± 13.3; social stress T60 = 54.8 ± 8.8, 84.4 ± 15.0; T90 = 34.5 ± 5.6, 116.3 ± 13.6, respectively. Therefore, electroshock induced an increase in glucose more rapidly than did the social stressor. Furthermore, a significant positive correlation between cortisol and glucose was detected only at T90 for the social stressor. These results indicate that a fish species responds differently to different stressors, thus suggesting specificity of fish stress response to a stressor.

Níveis de mercúrio total em peixes de água doce de pisciculturas paulistas

Avaliou-se os níveis de mercúrio total em amostras de peixes de água doce, procedentes de pesqueiros e pisciculturas de 39 regiões do estado de São Paulo. As espécies de peixes estudadas foram: pacu (Piaractus mesopotamicus), tilápia (Oreochromis niloticus), piauçu (Leoporinum sp), matrinxã (Brycon cephalus), tambaqui (Colossoma macropomum) e carpa (Cyprinus carpis). Foram avaliadas três metodologias de digestão de amostras para a determinação de mercúrio total, variando-se o volume de mistura sulfonítrica utilizada e a concentração do permanganato de potássio, sendo que o uso de 10mL de mistura sulfonítrica e solução de permanganato de potássio a 7% (m/v) na digestão da amostra foi a que forneceu as recuperações mais altas (96%), precisão de 1% e limite de quantificação de 0,3µg/kg. Após a validação do método, foram realizadas as determinações de teor de mercúrio total em 293 amostras de pescado, usando a técnica de espectrometria de emissão com fonte de plasma acoplado em gerador de hidretos. Os níveis médios de mercúrio encontrados variaram entre: tambaqui (0,0003-0,012mg/kg), carpa (0,063mg/kg), matrinxã (0,0003-0,074mg/kg), pacu (0,0003-0,078mg/kg), piauçu (0,0003-0,183mg/kg) e tilápia (0,0003-0,217mg/kg). Os resultados mostraram que nenhuma das amostras procedentes das diferentes regiões e diferentes pesque-pagues, apresentaram níveis de mercúrio total acima do permitido pela legislação brasileira, que é de 0,5mg/kg para pescado não-predador.

Bacterial ecology of tilapia fresh fillets and some factors that can influence their microbial quality

The purpose of research was to investigate the bacterial ecology of tilapia (Oreochromis niloticus) fresh fillets and some factors that can influence its microbial quality. Samples of fish cultivation water (n = 20), tilapia tegument and gut (n = 20) and fresh fillets (n = 20) were collected in an experimental tilapia aquaculture located in the city of Lavras, Minas Gerais, Brazil. Staphylococcus spp., Aeromonas spp., Enterococcus spp. and Enterobacteriaceae were quantified using selective plating. For the enumeration of Pseudomonas spp., the most probable number technique (MPN) was utilized. Bacterial colonies (n = 198) were identified by Gram strain and biochemical tests. Aeromonas spp., Pseudomonas spp., Enterococcus spp. and Enterobacteriaceae were found in the cultivation water (water from a fishpond cultivation), tegument, gut, and fresh fillets. Staphylococcus spp. was not isolated in the cultivation water. Salmonella spp. was not detected. The count variable of 10 to 10³ CFU or MPN.(g or mL)-1. Associated to freshwater tilapia fillet processing, there is a large variety of microorganisms related to foodborne illnesses and fish products deterioration.

Teor de colesterol e composição centesimal de algumas espécies de peixes do estado do Ceará

O presente estudo tem como objetivo determinar o teor de colesterol total em amostras de pescado de água marinha e doce. As amostras analisadas foram o pargo marinho, Lutjanus purpureus, e os seguintes peixes de água doce: tilápia do Nilo, Oreochromis niloticus, curimatã, Prochilodus cearensis e a sardinha, Triportheus angulatus, adquiridas em pontos comerciais (frigoríficos, feira de pescado da praia de Mucuripe e feira-livre suburbana) de Fortaleza - Ceará. Além da determinação do teor de colesterol, também foram avaliados a composição química centesimal e o valor calórico das amostras. O teor médio de colesterol (mg.100 g-1) apresentado foi 33,5 para o pargo, 28,4 para a tilápia, 93,8 para o curimatã e 61,2 para a sardinha. Em relação à composição centesimal, os seguintes teores médios foram obtidos, respectivamente, para pargo, tilápia, curimatã e sardinha: 80,7; 80,2; 76,4 e 77,2% de umidade; 18,4; 17,7; 18,7 e 17,6% de proteína total; 1,0; 1,2; 3,2 e 4,6% de lipídio total; 0,7; 0,8; 0,8 e 1,0% de cinza, e 0,5; 0,6; 2,0 e 0,3% de carboidratos. O valor energético médio (kcal.100 g-1) foi de 83,6 para o pargo, 83,7 para a tilápia, 108,4 para o curimatã e de 111,8 para a sardinha.

Physicochemical and sensory characteristics of snack made with minced Nile tilapia

Nile tilapia is one of the major fish species cultivated worldwide and in Brazil. The tilapia fillet yield is between 30-35%, thus around 70% of waste is generated. A portion of this waste can be used to obtain minced fish, and the resulting product can be used as meat raw material to prepare fish snacks. The aim of this study was to produce fish snacks containing different inclusion levels (20, 30, and 40%) of minced fish obtained from Nile tilapia processing waste and evaluate their physicochemical characteristics and sensory acceptance. Protein content, ash, water activity, and hardness increased with increasing inclusion of minced fish. The scores obtained in the sensory evaluation were: flavor acceptance (from 7.2 to 5.7), texture (from 7.4 to 5.3), overall acceptance (from 7.1 to 5.9), and willingness to purchase (from 4.0 to 3.1). This study demonstrates that the inclusion of 20 to 40% of minced fish of Nile tilapia in snacks is well accepted and improves their nutritional value without affecting the physicochemical properties.

Fresh pasta enrichment with protein concentrate of tilapia: nutritional and sensory characteristics

Abstract With the goal of developing and characterizing the nutritional and sensory aspects of fresh pasta supplemented with tilapia protein concentrate, four types of pasta were prepared, with inclusion of 0, 10, 20, or 30% of tilapia protein concentrate. Linear effects were observed (P < 0.01) in crude protein, total lipids, ash, carbohydrate, and caloric values; these parameters increased with increasing amounts of tilapia protein concentrate in the pasta. The concentration of Na, P, Ca, Mg, and Zn increased linearly (P < 0.01) in correlation with the increase in protein concentrate content, while Fe content decreased linearly (P < 0.01). In the sensory analysis, texture, overall impression, and the acceptance index demonstrated a cubic regression (P < 0.05), with the inclusion of 20% protein concentrate yielding the best scores. Including up to 30% of tilapia protein concentrate in pasta yields an increased nutritional value, but based on the sensory results, 20% of tilapia protein concentrate in pasta is the recommended maximum level.

Avaliação da biocompatibilidade e da propriedade bactericida de nanotubos de dióxido de titânio impregnados com lectina e nanopartículas de prata para aplicações biomédicas

O titânio e suas ligas são os materiais mais comumente utilizados na substituição de tecidos duros por possuírem resistência mecânica, biocompatibilidade, resistência à corrosão e fácil manipulação. Embora o titânio possua várias vantagens sobre outros biomateriais, seu uso em longo prazo pode ocasionar problemas de rejeição. A modificação da superfície do titânio a fim de criar microrrugosidades é uma estratégia efetiva para melhorar a adesão e proliferação celular sobre implantes. Quando um implante danifica ou invade as barreiras epitelial e das mucosas, pode servir como reservatório para microrganismos e desta forma predispor à infecção. Neste sentido, o objetivo deste trabalho foi modificar a superfície do titânio, utilizando nanopartículas de prata (Ag) e lectina, a fim de melhorar a sua biocompatibilidade e conferir propriedades antimicrobianas a este material. O racional por trás destas mudanças é que a criação de uma topografia em nanoescala pode contribuir para mimetizar o ambiente celular melhorando a osseointegração e diminuindo o risco de infecção. Em nosso estudo, nanotubos de dióxido de titânio (NTs-TiO2) com estrutura bem distribuída e organizada, com diâmetro em torno de 70–80nm, foram sintetizados por anodização eletroquímica e decorados com nanopartículas de Ag usando a técnica de layer-by-layer (LbL), enquanto a lectina do peixe Oreochromis niloticus (OniL) foi incorporada aos NTs-TiO2 por spin coating. Estas amostras foram caracterizadas e avaliadas quanto a sua citotoxidade, adesão celular, potencial osteogênico e atividade bactericida. Nossos resultados mostraram que tanto as nanopartículas de Ag, como a Onil foram incorporadas com sucesso à superfície dos NTs-TiO2. Entretanto nossas preparações de LbL não foram capazes de melhorar a biocompatibilidade ou inibir o crescimento de bactérias nos NTs-TiO2. Por outro lado, a funcionalização dos NTs-TiO2 com a OniL induziu eficientemente a adesão e proliferação dos osteoblastos. Nossos resultados apontam para o uso da lectina OniL para melhorar a qualidade dos implantes de NT-TiO2 existentes.

Avaliação de metais na água, no sedimento e nos peixes da lagoa Azul, formada por lavra de mineração de carvão a céu aberto, Siderópolis-SC

Entre maio de 2001 e janeiro de 2002, foram realizadas coletas sazonais na lagoa Azul, Siderópolis, SC. Esta lagoa formou-se por lavra de mineração de carvão a céu aberto desativada. Foram avaliadas as concentrações de Cr, Mn, Ni, Zn e Fe na água e no sedimento. Estes metais, exceto o Fe, foram também analisados no músculo e no fígado das espécies dos peixes Oreochromis niloticus (tilápia) e Geophagus brasiliensis (acará). O objetivo foi avaliar a qualidade da lagoa, bem como, das espécies de peixes predominantes, devido a preocupação quanto ao consumo potencial das mesmas pela população do entorno. As análises do sedimento, quando comparada a locais não contaminados, indicam concentração elevada para Fe, Mn, Cr e Zn. No compartimento água as concentrações de Fe, Mn e Ni estão acima do estabelecido para a classe 2 da Resolução CONAMA 20/86. Conforme análise estatística, em ambos os compartimentos abióticos ocorrem diferenças significativas entre os 4 pontos amostrados, porém diferença sazonal ocorre somente para o compartimento água. O conteúdo de metais em peixes não apresenta diferença significativa entre as espécies analisadas, todavia entre os diferentes tecidos analisados, o fígado apresentou a maior concentração em ambas as espécies. Através das análises do músculo (parte comestível), foi possível avaliar o risco à saúde humana. Segundo a estimativa da ingestão diária, os peixes analisados não propiciam risco aparente de contaminação à população do entorno, conforme os critérios adotados para o teor dos metais avaliados.