Behaviour of personality-screened juvenile Oreochromis niloticus in different challenges: Bold fish present more exploratory capacity and learning to face imposed challenges.

The investigation of cultivation and management techniques that take into account behaviour and animal welfare becomes important due to their direct relationship with animal performance. This study aimed to classify juvenile Oreochromis niloticus by personality and compare their performance at exploration and competition tasks. The new object test was used to select bold and shy animals, which were then tested to see which first approached an object. The food competition test involved placing three feed pellets inside a cylinder and measuring the time taken until the pellet was eaten. The new object test found bold animals with a shorter mean time to approach the object than shy animals approaching 65% of the first object when compared to shy. The food competition test found that the bold animals ingested the first pellet more times and with a shorter average time of ingestion than shy animals, no difference in the second intake, whereas the results for the third were same as those for the first. Shy animals had higher intake of the second pellet. Bold animals explored their environment faster in both challenges, while shy individuals exhibited ability to learn from the challenges imposed in the study.

Involvement of the phosphoryl transfer network in gill bioenergetic imbalance of pacamã (Lophiosilurus alexandri) subjected to hypoxia: notable participation of creatine kinase.

Hypoxia is among the most critical environmental stressors for fish in aquatic environments, and several energetic alterations have been associated with it. The aim of the present study was to evaluate the involvement of the phosphoryl transfer network and its effects on adenosine triphosphate (ATP)-dependent enzymes during hypoxia, as well as the role of oxidative stress in the activity of the phosphoryl transfer network in pacamã (Lophiosilurus alexandri) subjected to severe hypoxia. Branchial creatine kinase (CK; cytosolic and mitochondrial fractions), adenylate kinase (AK), and pyruvate kinase (PK) activities were inhibited after 72 h of exposure to hypoxia compared to their respective normoxia groups, and remained low (except for AK) after 24 and 72 h of re-oxygenation. Activities of the branchial sodium-potassium pump (Na+, K+-ATPase) and proton pump (H+-ATPase) were inhibited in fish exposed to 72 h of hypoxia compared to the normoxia group, remained inhibited after 24 h of re-oxygenation, and were restored to physiological levels after 72 h of re-oxygenation. Levels of branchial reactive oxygen species (ROS) were higher in fish exposed to hypoxia for 72 h compared to the normoxia group, and increased during re-oxygenation. Lipid peroxidation (LOOH) levels were higher in fish subjected to 72 h of hypoxia compared to the normoxia group, and remained higher during re-oxygenation. On the other hand, protein sulfhydryl (PSH) levels were lower in fish exposed to hypoxia for 72 h compared to the normoxia group, and remained low during re-oxygenation. Based on this evidence, inhibition of the activities of enzymes belonging to phosphoryl transfer network contributed to impairing energetic homeostasis linked to ATP production and ATP utilization in gills of pacamã subjected to hypoxia, and remained inhibited during re-oxygenation (except AK activity). Moreover, inhibition of the phosphoryl transfer network impaired activity of ATP-dependent enzymes, which can be mediated by ROS overproduction, lipid peroxidation, and oxidation of SH groups.

An external tag for fish: tagging effects in different fish size classes and its influence on growth performance and hematology of Lophiosilurus alexandri (Siluriformes: Pseudopimelodidae)

This study tested an external tag for juveniles of Lophiosilurus alexandri and measured the effects of tagging in different size classes of fishes. Experiment 1 evaluated the retention rate and influence of the tag on survival and growth of three hundred fishes divided Small, Medium and Large size classes. After 90 days of experiment the fishes had 100% survival and the tag had a higher retention rate for animals of the Large size class. Experiment 2 evaluated the tag's influence on hematology parameters of forty-two fishes at 5, 10 and 30 days post-tagging. In this experiment both tagged and untagged animals experienced 9.4% mortality. The hematocrit was higher on the 30th day for tagged animals than for untagged animals. No difference was observed for leukocytes, plasma protein, erythrocytes and mean corpuscular volume. It was concluded from Experiment 1 that the tag reduced growth performance when applied to small sized juvenile L. alexandri, and that the tag retention rate increased with increasing animal size. Among the hematological parameters studied for juveniles on the Experiment 2 the tag only influenced the hematocrit parameters, which shows that the tag can be used without considerable influence on the hematological parameters of juvenile L. alexandri.(AU)

Esse estudo testou a utilização de marcadores externos em juvenis de Lophiosilurus alexandri, assim como o tamanho mínimo ideal do peixe para marcação. No experimento 1 foi avaliado a taxa de retenção e a influência do marcador sobre a sobrevivência e crescimento dos peixes divididos por tamanho nas classes: Pequeno, Médio e Grande. Após 90 dias, os peixes apresentaram 100% de sobrevivência e uma taxa de retenção mais elevada para os animais classificados como grandes. O segundo experimento avaliou a influência do marcador sobre os parâmetros hematológicos dos animais após 5, 10 e 30 dias da marcação. Neste experimento, foram observados valores mais elevados para o hematócrito no 30º dia para os animais marcados, enquanto nenhuma diferença foi observada para leucócitos, proteína plasmática, eritrócitos e volume corpuscular médio. Concluiu-se o que o marcador reduziu a taxa de crescimento dos animais menores, e que a taxa de retenção aumentou com o aumento do tamanho do animal. Dos parâmetros hematológicos avaliados, o marcador influenciou apenas no valor do hematócrito, o que mostra que o marcador pode ser usado sem considerável influência nos parâmetros hematológicos do L. alexandri.(AU)

Comparative study of the chemical composition, fatty acid profile, and nutritional quality of Lophiosilurus alexandri (Siluriformes: Pseudopimelodidae), a Brazilian carnivorous freshwater fish, grown in lotic, lentic, and aquaculture environments

Lophiosilurus alexandri is a carnivorous freshwater fish endemic of São Francisco basin and an endangered species. In this study, we analysed the chemical composition (moisture, protein, ash and lipid), fatty acid profile, and nutritional quality (atherogenic index, thrombogenecity index, ratio between hypocholesterolemic and hypercholesterolemic fatty acids and ω6/ω3 = ratio) of L. alexandri in lotic (river), lentic (hydroelectric dams) environments, under natural fed, and in laboratory controlled conditions fed with commercial diets. Cultured and lentic fish had significantly higher lipid levels (1.5 and 1.9- fold, respectively) than lotic fish. Lentic L. alexandri had significantly higher eicosapentaenoic acid (EPA) levels (4×) than cultured or lotic L. alexandri. Docosahexaenoic acid (DHA) levels were the highest in lentic fish, followed by lotic fish. Lentic fish had greater proportion of fatty acid ω6/ω3 than lotic or cultured fish. The results of this study showed that L. alexandri is a lean fish (1-2% of total lipids) and that the environment has a great influence on the fatty acid profile. These results may be a reference for further studies, primarily as a source of information for conservation L. alexandri through restocking and the development of commercial projects of aquaculture.(AU)

Lophiosilurus alexandri é um peixe de água doce, carnívoro, endêmico da bacia do rio São Francisco e encontra-se vulnerável a extinção. Neste estudo, analisamos a composição química (umidade, cinzas, lipídeos e proteína), o perfil de ácidos graxos e qualidade nutricional (índices de aterogênicidade e trombogenicidade, razão entre ácidos graxos hipocolesterolêmicos e hipercolesterolêmicos e ω6/ω3) de L. alexandri em ambientes lóticos (rio), lênticos (hidrelétricas), sob alimentação natural, e em laboratório, com condições controladas e alimentados com dietas comerciais. Os peixes cultivados e capturados em ambientes lênticos apresentaram níveis lipídicos significativamente mais altos (1,5 e 1,9 vezes, respectivamente) do que os peixes cultivados em ambientes lóticos. Os animais cultivados em ambiente lênticos, apresentaram níveis significativamente mais altos de ácido eicosapentaenoico (EPA) (4×) que os animais cultivados em laboratório e ambiente lóticos. Os níveis de ácido docosaexaenoico (DHA) foram os mais altos em peixes lênticos, seguidos pelos peixes lóticos. Os peixes lênticos apresentaram melhor proporção de ácidos graxos ω6/ω3 que peixes lóticos ou de cativeiro. Os resultados deste estudo mostraram que L. alexandri é um peixe magro (1-2% do total de lipídios) e que o ambiente tem uma grande influência no perfil de ácidos graxos. Esses resultados podem ser uma referência para novos estudos, principalmente como fonte de informações para sua conservação por meio do repovoamento e desenvolvimento de projetos para sua criação comercial.(AU)