Aquaculture handling requires fast anaesthesia, assuming an action-time within 3 min and a recovery time of <5 min. This study aimed to determine the lowest effective concentration (LEC) of eucalyptus (Eucalyptus globulus) essential oil (EEO) administered to Rhamdia quelen and its anaesthetic effects. Analysis of EEO chemical profile showed 1,8-cineole as the main component. Two assays were then carried out. In the first, four concentrations were tested (600, 650, 700 and 750 µl L −1 ). EEO was found to be an effective anaesthetic in R. quelen with LEC of 700 µl L −1 . During this assay, no fish mortality occurred. The second assay evaluated stress. Fish were divided into three groups: control (baseline values, without anaesthetic); eugenol (50 mg L −1 ) and EEO (700 µl L −1 ). In this assay, EEO also inhibited the primary stress response. While cortisol did not increase in the EEO regime, plasma glucose and lactate levels did increase in blood. Meanwhile, eugenol kept all stress indicators equal to those of the control group. Therefore, although EEO has suitable anaesthetic characteristics, it should be used with caution, as it does not prevent changes in plasma glucose and lactate for R. quelen.

This study investigated the effect of the dietary protein concentration on lipid concentrations in fillet and liver and concentrations of lipids in plasma and lipoproteins in African catfish. Two experiments were carried out, in which African catfish were fed diets with various protein concentrations. In experiment 1, semisynthetic diets with various concentrations of casein (350, 450 or 550 g protein/kg) were used. In experiment 2, diets were based on a commercial trout diet supplemented with various amounts of casein or carbohydrates, resulting in protein concentrations between 282 and 545 g/kg diet. In both experiments, the dietary protein concentration had a significant effect on growth, feed conversion ratio and carcass composition. Maximum of body weight gains and feed efficiency ratios were reached in both experiments at the highest dietary protein concentrations. Increasing the dietary protein concentration continuously increased masses of fillets and reduced masses of the liver and adipose tissue in the abdominal cavity. Fish fed the diets with the highest protein concentrations had the lowest concentration of total lipids, triglycerides and cholesterol in the fillets, the highest percentage of polyunsaturated fatty acids (PUFA) in total lipids of fillets and the lowest concentrations of saturated fatty acids (SFA). Fish fed the diets with the highest protein concentration also had the lowest concentrations of triglycerides in the liver, the highest percentages of PUFA in liver total lipids and the lowest percentages of SFA. Moreover, fish fed diets with high protein concentrations (501 and 545 g/kg) had significantly lower concentrations of triglycerides, cholesterol and phospholipids in plasma than fish fed diets with lower protein concentrations. In conclusion, this study shows that the dietary protein concentration does not only influence growth, feed efficiency and carcass composition in African catfish, but also influences their lipid metabolism and lipid concentrations of liver and fillet.