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Although daily variations in drug pharmacokinetics have been reported for a variety of teleost species, the influence of this daily variation on the cortisol response following anaesthesia remains poorly understood. To address this, two experiments were performed. The first experiment described the daily patterns of cortisol and glucose secretion in tilapia (Oreochromis niloticus). The second experiment investigated how the timing of anaesthetic administration (specifically at mid‐light [ML] or at mid‐dark [MD]) affects the induction and recovery times and plasma cortisol and glucose levels of juvenile Nile tilapia exposed to benzocaine, clove oil or tricaine methanesulphonate (MS‐222). The results revealed that the effect on the stress response associated with the moment when anaesthesia took place (ML or MD) varied according to the treatment (p 0.05) or in the benzocaine‐treated group (ML = 38.7 ± 4.90; MD = 38.60 ± 3.69 ng/dl) (p > 0.05). The highest plasma cortisol level in ML was found in the MS‐222‐treated group. All the tested anaesthetics had similar cortisol levels at MD (p > 0.05).

This study aimed to evaluate the influence of increasing concentrations of dietary dry oregano leaves (DOL), ranging from 0 to 0.15%, on different performance parameters of Nile tilapia. Hence, two separate experimental trials testing growth factors (Trial 1) and innate immunity and disease resistance against Streptococcus agalactiae infection (Trial 2) were conducted with a total of 464 tilapia juveniles and two to four replicates. As a result, dietary inclusion of DOL did not induce significant effects on growth performance, hematological parameters, and fillet composition. However, there were significant differences in lysozyme activity between groups of DOL at 0.075% and the control (0%). Moreover, the bactericidal index of the positive control and groups supplemented with DOL were significantly higher than baseline treatment groups. For disease resistance, there was a reduction of 15% in the relative risk of streptococcosis in fish juveniles after dietary inclusion of oregano at 0.15%. In conclusion, the inclusion of DOL in tilapia diets resulted in no significant gains in terms of growth; nevertheless, the immune system and resistance of tilapia against S. agalactiae infection were significantly improved.

This work evaluated the blood parameters of Lophiosilurus alexandri juveniles submitted to doses of 80, 160, 320, and 640 mg L−1 eugenol (n = 60, 171.59 ± 37.87 g) and 60, 120, 240, and 480 mg L−1 benzocaine (n = 60, 214.87 ± 75.83 g) were tested. For each anesthetic, there was a control group. Thus, anesthesia time and recovery of the analgesia condition were evaluated. Of the 12 animals from each treatment, six went through blood collection after sedation and the other six, 24 h after anesthesia. The survival index for the use of both anesthetics, after 24 h after anesthesia, was 100%. The induction times for eugenol and benzocaine presented an inversely proportional ratio, while the recovery time, a ratio directly proportional to the increase in anesthetic concentrations. Glucose was higher after sedating the animals, regardless of the concentrations tested. The hematocrit had lower values after 24 h after anesthesia at the doses of 320 and 640 mg L−1, while the total protein was not affected during the observations. With the use of benzocaine, glucose was higher at concentrations of 240 and 480 mg L−1. In relation to time, glucose was higher after anesthesia. Total protein had higher values in the doses of 240 and 480 mg L−1. The hematocrit was not affected in the experiment. Concentrations between 80 and 160 mg L−1 eugenol and between 60 and 120 mg L−1 benzocaine may be used in anesthetic procedures of L. alexandri juveniles.

The aim of this study was to evaluate the possible effects of diets supplemented with probiotics and different cinnamon levels (powder and essential oil) on immunological parameters of Nile tilapia after being subjected to acute stress by hypoxia. Three hundred and thirty juvenile male tilapia fish (66.08 ± 2.79 g) were distributed in 30 tanks of 100 L capacity (11/cage) with a water recirculation system. The animals were fed for 71 days with diets containing extruded cinnamon powder at different levels (0.5, 1, 1.5, 2%), cinnamon essential oil (0.05, 0.1, 0.15; 0.2%) and probiotics (0.4%), all in triplicate. At the end of the experiment, the fish (200.36 ± 19.88 g) of the different groups were subjected to stress by hypoxia. Hypoxia was achieved by capturing the animals with a net, keeping them out of the water for three minutes, and then sampling the blood 30 min after the procedure to determine the levels of cortisol, glucose, haematocrit, lysozyme, bactericidal index, total protein, and its fractions. The animals kept blood homeostasis after hypoxic stress. Diet supplementation with 0.5% cinnamon powder improved the fish immune response, since it resulted in an increase of 0.5% in γ-globulin level. Administration of 0.15% cinnamon essential oil resulted in an increase of α1 and α2-globulins, which may be reflected in increased lipid content of the carcass and the hepatosomatic index. More studies are necessary to better understand the effects of these additives for fish immunity.

Environmental factors such as light and temperature present cyclic variations during the day. High temperatures occur during the light phase, whereas low temperatures take place at night (i.e. a daily thermocycle). Although applying thermocycles to fish larvae improves growth in some species, nothing is known about the impact during the early development of the digestive system. The aim of the present research was to investigate the effect of different temperature regimes, cycling versus constant, on the daily rhythms of digestive factors and growth of Nile tilapia (Oreochromis niloticus) larvae. For this purpose, fertilized eggs (stage 1) were divided into two groups: one under a thermocycle (TC) of 31 °C:25 °C day:night and another group at constant temperature of 28 °C (CTE). Photoperiod was set at 12:12 h light/dark cycle. Larvae length was measured on 4, 8 and 13 days post-fertilization (dpf) and samples were collected every 4 h during a 24-h cycle on these days. The expression levels of pepsinogen, chymotrypsinogen, trypsinogen, lipase, maltase, isomaltase, npy and cck were analyzed by qPCR. The results showed that growth was greater when larvae were reared at TC than at CTE. Moreover, on 13 dpf, most analyzed genes (chymotrypsinogen, lipase, maltase, isomaltase, npy and cck) displayed daily rhythms in the TC group but not in CTE, with most acrophases located around mealtime. These rhythms might explain the higher growth rate observed in the TC larvae due to improved synchronization of feed digestion and utilization. These findings could be useful for improving rearing protocols used in tilapia larviculture and enhancing production performance.

An experiment was conducted during 60 days with forty pacu males fed diets supplemented with increasing concentrations of ractopamine (0.00, 11.25, 22.50, 33.75, and 45.00 mg kg−1). Eight fish were evaluated for each experimental diet. Performance and survival rate of the fish were measured. At the end of the experiment, blood was collected to determine the levels of cortisol, triacylglycerol, and protein. Moreover, the liver was collected to determine the activities of glucose-6-phosphate dehydrogenase and malic enzymes. The fillets were collected to determine chemical composition, and histologic cuts were analyzed to verify muscle growth and deposition of adipose tissue between muscle fibers. Increasing concentrations of dietary ractopamine did not change feed intake, fillet yield, fillet content of protein and ash, and frequency of relative distribution of muscle fibers. By increasing the dietary ractopamine concentration, the serum cortisol level was elevated. Ractopamine supplementation (45.00 mg kg−1) increased serum levels of triacylglycerol and protein and reduced the activity of hepatic lipogenic enzymes and the survival rate of the fish, probably in response to the high concentration of circulating cortisol. In addition, the higher level of ractopamine supplementation evaluated in this research impaired the weight gain and feed conversion. However, 11.25 mg kg−1 ractopamine reduced the ether extract level determined in the fillet and the fat deposition between muscle fibers, improving the nutritional quality of meat.

In aquaculture, activities with anesthetic compounds are usually used in order to ensure the welfare of farmed fish, allowing handling out of water with decreased trauma by stress. Presently, there is no information about anesthetic action of eugenol in early life stages of Nile tilapia (Oreochromis niloticus). The objective of this study was to evaluate different concentrations of eugenol for larvae and juveniles of Nile tilapia. Sixty animals were used for each group of weight, group I = 0.02 g; group II = 0.08 g; group III = 0.22 g; group IV = 2.62 g; and group V = 11.64 g. The eugenol concentrations tested were 50, 75, 100, 125, 150 and 175 mg L-1. No mortality was reported during the tests with eugenol. Tilapia larvae with 0.02 g and juveniles around 11.64 g can be anesthetized with eugenol concentrations between 150 and 175 mg L-1, since they determine the shortest sedation time (23 and 72 seconds, for the group of lowest and highest weights, respectively). Na aquicultura, as atividades com anestésicos são normalmente empregadas a fim de assegurar o bem-estar dos peixes cultivados, permitindo a manipulação fora da água diminuindo desta forma o trauma por estresse. Atualmente, não há nenhuma informação sobre a ação anestésica do eugenol em fases iniciais de vida de tilápia do Nilo (Oreochromis niloticus). O objetivo deste estudo foi avaliar diferentes concentrações de eugenol para larvas e juvenis de tilápia do Nilo. Sessenta animais foram usados em cada grupo de peso, o grupo I = 0,02 g; grupo II = 0,08 g; grupo III = 0,22 g; grupo IV = 2,62 g; e grupo V = 11,64 g. As concentrações de eugenol testadas foram 50, 75, 100, 125, 150 e 175 mg L-1. Não houve mortes durante os testes com eugenol. Larvas de tilápia com 0,02 g e juvenis em torno de 11,64 g podem ser anestesiados com concentrações de eugenol entre 150 e 175 mg L-1, uma vez que determinam o menor tempo de sedação (23 e 72 segundos, para o grupo de peso menor e maior, respectivamente).