This study investigated the efficacy of essential oils of Lippia alba (EOLA) citral chemotype and Lippia origanoides (EOLO) and their effects on ventilatory frequency (VF) of silver catfish, Rhamdia quelen. Fish were exposed to 50-300 µL L −1 of EOLA and 25-300 µL L −1 of EOLO to determine induction times to sedation, anesthesia, and recovery. Moreover, VF was determined in fish exposed to 5 or 10 µL L −1 of EOLA and of EOLO for 8 h. The increasing concentration of essential oils proportionally decreased sedation and anesthesia induction times. The highest EOLA concentration increased VF of fish from the control group at 1 h of exposure, but VF decreased at both EOLO concentrations after 2 h. The EOLA citral chemotype and EOLO were effective sedatives and anesthetics for silver catfish. However, EOLO was the most suitable sedative for additional studies regarding fish transport as it reduced VF and did not induce VF increase in silver catfish. The EOLA citral chemotype and EOLO are effective sedatives and anesthetics for silver catfish. Moreover, the EOLO is recommended for transport of silver catfish, because it maintains the ventilatory frequency constant, avoiding a possible metabolic stress.

This study examined ammonia, urea, creatinine, protein, nitrite, nitrate, and phosphorus (P) excretion at different water hardness, humic acid, or pH levels in silver catfish (Rhamdia quelen) juveniles. The fish were exposed to different levels of water hardness (4, 24, 50, or 100 mg L(-1) CaCO3), humic acid (0, 2.5, or 5.0 mg L(-1)), or pH (5.0, 6.0, 7.0, 8.0, or 9.0) for 10 days. The overall measured nitrogen excretions were 88.1% (244-423 μmol kg(-1 )h(-1)) for ammonia, 10.9% (30-52 μmol kg(-1 )h(-1)) for creatinine, 0.02% (0.05-0.08 μmol kg(-1 )h(-1)) for protein, 0.001 % (0.002-0.004 μmol kg(-1 )h(-1)) for urea, 0.5% (0.64-3.6 μmol kg(-1 )h(-1)) for nitrite, and 0.5% (0.0-6.9 μmol kg(-1 )h(-1)) for nitrate, and these proportions were not affected by water hardness or humic acid levels. The overall P excretion in R. quelen was 0.14-2.97 μmol kg(-1) h(-1). Ammonia excretion in R. quelen usually was significantly higher in the first 12 h after feeding, and no clear effect of water hardness, humic acid levels, and pH on this daily pattern of ammonia excretion could be observed. Water hardness only affected the ammonia and P excretion of R. quelen juveniles in the initial and fifth days after transfer, respectively. The exposure of this species to humic acid increased ammonia excretion after 10 days of exposure but did not affect P excretion. An increase in pH decreased ammonia and increased creatinine excretion but did not change P excretion in R. quelen. Therefore, when there is any change on humic acid levels or pH in the culture of this species, nitrogenous compounds must be monitored because their excretion rates are variable. On the other hand, P excretion rates determined in the present study are applicable to a wide range of fish culture conditions.

The use of anesthetics in aquaculture ensures better animal welfare and survival during transport and the production cycle. The present study evaluated the anesthetic efficacy of essential oils (EOs) of Lippia alba (EOLA) and Ocimum gratissimum (EOOG) for pink shrimp Farfantepenaeus paulensis, and EOs of Origanum majorana (EOO) and Cymbopogon citratus (EOC) for white shrimp Litopenaeus vannamei. shrimp were exposed to (i) 500, 750 or 1000 µL L-1 of EOLA or (ii) 50, 100, 150 or 250 µL L-1 of EOOG, and L. vannamei were exposed to (iii) 150, 300 or 500 µL L-1 of EOC or (iv) 400 or 800 µL L-1 of EOO. The induction times were concentration dependent, with a decrease in induction time with the increase of the EOs concentration, but for EOLA, this pattern was observed only for anesthesia. Induction times for sedation and anesthesia were significantly shorter for shrimp exposed to EOC and EOO. The highest concentration of EOOG (250 µL L-1) resulted in 30% mortality. The recovery time was significantly longer for shrimp exposed to 800 µL L-1 of EOO compared to the other EOs. Overall, the action of EOs significantly differed between the two shrimp species. In conclusion, the tested EOs effectively anesthetized F. paulensis and L. vannamei.

This study evaluated the effects of continuous exposure to the essential oil of Cymbopogon citratus (EOC) on behavioural and biochemical parameters in shrimp Litopenaeus vannamei. Adult shrimp were randomly placed in aquaria and divided into the following groups: control (pure seawater), ethanol (360 μl L−1 of ethanol) and 5 or 10 μl L−1 EOC for 6 h. Shrimp movements were recorded using a camera for 5 min at the following timepoints: 0, 1, 2, 4 and 6 h of exposure. Light sedation and behavioural changes were observed in shrimp in the 10 μl L−1 EOC group. The total antioxidant capacity against peroxyl radicals (ACAP) in the gills and hepatopancreas of shrimp exposed to 10 µl L−1 EOC was higher than control, whereas, in the muscle, it was lower in those exposed to 5 µl L−1 EOC. In the gills and hepatopancreas, reduced glutathione (GSH) was increased in the control group. Sulphhydryl groups associated with protein (P‐SH) were decreased in the gills of shrimp exposed to 10 μl L−1 EOC. Thiobarbituric acid reactive substance levels, indicative of lipid peroxidation, were higher in the gills and hepatopancreas of shrimp exposed to ethanol, which indicates ROS formation. It is concluded that EOC reduced the swimming behaviour of L. vannamei and improved their tolerance with up to 6 h of exposure.

The aim of this study was to determine the preferred pH in silver catfish Rhamdia quelen juveniles acclimated to different water hardness and the effect of shelters and infection by Ichthyophthirius multifiliis. Fish were acclimated for two weeks at different water hardness levels (4, 24, 50, or 100 mg CaCO 3 L -1) and then transferred to a polyethylene tube with a pH gradient ranging from 3.5 to 11.7 and maintaining the same hardness. The position of the fish in the pH gradient was observed at 1, 2, 4, 6, 8, 10, and 12 h after transfer. Acclimation to different water hardness did not change pH preference of uninfected silver catfish (pH 7.30-7.83), and the presence of a shelter at the preferred pH or outside this preferred pH did not change the chosen pH range, either. Consequently silver catfish favored the acid-base regulation over shelter seeking tendency. Juveniles infected with I. multifiliis acclimated to water hardness of 24 mg CaCO 3 L -1 preferred alkaline pH (9.08-9.79). This choice is not explained by the higher Na + levels at alkaline pH compared to neutral pH because infected and uninfected fish choose the same waterborne Na + levels in a Na + gradient with the same pH.O objetivo deste estudo foi determinar o pH preferencial de juvenis de jundiá Rhamdia quelen aclimatados a diferentes durezas da água e o efeito de abrigos e infecção por Ichthyophthirius multifiliis. Os peixes foram aclimatados durante duas semanas em diferentes níveis de dureza da água (4, 24, 50 ou 100 mg CaCO 3 L -1 ) e então transferidos para um tubo de polietileno com um gradiente de pH de 3,5-11,7, mantendo a mesma dureza. A posição do peixe no gradiente de pH foi observada 1, 2, 4, 6, 8, 10 e 12 h após a transferência. A aclimatação a diferentes durezas da água não afetou o pH preferencial de jundiás não infectados (pH 7,30-7,83), e a presença de um abrigo no pH preferido ou fora deste pH também não alterou a faixa de pH preferida. Portanto, jundiás favorecem a regulação ácido-base em detrimento a uma tendência de procurar abrigo. Em juvenis infectados com I. multifiliis aclimatados à dureza da água de 24 mg L -1 de CaCO 3 o pH preferencial é alcalino (9,08-9,79). Esta escolha não é explicada pelos maiores níveis de Na + em pH alcalino que em pH neutro porque peixes infectados e não infectados escolheram os mesmos níveis de Na + na água em um gradiente de Na + com o mesmo pH.