Search

Oxidative stress has been recognized as a conjoint pathological mechanism that contributes to initiation and progression of liver injury, such as that caused by bacterial diseases. Natural antioxidants are considered a rational curative strategy to prevent and cure hepatic diseases involved with oxidative stress. Thus, the aim of this study was to evaluate, for the first time, whether treatment with bactericidal Melaleuca alternifolia essential oil (TTO) nanoparticles prevents or reduces the hepatic damage in silver catfish (Rhamdia quelen) experimentally infected with Pseudomonas aeruginosa (PAO1). Liver samples from fish infected with P. aeruginosa showed increased thiobarbituric acid reactive substances (TBARS), protein carbonylation and advanced oxidation protein product (AOPP) levels, while catalase (CAT) activity was reduced compared to uninfected animals. The prophylactic treatment with nanoencapsulated TTO prevented these alterations. Based on this evidence, we concluded that P. aeruginosa infection causes hepatic damage, evidenced by increased TBARS, protein carbonylation and AOPP levels, which inhibits the antioxidant defense system, contributing to disease pathophysiology. Thus, this treatment may be considered an important approach for the prevention of hepatic oxidative damage caused by P. aeruginosa infection in fish.

This study evaluated the anesthetic potential of thymol and carvacrol, and their influence on acetylcholinesterase (AChE) activity in the muscle and brain of silver catfish (Rhamdia quelen). The AChE activity of S-(+)-linalool was also evaluated. We subsequently assessed the effects of thymol and S-(+)-linalool on the GABAergic system. Fish were exposed to thymol and carvacrol (25, 50, 75, and 100 mg/L) to evaluate time for anesthesia and recovery. Both compounds induced sedation at 25 mg/L and anesthesia with 50–100 mg/L. However, fish exposed to carvacrol presented strong muscle contractions and mortality. AChE activity was increased in the brain of fish at 50 mg/L carvacrol and 100 mg/L thymol, and decreased in the muscle at 100 mg/L carvacrol. S-(+)-linalool did not alter AChE activity. Anesthesia with thymol was reversed by exposure to picrotoxin (GABAA antagonist), similar to the positive control propofol, but was not reversed by flumazenil (antagonist of benzodiazepine binding site), as observed for the positive control diazepam. Picrotoxin did not reverse the effect of S-(+)-linalool. Thymol exposure at 50 mg/L is more suitable than carvacrol for anesthesia in silver catfish, because this concentration did not cause any mortality or interference with AChE activity. Thymol interacted with GABAA receptors, but not with the GABAA/benzodiazepine site. In contrast, S-(+)-linalool did not act in GABAA receptors in silver catfish.

The essential oil of Aloysia triphylla (EOAT) is a promising product with potential use in aquaculture systems. This study evaluated hematological/biochemical responses and survival of silver catfish (Rhamdia quelen) fed a diet containing EOAT and infected by Aeromonas hydrophila. After 21 days of feeding trial, fish were infected with A. hydrophila following a 10-day period of observation. Blood collection was performed before and after the bacterial challenge. Dietary EOAT by itself seems to affect some blood parameters, decreasing total leukocyte, lymphocyte, and neutrophil counts and increasing total protein values. However, 2.0 mL EOAT/kg diet showed a possible potential protective effect after A. hydrophila infection, maintaining the evaluated parameters similar to basal values (from healthy fish before the feeding trial) and promoting survival of silver catfish.