The wide use of antimicrobial agents in modern food animal production has led to the emergence of antimicrobial resistance worldwide. In aquaculture this has resulted in the emergence of antibiotic-resistant bacteria in aquatic environments, increase of antibiotic resistance in fish pathogens, transfer of resistance determinants to bacteria of land animals and to human pathogens, and alterations of the bacterial flora both in sediments and in the water column. Phytotherapy is based on the use of plants for prevent or treat human or animal diseases. At the beginning of the 20th century, phytotherapy was in competition with modern medicine and in particular with antibiotic molecules.
Recently, the use of essential oils is also rapidly increasing in the aquaculture sector as a means of greater industrial and environmental sustainability. Previous studies showed beneficial effects of essential oils on growth, immunity antibacterial and antiparasitic activities in fish crops. In this study, the modulation of antioxidant defense against oxidative stress exerted by fish d iets supplemented with a basil supercritical extract (BEO) was assessed in rainbow trout Oncorhynchus mykiss. The basil supercritical fluid extracts were obtained from dried clean basil leaves using a supercritical fluid extractor.
The BEO extracted was added to the commercial feed flour in the proportions of 0.5%, 1%, 2% and 3% (w/w) and subsequently mixed with fish oil to obtain a suitable compound for pellet preparation.
A 30-day trial was carried out using 20 square fiberglass tanks supplied by artesian well water (constant temperature of 13?±?1?°C) in an open system (flow-through). The experimental diets (A: control; B: 0,5%; C: 1%; D: 2%; E: 3%) were randomly assigned to the tanks (four replicate tanks per diet).
The daily feed quantity was set at 1% of tank biomass. Eight fish from each experimental group (2 fish per tank; four replicates) were sampled at the middle (15 days; T1) and at the end (30 days; T2) of the experiment. Liver and kidney were sampled from each specimen and stored at -80 °C for biochemical analysis. The levels of stress biomarkers such as superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione reductase, glyoxalase I, glyoxalase II, lactate dehydrogenase, glutathione and malondialdehyde showed a boost of antioxidant pathway in fish fed with 0.5% BEO supplemented diet. Higher BEO supplementation led to failure of activity of several enzymes and depletion of glutathione levels. Malondialdehyde concentration suggests a sufficient oxidative stress defense against lipid peroxidation in all experimental groups, except for 3% BEO supplemented diet. Our results suggest for a supplement of BEO in fish-diet up to 0.5% to avoid potential oxidative pressure in farmed trout.