Óleos essenciais de Lippia gracilis e Cymbopogon citratus na dieta de tambaqui (Colossoma macropomum): efeito sobre desempenho, parâmetros hemato-imunológicos e resistência frente Aeromonas jandaei

Abstract

The use of alternative immunostimulants in aquaculture, such as essential oils, is of great relevance, mainly because they have a beneficial effect on the immune responses of fish and because they have antimicrobial potential. Essential oils (EO) from Lippia gracilis and Cymbopogon citratus showed in vitro antimicrobial activity against species of interest in fish farming, such as Aeromonas jandaei and Aeromonas hydrophila. Therefore, the present study aimed to evaluate the effect of including EO from L. gracilis and C. citratus in the diet of tambaqui (Colossoma macropomum) on growth, hemato-immunological responses before and after stimulation with A. jandaei. In chapter 1, a bibliographical review was carried out on the use of EOs as immunostimulant and reported how the oils act by improving the physiological parameters of the fish. In chapter 2, the in vivo study using the inclusion of L. gracilis and C. citratus EOs in the tambaqui diet was described. The study was carried out using a completely randomized design, with 5 treatments (T1= 0.0 g kg-1; T2= 5.0 g kg-1 of L. gracilis EO; T3= 10.0 g kg-1 of EO of L. gracilis; T4= 5.0 g kg-1 of C. citratus EO; T5= 10.0 g kg-1 of C. citratus EO) and 4 repetitions. The EOs were added to the commercial feed (32% CP) and this was given to the fish (n=240), twice a day, for 60 days. After this period, the procedure of biometrics and blood collection of the fish was carried out for hematological, biochemical and immunological analyses. With regard to blood parameters, no statistically significant difference (p<0.05) was found in the values of hematocrit, hemoglobin, erythrocytes, mean corpuscular hemoglobin, mean corpuscular volume and mean corpuscular hemoglobin concentration. Both in the biochemical parameters - total proteins, albumin and globulin - and in the immunological parameters - respiratory activity of leukocytes and concentration of lysozyme - there were no statistical differences between the treatments with EOs. However, a significant reduction in aspartate aminotransferase (AST) values was observed in the treatment containing 5 g kg-1 of L. gracilis EO compared to the other treatments. After 60 days of feeding, the fish had their immune system stimulated with A. jandaei (108 CFU mL-1), but no mortality was observed in the 15-day period, as well as there was no effect on lysozyme and respiratory activity of leukocytes. However, changes in some blood parameters 10 days after the challenge with the bacteria were recorded: control treatment showed a significant reduction in mean corpuscular volume (MCV) values in relation to treatment with 5 g kg-1 of L. gracilis EO, and the total protein values of fish belonging to the control treatments and 10 g kg-1 of L. gracilis EO were significantly lower in relation to the treatment with 5 g kg-1 of L. gracilis EO. In conclusion, the inclusion of EOs from L. gracilis and C. citratus showed non-deleterious effects on fish health, since they did not negatively affect the zootechnical performance of the fish, nor the survival rate after challenge with A. jandaei.