The aim of this study was to detect effects of bitter orange (Citrus aurantium) essential oil, commonly called neroli oil (NO) (0, 0.25, 0.50, 1, and 1.5% referred to as NO₀ NO_0.25, NO_{0. 05}, NO₁ and NO_1.5, respectively) on growth performance output and expression levels of some growth-related genes in the muscle tissue and some immune-related genes in the head kidney and pathological differences in digestive system organs of common carp Cyprinus carpio. The NO_0.25 group had a large improvement in growth efficiency at the end of the 60-day feeding cycle. Real-time PCR (Bio RAD, USA) system was used to detect variations in gene expression levels. Furthermore, NO supplementation of up to 0.25% in muscle tissue controlled the release of growth hormone (GH) and insulin-like growth factor I (IGF-I). Furthermore, in the NO_0.25 treatment category, immune response gene levels TNF-α, IL-8 and IL-1ß increased in head kidney tissue. In the histological examination of the liver and intestine, there were significant differences between fish fed with N₁ and N_1.5 diets. This study confirms that dietary supplementation of NO up to 0.25% can improve common carp growth efficiency and increase the expression of genes (GH and IGF-I) related to muscle growth, TNF-α, IL-8 and IL-1ß genes related to immune status, and liver and intestine histological status of common carp.

In this research the effects of oat Avena sativa extract on the non-specific immune system of common carp (Cyprinus carpio) was examined. For this purpose, the fishes (average weight 9.91 ± 1.52 g) were fed with 5 g kg ⁻¹, 10 g kg ⁻¹ and 20 g kg ⁻¹ oat extract supplemented diets for 60 days. Following 60 days of feeding, the fishes were injected with Aeromonas hydrophila and mortalities were recorded. Lysozyme and myeloperoxidase activity, improved in all groups that received feed supplemented with oat extract. Serum glucose and cholesterol decreased while total protein and albumin in fish increased with the use of the diet supplement with oat extract. Haemoglobin (Hb), mean cell hemoglobin (MCH) and mean cell haemoglobin concentration (MCHC) increased with diet supplemented with oat extract. Oat extract at the concentration of 10 g kg⁻¹ showed significantly higher relative percentage survival (67%) when compared with the control against A. hydrophila injection. Also the dietary supplementation with oat extract caused a significant increase in growth parameters (final weight (FW), weight gain (WG), specific growth rate (SGR) and feed conversion ratio (FCR), when compared to non-supplemented control basal diet. The results suggest that A. sativa extract can be used as a feed supplement to enhance fish immune response and disease resistance against A. hydrophila.