The aim of this study was to investigate the effects of different levels of Origanum onites L. essential oil as feed additives on the growth performance, antioxidant activity and disease resistance of rainbow trout. Fish (26.05 AE 0.15 g) were fed the experimental diets supplemented with four different concentrations (0.125, 1.5, 2.5 and 3.0 mL kg À1 ) of O. onites essential oil for 90 days. Fish fed diets containing essential oil of O. onites had significantly higher final weight than the control group. Feed conversion ratio in fish fed diets containing 1.5 and 3.0 mL kg À1 essential oil of O. onites was improved than other treatments (P < 0.05). The lowest feed conversion efficiency ratio was recorded in the 0.125 mL kg À1 group of O. onites. Antioxidant status of fish was assayed for levels of plasma superoxide dismutase (SOD) and plasma catalase (CAT) activity. Lysozyme activity in plasma was significantly higher in fish fed diet containing 3.0 mL kg À1 essential oil of O. onites (P < 0.05). After 8 weeks of feeding, fish were challenged with Lactococcus garvieae and cumulative mortality was recorded over 15 days. Dietary administration of 0.125, 1.5 and 2.5 mL kg À1 O. onites significantly reduced fish mortality (P < 0.05). The 3.0 mL kg À1 diet showed no mortality after challenged with L. garvieae. These results suggested that the essential oil of O. onites could be applied as growth promoter and also improved disease resistance when added to rainbow trout feed.

In the present study, the chemical composition and antifungal activity of the essential oils of the three Lamiaceae species, black tyme (Thymbra spicata L.), oregano (Origanum onites L.) and savory (Satureja tymbra L.) against Saprolegnia parasitica Coker strains (3) were evaluated. The composition of oils was analysed by gas chromatography/mass spectrometry (GC/MS). The major constituent of the oils was carvacrol (82.68% in Thymbra spicata, 82.24% in Origanum onites and 52.38% in Satureja tymbra). The antifungal activity of essential oils was determined by a tube dilution and disc diffusion method. All essential oils inhibited fungal strains at concentration of 100 lL mL À1 . The essential oil of O. onites and T. spicata was the most active (MIC 10 and 50 lL mL À1 , respectively). Thymol did not show inhibiting activity. The essential oils exhibited stronger inhibition than pure carvacrol. Essential oil derived from Tymbra, Origanum and Satureja species has the potential to be used as health control of rainbow trout (Oncorhyncus mykiss) against S. parasitica infection. This study describes the antifungal activity of three essential oils for developing alternative and native control methods against Saprolegniasis.

In the present study, the chemical composition and the antifungal properties against Saprolegnia parasitica (in vitro and in vivo) of the essential oils of thyme (Satureja cuneifolia) from Mediterranean region of Turkey were evaluated for the first time. The composition of oils was analysed using gas chromatography/mass spectrometry (GC/MS). The major constituents of oil of S. cuneifolia were cavracrol (46,84%) and cymene (16.90%). Antifungal effects of S. cuneifolia essential oil against S. parasitica strains (A1 and E1) were detected by disc diffusion and tube dilution assays. The antifungal effect of S. cuneifolia was determined to be stronger against S. parasitica E1 isolate (MIC 50 lL mL À1 , MLC 250 lL mL À1 ) compared with S. parasitica A1 isolate (MIC 50 lL mL À1 , MLC 500 lL mL À1 ). Following in vitro assays, effective doses of S. cuneifolia for disease control in rainbow trout eggs experimentally infected with S. parasitica were investigated. For this aim, infected eggs were treated with the essential oil (0, 5, 10, 20 and 50 ppm) during incubation period (21 days) after fertilization. Formalin (5 mL L À1 ) was used as positive control. Hatching rate of eggs at the end of incubation period were calculated. The highest hatching rates were recorded in S. parasitica E1 strain at 5 and 10 ppm concentrations of S. cuneifolia and in S. parasitica A1 strain at 10 and 20 ppm (P < 0.05).

The present experiment was conducted to describe the effects on histology (experiment 1) and nutrient digestibility (experiment 2) of rainbow trout fed with diet containing O. onites oil. Diets were prepared with supplemented in different concentrate (0, 0.125, 1.5, 2.5, 3.0 ml kg -1 ) of O. onites oil. A total of 1050 trout (body weight 26.05 ± 0.15 g) were randomly stocked into 15 tanks. The experiments were done in triplicate.In the experiment 1, rainbow trout were fed during 90 day for histology analysis. Five fish samples from per tank were taken at the end of the experiment. Liver and kidney histopathology of the control fish showed a normal histological architect without indication of any deformity. Slightly necrosis or degeneration were observed in liver and kidney samples of fish fed with high level of O. onites oil in diets. In the experiment 2, nutrient digestibility study was conducted for 2 week in following of the histology experiment. Nutrient digestibility was determined using 0.5 % Cr 2 O 3 as an indicator to diet. Feces were collected by siphon from bottom of tanks during 2 week. The end of the experiment, dry matter, protein and lipid digestibility did not affect with supplemented in different concentrate of O. onites oil to trout diet.

Bu çalışmanın amacı gökkuşağı alabalığı yemine farklı oranlarda eklenen Origanum vulgare L. uçucu yağının büyüme performansı, lizozim ve antioksidan aktiviteleri ve hastalık direnci üzerine etkilerinin belirlenmesidir. Balıklar (26-27 g), dört farklı konsantrasyonda (0,125, 1,5, 2,5 ve 3,0 ml/kg) O. vulgare uçucu yağı ilave edilmiş yem ile 90 gün boyunca beslenmiştir. O. vulgare uçucu yağı içeren yemle beslenen gruplarda sadece 0,125 ml/kg konsantrasyonu hariç diğer gruplarda büyüme değerlerinde kontrol grubuna göre önemli bir artış belirlenmiştir (P<0,05). Balıklardaki yem dönüşüm ve yem değerlendirme oranları ise 1,5 ve 3,0 ml/kg oranında O. vulgare uçucu yağı içeren yemle beslenen gruplarda diğer gruplara göre artış göstermiştir (P<0,05). Balıkların antioksidan enzim aktiviteleri (plazma süperoksit dismutaz (SOD), plazma katalaz (CAT)) ve lizozim aktivitesi belirlenmiştir. Plazma süperoksit dismutaz (SOD) ve lizozim aktivitesi düzeyleri kontrol grubuna göre O. vulgare uçucu yağı ile beslenen diğer gruplarda yüksek seviyede saptanmıştır. in vivo antibakteriyel aktivitenin tespiti amacıyla, balıklara V. anguillarum patojeni ile deneysel enfeksiyon uygulamaları yapılmış ve O. vulgare uçucu yağı içeren yemle beslenen tüm gruplarda ölüm oranında önemli derecede azalma tespit edilmiştir (P<0,05). Sonuç olarak, O. vulgare uçucu yağının balık yemine ilave edilmesi balıklarda büyümeyi destekleyici, lizozim ve antioksidan aktiviteyi arttırıcı ve aynı zamanda patojenlere karşı direnci artırıcı bir etki göstermiştir.