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 this study, a total of 98 lactic acid bacteria isolated from rainbow trout intestines were screened for their probiotic properties. The isolates were tested for their ability to inhibit growth of Vagococcus salmoninarum and Lactococcus garvieae. Based on in vitro antagonism, 10 isolates were selected and evaluated pathogenicity in rainbow trout. Isolates were further investigated for hydrophobicity, bile salts and acid tolerance. These isolates were able to survive low pH and high bile concentrations and showed good adherence characteristics. Isolates were characterized phenotypically, and then, 16S rRNA gene sequence analysis was used for confirmation. Selected lactis M17 2-2, respectively. Our results suggest that these strains could provide an alternative for lactococcosis control in aquaculture. K E Y W O R D Saquaculture, lactic acid bacteria, Lactococcus garvieae, probiotic, rainbow trout, Vagococcus salmoninarum

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).

In this study, juvenile rainbow trout fed with commercial pellets containing kefir provided increased nonspecific immune response and improved disease resistance against lactococcosis and yersiniosis. Kefir was used as a feed supplement at 2, 5, and 10% inclusion rates and several nonspecific immune parameters were observed at day(s) 1, 7, 14, 21, 28, and 35 following the treatment. A total of four experimental groups, including control, was established. The various parameters including hematocrits, nitroblue tetrazolium positive neutrophils, total leukocytes, serum lysozyme activity, total serum protein, and immunoglobulin M (IgM) levels were examined. As a result of this study, kefir‐fed fish had an increase in measured nonspecific immune parameters, especially in the group received the 10% kefir treatment. The challenged fish fed with kefir‐supplemented diet showed a better survival rate against Lactococcus garvieae than Yersinia ruckeri. Kefir supplementation reduced fish mortality significantly against L. garvieae.

A study was conducted to determine the effect of feeding with diets containing kefir on growth performance and fatty acid profile of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous (450 g protein kg−1) and isocaloric (4325 kcal kg−1) diets were prepared in trout feed to contain 0 (control), 20, 50 and 100 g kg−1 kefir. Fish, initial weight of 46 g, were randomly distributed into triplicate 520‐L fibreglass tanks in freshwater flow‐through system. Fish were fed at 4% of the body weight thrice a day for 12 weeks. The results indicated that survival rate ranged from 97.14 to 100% without significant difference among treatments (p > .05). Whole‐body moisture and lipid composition were significantly affected by diets containing different levels of kefir (p < .05), but no differences were determined in protein and ash. Furthermore, the fatty acid profile of flesh showed differences among the groups. The percentages of saturated fatty acid in the flesh lipid decreased, while 18:3n‐3 and polyunsaturated fatty acids were increased at higher substitution levels of kefir grain. The present study showed that up to 100 g kg−1 supplementation of kefir in diets could be improve the fatty acid profile, especially PUFA, in fish flesh without adverse effect on the growth, feed utilization and survival rate of rainbow trout.