Abstract :
Abstract This study investigated effects of dietary olive leaf extract (OLE) on growth performance, hematological parameters and resistance against Yersinia ruckeri in rainbow trout. Four groups were designed including a control diet and OLE added in fish feed at 0.5, 1.0, and 1.5 ml/100 g feed, which were administered for 30 days. The weight gain (WG), specific and absolute growth rate (SGR and AGR), feed conversion ratio (FCR) and feed efficiency ratio (FER) of rainbow trout fed with OLE were found to be significantly (p < 0.05) differed compared with control. Fish fed 1.0 ml/100g feed OLE supplemented diet significantly improved (p < 0.05) WG, AGR and SGR. The lowest FCR was observed with 1.0 ml OLE/100 g diet. An enhancing effect of OLE on hematological parameters occurred, as shown by the significant increase in red blood cell (RBC), white blood cell (WBC) and haematocrit (Ht) parameters in fish fed with 1.0% OLE. Haemoglobin (Hb) level of fish fed the 1.5% added OLE diet was significantly lower than those fed the 0.5 or 1.0% added OLE diet and control groups. Mortality at 14-day post-challenge with Y. ruckeri significantly decreased at all the dietary OLE groups. Dietary OLE at the level of 1.0 and 1.5 ml/100 g feed showed significantly (P < 0.05) higher relative percentage survival (RPS) (73.91 and 78.26%, respectively) against Y. ruckeri infection. The present results suggest that diets supplemented with OLE feed level positively enhance the growth parameters and affords protection from Y. ruckeri.
Keyword :
Keywords: Feed additive, Growth, Olive leaf extract, Rainbow trout, Yersinia ruckeri