Growth performance, intestinal histology, and biochemical parameters of rainbow trout (Oncorhynchus mykiss) in response to dietary inclusion of heat-killed Gordonia bronchialis.

Gordonia bronchialis is a Gram-positive, weakly acid-fast species of the genus Gordonia within the sub-order Corynebacteriaceae of the order Actinomycetales. It is an environmental organism that rarely gives raise to human infections (Arenskotter et al. 2004). Killed preparations of G. bronchialis and some other genera within the order Actinomycetales are potent immune modulators useful in the prevention and treatment of many immune-related diseases in laboratory animal and veterinary medicine (Fontanella et al. 2007; Davila et al. 2011; Marro et al. 2011; Stanford and Stanford 2012; Smaldini et al. 2013). In aquaculture, G. bronchialis improved survival and weight gain in shrimp and young fish, enhanced growth rate and color in Koi carp and reduced its skeletal abnormalities (Stanford and Stanford 2012). There are some studies regarding the effects of immunostimulatory substances on the metabolism of aquatic animals (Castexa et al. 2009; Harikrishnan et al. 2010; Lazado et al. 2010; Weifen et al. 2012). Since there is no information about the effect of G. bronchialis on fish biochemical indices, in the present study the effect of dietary inclusion of heatkilledG. bronchialis on the serum antioxidant activity, serum-specific marker enzymes such as alkaline phosphatase and aspartate aminotransferase, and serum metabolites (triglycerides, cholesterol, uric acid, and glucose) of juvenile rainbow trout was investigated. Furthermore the growth performance and gastrointestinal structure of juvenile rainbow trout fed with heat-killed G. bronchialis was also determined.