Combined or Individual Effects of Dietary Probiotic Pedicoccus acidilactici and Nucleotide on Growth Performance, Intestinal Microbiota, Hemato-biochemical Parameters, and Innate Immune Response in Goldfish (Carassius auratus) Nooshin Mehdinejad 1 & Mohammad Reza Imanpour 1 & Valiollah Jafari 1 # Springer Science+Business Media, LLC 2017 Abstract This study investigated the effect of dietary supple- mentation of probiotic Pedicoccus acidilactici and nucleotide (separately or combined) on growth performance, intestinal microbiota, hemato-immunological parameters, and immuni- ty response in goldfish (Carassius auratus). Fish (average weight 5–6 g) were acclimatized and divided into eight exper- imental diets supplemented with P . acidilactici of different concentrations (0.1, 0.2, and 0.3% diet) and nucleotides (0 and 0.5% diet) for 6 months. Fish fed with experimental diets showed significant differences in terms of final weight, weight gain, feed conversion ratio, daily growth rate, and condition factor when compared to control diet (P < 0.05). Fish fed with probiotic (0.3%) separately and combined with nucleotide (0.5%) had highest RBC and WBC when compared to other diets (P < 0.05), while the highest values for Hb and Hct as well as total protein, glucose, albumin, and globulin were observed in probiotic (0.2%) and nucleotide (0.5%) combined diet. Serum lysozyme and anti-protease activities were signif- icantly higher in probiotic (0.1 and 0.2%) and nucleotide (0.5%) combined diets. Similarly, these two diets combined showed the highest colonization of P . acidilactici when com- pared to other diets. In conclusion, combined dietary probiotic and nucleotide improve the growth performance, hemato- biochemical parameters, and intestine growth in C. auratus. Keywords Blood parameters . Goldfish . Growth performance . Intestinal microbiota . Nucleotide . Pedicoccus acidilactici Introduction The commercial production of ornamental fish is gaining mo- mentum as a global component of international trade, fisher- ies, and aquaculture development. The last four decades have witnessed considerable growth and diversification in the inter- national trade of ornamental fish [1]. Goldfish, Carassius auratus (Linnaeus, 1758), a member of the Cyprinidae family, is one of the most popular aquarium fish and is extremely valuable commercially. Goldfish do not only have attractive color but also are hardy and easy to culture, so they make excellent aquarium species and laboratory species. Moreover, their hardiness and ready availability give them scientific value for genetic and physiological research also [2]. Nucleotides are low-molecular-weight biological com- pounds that play major roles in most biological processes [3]. Although early studies on dietary nucleotide supplemen- tation in fish nutrition could be traced to the 1970s, research at that time was mainly focused on the potential chemo- attractive effects of these compounds [4–6]. However, recent research on dietary nucleotides in fish has elucidated that they may improve growth performance and liver function, modify intestinal structure, increase stress tolerance, and modulate innate and adaptive immune responses [7]. The term probiotic is a relatively new word meaning Bfor life,^ and it is currently used to name bacteria associated with beneficial effects for humans and animals [8]. In fact, they offer benefits to the host primarily via the direct or indirect modulation of the intestinal microbiota, which will in turn promote the host’ s immune system and growth, stimulate its enzyme activity, and improve its disease resistance [9]. In the past 20 years, there has been great interest in the application of lactic acid bacteria (LAB) and their metabolic products as potential probiotics for aquaculture to improve growth and survival of fish [10, 11]. LAB are well known by their ability * Nooshin Mehdinejad mehdinejad.nooshin64@gmail.com 1 Department of Fisheries, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Probiotics & Antimicro. Prot. DOI 10.1007/s12602-017-9297-3