1. Introduction
The Caspian roach is a commercially valuable species in the
Caspian Sea and important prey item for sturgeons [1]. However,
over fishing and deterioration of spawning grounds resulted in
depletion of natural population and Caspian roach is now considered
as a threatened species [2]. Restocking and artificial culture up
to marketable size have been developed by Iranian Shilat organization
to reduce pressure on natural Caspian Sea populations [3].
Although the production remained to achieve the amount that
provide the needs, elevation of fish resistance and performance
through dietary supplements is of great importance in commercial
aquaculture of Caspian roach, especially in sensitive periods (i.e.
larvae and fry culture).
World aquaculture has grown tremendously during the last
years becoming the fastest growing food-producing sector in the
world [4]. Beside this growth, demand for environment friendly
aquaculture, and the use of dietary supplements like pro, pre and
symbiotic as an alternatives of antibiotic increased [5]. Prebiotics,
non-digestible food ingredients that beneficially affect the host by
selectively stimulating the growth of and/or activity of healthpromoting
bacteria in the intestinal tract [20], and other microbial
dietary supplements include probiotics and symbiotic have been
demonstrated to show beneficial effects on growth performance,
survival and disease resistance of fish and shellfish species [5,6].
Galactooligosaccharide (GOS) is a prebiotic, produced through the
enzymatic conversion of lactose and mainly consists of galactose
and glucose molecules [7]. Although several studies investigated
the effects of GOS on endothermic animals [8e10], very limited
information is available on prebiotic properties of GOS in aquatic
animals [11e13]. It has been observed that growth parameters
remained unaffected with GOS applications in hybrid striped bass
(Morone chrysops Morone saxatilis) [11] and Atlantic salmon
(Salmo salar) [12]. However, dietary GOS has shown promising