Effects of dietary 60 g kg−1dried distiller's grains in least-cost practical diets on production and gut allochthonous bacterial composition of cage-cultured fish: comparison among fish species with different natural food habits

Abstract

Dried distiller's grain (DDG) is considered as an alternative ingredient of dietary feed due to its high contents of protein, fibre and fat. In this study, 60 g kg-1 of DDG was used to feed grass carp (Ctenopharyngodon idella), bluntnose black bream (Megalobrama amblycephala), gibel carp (Carassius gibelio) and black carp (Mylopharyngodon piceus) for 8 weeks, and its effect on fish production and gut allochthonous microbiota was investigated for the development of a suitable fish feed high in nutrients and low in cost for polyculture freshwater fish. DDG supplementation resulted in the less weight gain and higher feed conversion ratio of black carp (P < 0.05), but had no significant effects on other fish or parameters. PCR–denaturing gradient gel electrophoresis (DGGE) analysis indicated that all four fish species had some common and unique bacteria in their digestive tracts, and the gut microbiota of bluntnose black and gibel carp fed the control diet and DDG diets were very similar (Cs > 91%); of them, the total counts of intestinal bacteria studied by qPCR increased in grass carp (P < 0.05) and depressed in black carp (P < 0.05) when fed dietary DDG. Thus, we assumed that dietary DDG modulated production and gut microbiota of fish in a host-specific way.