Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture Growth performance of the very small rotifer Proales similis is more dependent on proliferating bacterial community than the bigger rotifer Brachionus rotundiformis Duy V.B. Le a,b , Phuoc N. Nguyen b , Kristof Dierckens a , Dung V. Nguyen a , Peter De Schryver a,1 , Atsushi Hagiwara c , Peter Bossier a,⁎ a Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Ghent 9000, Belgium b Faculty of Fisheries, Hue University of Agriculture and Forestry, Hue 53000, Vietnam c Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki 852-8521, Japan ARTICLE INFO Keywords: Rotifers Proales similis Brachionus rotundiformis Probiotics Growth performance Microbial community ABSTRACT Proales similis and Brachionus rotundiformis are commercially cultured species, which predominantly feed on microalgae. However, the importance of the bacterial community on growth performance of P. similis and B. rotundiformis culture is still unknown. In this study, the effect of limiting the bacterial growth and, as a second aim, the effect of the addition of a small amount of live or dead bacteria on the growth performance and microbial community (MC) of P. similis or B. rotundiformis culture was evaluated for a 10 day culture period. A rotifer culture with non-manipulated MC and fed autoclaved algae was used as the first control, and a culture started in autoclaved sea water and fed autoclaved algae was used as the second control. In order to test a feed effect, probiotics and other bacteria present in the culture system were killed (inhibited to grow) through the addition of an antibiotic mixture (AB) and the rotifer culture performance was compared to that of a culture to which live probionts were added. In the presence of the live probiotic mixture, both rotifers species showed a better growth performance than those without the presence of probiotic mixture or those with the AB added. In addition, the growth performance of the rotifer P. similis is more dependent on proliferating bacterial community than the rotifer B. rotundiformis. The supplementation of these probiotic bacteria not only increased the production of the rotifers, but also had a regulating effect on the microbiota. The bacterial density was below detection limit in TCBS, MRS agar and MA in all treatments using AB during the culture period for both rotifer species. 1. Introduction Rotifera are one of the smallest metazoa of which over 2200 species have been described. Although Brachionus plicatilis was first regarded as a pest in a pond, Japanese researchers soon realized that they could be used as a suitable live food organism for the early larval stages of marine fish. The successful use of rotifers in the commercial hatchery operations of the red sea bream (Pagrus major) encouraged investiga- tions in the development of mass culture techniques of rotifers (Hirata et al., 1998; Fukusho and Iwamoto, 1981; Fukusho, 1989; Dhert et al., 1995; Dhert, 1996). The Brachionus plicatilis species complex is a group of euryhaline rotifers in the Brachionidae family. They are raised in the aquaculture industry as a feed for most fish larvae. A simple classification is still used in aquaculture based on three different morphotypes, namely small (S-type, 100–120 μm), super small (SS-type, 90–110 μm) and or large (L-type, 130–340 μm) rotifers (Dhert et al., 1995; Dhert, 1996; Hagiwara et al., 1995, 2001), although DNA-based characterization has been developed (Gomez and Carvalho, 2000; Papakostas et al., 2006) and currently classified into 15 species (Mills et al., 2016). In 2009, Wullur et al. reported that Proales similis, with a body size of 83 ± 11 μm in length and 40 ± 6 μm in width, is a very small rotifer with a potential as first feed for small-sized mouth marine fish larvae. In aquaculture, the minute monogonont rotifer P. similis recently has been proven to be one of the most suitable live food for the first feeding stage of a variety of marine species with a very small mouth at opening, including the seven-band grouper Epinephelus septemfasciatus, the rusty angelfish Centropyge ferrugata, the humphead wrasse Cheilinus http://dx.doi.org/10.1016/j.aquaculture.2017.03.046 Received 17 October 2016; Received in revised form 26 March 2017; Accepted 29 March 2017 ⁎ Corresponding author. 1 Current address: INVE Technologies, Hoogveld 93, 9200 Dendermonde, Belgium. E-mail address: Peter.Bossier@UGent.be (P. Bossier). Aquaculture 476 (2017) 185–193 Available online 06 April 2017 0044-8486/ © 2017 Elsevier B.V. All rights reserved. MARK