Improvement of rotifer Brachionus plicatilis population growth dynamics with inclusion of Bacillus spp. probiotics Ian C. Zink 1 , Philippe A. Douillet 2 & Daniel D. Benetti 1 1 Aquaculture Division, Marine Affairs Department, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA 2 Ecomicrobials LLC, Miami, FL, USA Correspondence: I C Zink, Aquaculture Division, Marine Affairs Department, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA. E-mail: izink@rsmas.miami.edu Abstract Due to growing interest in bacterial probiotic incorporation within juvenile marine finfish production, multiple commercial products are cur- rently available. The following trial was conducted to test the effect of incorporation of a commercially available Bacillus spp. probiotic blend (EcoAqua) on population growth dynamics of the rotifer Brachionus plicatilis. Incorporation consisted of 0.1 mL L 1 daily probiotic additions directly to rotifer cultures and 0.1 lL mL 1 additions to feed mixtures during preparation. Probiotic-treated cultures’ daily mean populations were found to be significantly greater (P a(2),4,4 < 0.05) on multiple culture days. This trend was confirmed as significant (P a(2),1,45 < 0.001) using ANCOVA. Logistic population growth curves fit for each treatment were statistically non-coincident (P a(2),5,40 < 0.001). Substantial differences between treatment and control parameter estimates were observed; however, statistical comparisons could not be employed. Population variability was also reduced by probiotic inclusion as evidenced by lack of signifi- cant, positive correlation for probiotic daily popula- tion standard deviations (r = 0.0022, P = 0.99) and detection of a significant, positive correlation for con- trol absolute value regression residuals (r = 0.50, P = 0.013) with Day of Culture. The tested bacterial probiotic improved rotifer culture population dynam- ics, suggesting potential production benefits from its utilization. Keywords: logistic population growth, Bacillus subtilis, B. licheniformis, B. megaterium, B. lateros- porous, rotifer, probiotic Introduction Traditionally, live feed organisms have been uti- lized as larval finfish diets during rearing (Watan- abe, Kitajima & Fujita 1983; Lubzens, Tandler & Minkoff 1989; Lee & Ostrowski 2001). Despite attempts to develop microdiets to replace live feeds, variable success has been achieved, depend- ing upon the species of finfish being cultured; thus, live feeds utilization remains a necessity (Lee 2003). Rotifers (Brachionus spp.) remain one of the most common live feed organisms utilized during larval finfish rearing (Watanabe et al. 1983; Lubzens et al. 1989; Lubzens & Zmora 2003). The necessity to continuously culture roti- fers and the risk of culture collapse complicates larval finfish hatchery production (Hirayama 1987; Lubzens et al. 1989; Lubzens & Zmora 2003). Bacterial community composition has long been recognized to influence rotifer culture stability and population growth (Gatesoupe, Arakawa & Watan- abe 1989; Yu, Hino, Ushiro & Maeda 1989; Skjermo & Vadstein 1993; Hagiwara, Hamada, Hori & Hirayama 1994; Douillet 2000a,b; Rom- baut, Sauntika, Boon, Maertens, Dhert, Top, Sorge- loos & Verstraete 2001; Tinh, Phuoc, Dierckens, Sorgeloos & Bossier 2006). Community composi- tion influences factors such as water quality reme- diation, nutritional and vitamin supplementation and presence of bacterial toxins (Yu, Hino, Ushiro & Maeda 1989; Rombaut, Dhert, Vandenberghe, Verschuere, Sorgeloos & Verstraete 1999; Douillet 2000a; Dhert, Rombaut, Santika & Sorgeloos 2001; Rombaut et al. 2001; Rombaut, Grommen, © 2011 Blackwell Publishing Ltd 200 Aquaculture Research, 2013, 44, 200–211 doi: 10.1111/j.1365-2109.2011.03023.x