2.5. Data collection and analysis At the end of each experiment, starved and axenic controls were sampled and tested
as described above for bacterial contamination. Cultures were then homogenized by Ž
. shaking and five samples 100–1000 ml were withdrawn for estimation of rotifer
densities. Rotifer population GR for each culture tube was calculated as: GR s ln final density y ln initial density
rculture period in days 4 days
Ž .
Ž .
Ž .
Parametric assumptions were evaluated using Hartley’s test for homogeneity of variances, Tukey’s test for non-additivity and Wilk–Shapiro’s test for normality.
Bacterial treatments were tested under two different feeding regimes in Experiments 2 and 4. These data sets were initially analyzed by two-way ANOVA, with feeding regime
and bacterial treatment as variables. GR in all experiments was then analyzed using
Ž .
one-way ANOVA, followed by Tukey’s range test T-method, Sokal and Rohlf, 1981 to determine differences between bacterial treatments at the 0.05 level of probability.
Ž
U
. Ž
Coefficients of variation V between replicates under four treatments axenic, SW,
. B3 and Alteromonas sp. were calculated in each experiment as in Sokal and Rohlf
Ž .
1981 :
U
V s 100 sd rmean
1 q 1r4 n
Ž .
Ž .
where sd is the standard deviation, mean is the average GR and n is the number of Ž
.
U
replicates n s 4 . Independent V were determined for the different treatments under
each one of the diets in Experiments 2 and 4; therefore, six V
U
values were calculated for each treatment in the four experiments. V
U
values under the SW treatment were compared with the V
U
values determined under the axenic, B3 and Alteromonas sp. Ž
. treatments using the t-test for paired comparisons Sokal and Rohlf, 1981 . All tests
Ž .
were performed with the computer program Statistix 2 NH Analytical Software .
3. Results
No evidence of bacterial contamination was found in either starved or axenic control cultures at the end of the culture period. Axenic rotifers populations grew with all diets
tested. GRs in rotifer populations inoculated with SW bacteria did not differ from those Ž
. obtained with axenic controls Figs. 1 and 2 . Significant differences in GRs between
treatments were found in all experiments. Ž
In Experiment 1, additions of eight cultured bacterial additives B5, Alteromonas sp., .
Ž PH, B3, B2, B4, V. alginolyticus and B1 and five commercial products A1200, A2,
. A6, Acc and A5 resulted in larger GRs than those determined in axenic control cultures
Ž .
Tukey’s, p - 0.05 . The second highest GR was obtained in control cultures fed only Ž
. on axenic I. galbana Fig. 1a .
In Experiment 2, significant differences in GR were determined between feeding Ž
. regimes and bacterial treatments two-way ANOVA, p - 0.05 . Therefore, data sets for
each feeding regime were analyzed by one-way ANOVA. Under the AD feeding regime, Ž
. GRs were significantly larger than in axenic controls Tukey’s, p 0.05 in cultures
Fig. 1. GRs of B. plicatilis cultured under synxenic conditions with different bacterial additives and fed axenic Ž .
Ž . Ž .
Ž . ADs in Experiment 1 a , Experiment 2 b , Experiment 3 c and Experiment 4 d . Results of Tukey’s range
tests are displayed above the histogram. Circles that occur together on any one of the horizontal lines indicate mean values that are not different at the 0.05 level of significance. See Table 1 for details of diets.
Ž .
Ž inoculated with one commercial product A5 and five cultured bacterial additives B5,
. Ž .
Alteromonas sp., B3, B4 and PH Fig. 1b . Under the I. galbana feeding regime, GRs
Ž were significantly improved over axenic controls with all bacterial treatments Tukey’s,
. Ž
. p - 0.05 except for A1200 and A5 Fig. 2a .
In Experiment 3, a negative GR was observed in starved cultures due to mortality of Ž
. Ž
initial rotifer populations Fig. 1c . Addition of four strains Alteromonas sp., B3, B5
. Ž
and B4 significantly enhanced GRs of rotifers over axenic control cultures Tukey’s, .
p - 0.05 . As in Experiment 2, significant differences in GRs were determined between feeding
Ž .
regimes and bacterial treatments in Experiment 4 two-way ANOVA, p - 0.05 . There- fore, data sets for each feeding regime were analyzed by one-way ANOVA. Under the
AD feeding regime, addition of all commercial additives and strain B4 resulted in lower GRs than those determined in axenic controls; however, the differences were not
Ž .
Ž .
significant Fig. 1d . Under the mixed feeding regime C. minutissima q AD , addition of the commercial products AB1 and ABA resulted in lower GRs than in axenic
Ž .
controls, but the difference was significative only for AB1 Tukey’s, p - 0.05
Fig. 2. GRs of B. plicatilis cultured under synxenic conditions with different bacterial additives and fed either Ž .
Ž . axenic I. galbana in Experiment 2 a or a combination of axenic AD and C. minutissima in Experiment 4 b .
Results of Tukey’s range tests are displayed above the histogram. Circles that occur together on any one of the horizontal lines indicate mean values that are not different at the 0.05 level of significance. See Table 1 for
details of diets.
Ž .
Fig. 2b . Under both feeding regimes, addition of strains B3 and Alteromonas sp. did Ž
. improve rotifer GR over axenic controls Tukey’s, p - 0.05 , while addition of strain B5
resulted in GRs that did not differ from those of the axenic controls. V
U
values in cultures seeded with SW bacteria were found to be significantly larger Ž
. than either those calculated in axenic cultures t-test, p s 0.018 , cultures inoculated
Ž .
Ž .
with B3 p s 0.018 or cultures inoculated with Alteromonas sp.
p s 0.025 .
4. Discussion
