This study investigated the effect of the co-feeding of bacteria and microalgae on nitrogen (N) assimilation in an
Artemia franciscana gnotobiotic laboratory culture test. Two strains of bacteria were used, HT3 and HT6, isolated
from previous Artemia laboratory cultures. These were fed in combination with microalga Dunaliella tertiolecta
strains, either the high quality DT 19/6B or the low quality DT 19/27 strain. Each combination of algae and bacteria
was offered in different proportions, i.e. 10/90, 50/50 and 90/10% on a dry weight basis, while the total
amount of food supplied, which was based on a reference algae mono-diet, was kept constant. Mono-diets
consisting of 100% algae and 100% bacteria were added as controls. N assimilation from either food source was
determined by feeding in separate tests 15N labeled microalgae with non-labeled bacteria and vice versa. Axenically
hatched Artemia nauplii were fed these diets for 24 h, after which they were analyzed for 15N content. The
results of 15N analysis showed that the N assimilation from bacteria in Artemia was improved when the bacteria
were 10% replaced by microalgae, and for the combination of DT 19/6B and HT6 this increase was significant
(P b 0.05). Also 50% replacement of HT6 by DT 19/6B resulted in higher, but non-significant, N assimilation
from the bacteria as compared to the 100% bacteria mono-diet. A similar non-significant increase of N assimilation
from DT 19/6B was observed as compared to the 100% algae diet when these algae were up to 50% replaced
by HT6 bacteria. Other combinations of bacterial and microalgal strains generally produced similar or lower N assimilation
as compared to the labeledmono-diet,when the labeled food component (bacteria or algae)was gradually
replaced by the other (algae or bacteria). This study shows that, provided suitable strains are used, offering
microalgae and bacteria together as food for Artemia may result in a synergistic effect in how this filter-feeding
organism takes advantage of the respective food sources. This Artemia study can also be considered as a model
for future research on the feeding biology of other filter-feeding aquaculture organisms.