The concentration of b-carotene in Dunaliella sp. cultured with
nitrogen deficiency was 0.42 mg/mL, which is significantly higher
than that reported by Cifuentes et al. (1996) for Dunaliella salina
also produced in a low nitrogen medium (0.0358 mg/L). This
means that the meal incorporated into the experimental diets
was effectively rich in carotenes.
Significant differences were found for shrimp survival between
the treatment and control groups (Fig. 1). The highest mortality
(44%) was recorded at day 6 (144 h post-infection) in the positive
control group (infected juveniles fed the basal diet), while lower
mortalities were found in T1 and T2 (infected shrimp fed diets containing
1% and 2% Dunalliela meal); the negative control group
(non-infected shrimp fed the basal diet) did not register any mortality
during the trial. The large difference on survival observed
among the negative and positive controls confirm that mortality
may be attributable to WSSV infection. It has been observed that
in shrimp infected with WSSV, the mortality may be up to 100%
at 3 to 10 days after infection (Liu et al., 2009). Wu et al. (2005) infected
Peneus monodon with WSSV and recorded mortalities from
80% to 100% after 8 d. The differences in mortality between the positive
control and T1 and T2 treatment groups suggest a beneficial
effect for the microalgae meal included in the diet. In agreement
with our results, some authors have reported the ability of dietary
carotenes to prevent infections, probably due to their prior conver-