In this study, the relatively high mortality during
the trial might be associated with the short acclimation
period (3 days after transportation) and/or
the cultivation conditions. However, as all the
experimental parameters were detected on the
remaining surviving prawns at the end of trial,
the different response of prawns between control
and treatment groups remains valid reflecting the
microalgal nutrient efficacy in this study. Prawns’
survival rate was elevated significantly in the
Melosira feed group. The mean value of survival
rates in other microalgae diet groups was numerically
higher than the control level at different
degrees, albeit of statistic insignificance. This outcome
was coincident with increased astaxanthin
content of these prawns’ flesh, as well as a robust
immune response. In this study, we selected
phagocytosis and SOD activities in the haemolymph
to detect immune response, as they are
widely used as health condition indices in aquatic
animals
Although there was no statistical difference of
phagocytosis rate and/or SOD activity in both CPC
and Chlorella groups compared with the control
group, higher mean values were detected in the
prawns fed microalgal additives. In comparison,
marine microalgae species showed better efficacy
than freshwater ones, which confirms that marine
phytoplankton have a major role in improving
prawn immune response