Enhancement of non-specific immune responses in common carp, Cyprinus carpio, by dietary carotenoids obtained from shrimp exoskeleton.

The immunostimulatory role of carotenoid extract
from shrimp processing discards was evaluated by
feeding common carp fingerlings with a diet
containing carotenoid extract for 21 weeks at 100
and 200 mg kg�1 astaxanthin levels. Haemoglobin
content was significantly (P < 0.05) higher in
the blood of fish fed with carotenoid diet
(>8.1 g dL�1) compared with that from fish fed
with carotenoid deficient diet (6.86 g dL�1) and
also leukocyte counts were higher (P < 0.05). No
differences (P > 0.05) were observed in total
serum protein, globulin level and albumin-globulin
ratio, but albumin content was higher (P < 0.05).
Respiratory burst activity was significantly
(P < 0.05) higher, the serum lysozyme activity
almost doubled and the serum bactericidal activity
was significantly increased when the fish were fed
with diet containing 200 mg kg�1 of astaxanthin
but no significant differences were observed in
serum trypsin inhibitory activity. There was a
significant (P < 0.05) increase in leukocyte myeloperoxidase
activity due to dietary carotenoids.
Challenging fish with Aeromonas hydrophila after
the feeding period resulted in 50% mortality in
the control group while in the group fed with diet
containing 100 mg kg�1 astaxanthin, the mortality
rate was 15%. No mortality and even symptoms
of infection was not observed in the group
fed with diet containing 200 mg kg�1 of astaxanthin.
The study indicated that carotenoid extract
from shrimp processing discards can effectively be
used as immunostimulants in aquaculture of carps
and dietary carotenoids were found to enhance
various immune defence mechanisms and also
provide protection against the infection of pathogen
A. hydrophila.