Abstract
The oxidative stress facing fish during intensive production brings about diseases and mortalities that negatively influence their performance. Along with that, the increased awareness of omega-3 polyunsaturated fatty acids (omega-3-PUFAs) health benefits has been triggered the introduction of alternative additives in aqua feed that cause not only modulation in fish immune response but also fortification of their fillet. In this context, the role of microalgae mix (NSS) containing
Nannochloropsis oculate
and
Schizochytrium
and
Spirulina
species, which were enriched with bioactive molecules, especially EPA and DHA, was assessed on
Nile tilapia
’s performance, fillet antioxidant stability, immune response, and disease resistance. Varying levels of NSS (0.75%, 1.5%, and 3%) were added to
Nile tilapia
’s diet for 12 weeks and then a challenge of fish with virulent
Aeromonas hydrophila
(
A. hydrophila
) was carried out. Results showed that groups fed NSS, especially at higher levels, showed an improved WG and FCR, which corresponded with enhanced digestive enzymes’ activities. Higher T-AOC was detected in muscle tissues of NSS
3.0%
fed fish with remarkable reduction in ROS, H
2
O
2
, and MDA contents, which came in parallel with upregulation of
GSH
-
Px
,
CAT
, and
SOD
genes. Notably, the contents of EPA and DHA in fillet were significantly increased with increasing the NSS levels. The mean log
10
counts of pathogenic
Vibrio
and
Staphylococcus
species were reduced, and conversely, the populations of beneficial
Lactobacillus
and
Bacillus
species were increased more eminent after supplementation of NSS
3.0%
and NSS
1.5%
. Moreover, regulation of the immune response (lysozyme, IgM, ACH50, NO, and MPO), upregulation of
IL
-
10
,
TGF
-
β
, and
IgM
, and downregulation of
IL
-
1β
,
TNF
-
α
,
HSP70
, and
COX
-
2
were observed following dietary higher NSS levels. After challenge, reduction in
A. hydrophila
counts was more prominent, especially in NSS
3.0%
supplemented group. Taken together, the current study encourages the incorporation of such microalgae mix in
Nile tilapia
’s diet for targeting maximum performance, superior fillet quality, and protection against
A. hydrophila.