Four hundred and fifty Nile tilapia (Oreochromis niloticus), each weighing ca. 4 g, were
randomly allocated into five equal groups in triplicate. The first group acts as control
(A0). A1, A2, A3 and A4 groups were fed on rations supplemented with diatom,
Amphora coffeaeformis, at 2.5, 5.0, 7.5 and 10%, respectively, for 63 days. Assessment
of fish growth, biochemical composition, erythrocyte alterations, gonadal maturation,
serum biomarkers, and liver and intestinal pathogens was carried out to identify
fish welfare. Fish were challenged by Aeromonas hydrophila injection for an additional
14 days; then, mortality rate and some blood parameters were monitored. Results
demonstrated that Amphora sp. insignificantly impacted fish growth, but it induced
significant depletion in lipid content. Blood smear investigation indicated erythrocyte
alterations in A4 group compared with A0 group. Male gonadosomatic index and
relative fecundity demonstrated an increment in A3 and A4 groups respectively. A
boost in fish immunity of A3 group was demonstrated through serum biomarkers and
pathogenic bacterial identification in liver and intestine compared with other groups.
Cumulative mortality of stressed fish was 90% in the A0 group and decreased to 30%
in the A3 group. Blood analysis of stressed fish indicated higher tolerance in the A3
group. In conclusion, Amphora sp. can be used as an immunostimulant for increasing
disease resistance under stress conditions.