Comprehensive assessment of benthic diatom (Amphora coffeaeformis) as a feed additive in Nile tilapia (Oreochromis niloticus) diet

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.