Brown seaweeds as feed additive for white-leg shrimp: effects on thermal stress resistance, midgut microbiology, and immunology

This study evaluated the midgut microbiology, hemato-immunological parameters and the resistance to thermal shock of the white-leg shrimp Litopenaeus vannamei fed with diets containing 0.5, 2, and 4% of the brown seaweeds Undaria pinnatifida and Sargassum filipendula. Shrimp were reared in clear seawater for 15 days in seven 800-L tanks with 100 shrimp (5.9 ± 0.2 g), under constant aeration and temperature (29 °C), with 80% daily water exchange. Animals were fed four times per day (6% of biomass) during the experimental period. At day 16, bacterial count of midgut and hemato-immunological parameters were assessed before the thermal shock; during thermal shock, shrimp were transferred from seawater at 29 to 12.5 °C for 1 h, and then back to 29 °C, and kept for 48 h to estimate the cumulative mortality. Animals fed with 4% of U. pinnatifida had lower Vibrio spp. quantity in the midgut and showed an overall improvement of evaluated hemato-immunological parameters; however, only phenoloxidase activity was statistically significant. Those fed with 0.5 and 2% of S. filipendula showed lower cumulative mortality after thermal shock, in comparison with control and those fed with 4% of this species. Increasing levels of U. pinnatifida had negative effects on thermal shock resistance. In conclusion, U. pinnatifida enhances shrimp immunity and specifically inhibit Vibrio spp., while S. filipendula increases shrimp resistance to thermal variation.