Brown seaweeds as a feed additive for Litopenaeus vannamei reared in a biofloc system improved resistance to thermal stress and white spot disease

This study evaluated the combined use of the brown seaweeds Sargassum filipendula (S) and Undaria pinnatifida (U) dry biomass as feed additive for Pacific white shrimp reared in biofloc system, and its effect on shrimp performance, gut microbiota, hematoimmunological parameters, resistance to acute thermal stress and challenge with White Spot Syndrome Virus (WSSV) associated with thermal fluctuation. Prior to stocking, it filled each tank with water from a biofloc matrix tank (160 L)+ seawater (240 L, salinity: 33 g L-1), then stocked with 300 shrimp m(-3) (similar to 3.8 g). During the experiment (five weeks), shrimp were fed three diets: without (control) and with 1%:2% and 1%:4% (S:U) of seaweed addition (all in quadruplicate); and alkalinity was maintained above 150 mg L-1 with calcium hydroxide and solids between 400-600 mg L-1 using clarifiers. No significant differences were found in survival, feed conversion ratio, and growth among treatments. Shrimp from 1S:2U treatment showed the highest gut bacterial diversity. Additionally, animals from seaweed-fed treatments, especially 1S:2U, displayed lower abundance of Vibrionaceae and higher of Flavobacteriaceae compared to control. Only shrimp from 1S:4U treatment showed higher hemato-immunological parameters (except total hemocyte count) than control. Animals from 1S:2U had lower cumulative mortality (27%) than 1S: 4U (48%) and control (50%) after acute thermal stress. Meanwhile, shrimp from 1S:2U (26%) and 1S:2U (34%) showed lower cumulative mortality after WSSV challenge + thermal fluctuation than control (68%). Therefore, the dietary addition of both brown seaweeds caused beneficial physiological effects for L. vannamei without impairing its performance.