Diets supplemented with carrageenan increase the resistance of the Pacific white shrimp to WSSV without changing its growth performance parameters

This study evaluated the effect of carrageenan from Kappaphycus alvarezii on the growth and health parameters of the Pacific white shrimp Litopenaeus vannamei . Shrimp (initial weight 4.5 ± 0.5 g) were farmed in 800 L tanks for five weeks, at a density of 30 shrimp tank ‐1 , under controlled temperature (28.5 °C), constant aeration, 100% water exchange four times week ‐1 , and fed four times day ‐1 . Five experimental diets containing 0%, 0.5%, 1.0%, 1.5%, and 2.0% of carrageenan were used and followed a complete randomized design (all in triplicate). After the 5-week feeding trial period, we assessed shrimp growth parameters (survival, feed conversion, total, weekly, and final weight gain) as well as immunological and gut microbiota profiles. A total of 30 shrimp from each feeding treatment were infected with a inoculum of the white spot syndrome virus (WSSV), and the resulting cumulative mortality was monitored for 96 h. WSSV infection results showed that shrimp that received carrageenan supplementation had higher survival rates (80%, 75%, 85%, and 70%, respectively, increasing carrageenan, 0.5 to 2%) compared to the control group (45%). No significant differences in weight gain and food conversion were observed among the feeding treatments relative to the control diet. Final weight varied from 8.50 g to 10.30 g, and the food conversion rate from 1.42 to 1.67. Also, no significant differences were found in intestinal microbiota and immunological parameters. Metagenomic analysis showed that adding 0.5% of carrageenan in the diet caused an increase in the relative abundance of an unassigned bacterium (from Rhodobacteraceae family) and bacteria from two other families, Rubritaleaceae and Caldilineaceae, with 1.0% and 1.5% addition levels, respectively. Adding low levels of carrageenan (up to 1.5%) to the feed of the Pacific white shrimp might benefit their microbiota composition as well as their capacity to respond to WSSV infection, without causing any loss in growth performance and health status. • All carrageenan dietary levels reduced shrimp mortality after WSSV challenge. • Carrageenan dietary addition affected the abundance of specific bacteria in the gut. • All carrageenan dietary levels did not affect shrimp growth. • Carrageenan addition in the diet had minor effect on shrimp immune parameters.