Organic acids or their salts are promising feed additives for aquatic animals to improve growth performance. We determined the effect of supplementing diets with sodium salts (formate, acetate, lactate, propionate, butyrate, fumarate, succinate and citrate) on trypsin and chymotrypsin activities, in vitro digestibility and zootechnical performance in the whiteleg shrimp (Litopenaeus vannamei). Shrimp trypsin and chymotrypsin activity increased in the presence of acetate and propionate and decreased in the presence of lactate and citrate. The highest in vitro protein digestibility of the experimental diets, using shrimp enzymes, was obtained for diets containing fumarate and succinate, which was significantly greater than the control diet (no supplements). In a growth trial, the highest final weights were in shrimp fed diets supplemented with fumarate, succinate, butyrate and propionate, increasing 53%, 46%, 38% and 29%, respectively, compared to the control. Shrimp that were fed diets with fumarate digested more feed and had a feed conversion ratio 23% higher than the control shrimp. Shrimp survival did not differ among treatments. We concluded that organic salts in the diet modify digestive enzymatic activity and in vitro protein digestibility of whiteleg shrimp. Fumarate, succinate, butyrate and propionate have potential as feed additives for L. vannamei.

The farming of hybrid surubins in Brazil has been affected by bacterial diseases. To avoid this problem, the development of prophylactics such as probiotics has proved to be a promising tool against bacterial outbreaks. This study evaluated the dietary supplementation with lactic acid bacterium Weissella cibaria and its probiotic action in the intestinal tract focusing the hemato‐immunological parameters, histology and electron microscopy. A total of 96 fish were maintained in a recirculation system and divided into 12 tanks, two treatments (supplemented and unsupplemented fish) and six replicates. Fish were fed supplemented commercial diet with W. cibaria for a period of 45 days, and the unsupplemented fish were with commercial feed without probiotic. The numbers of red blood cells, thrombocytes and lymphocytes were higher in supplemented fish after 45 days (P < 0.05). The percentage of phagocytosis, the agglutination titre and the total immunoglobulin concentration were higher in fish fed probiotic. Fish fed supplemented diet presented increased length and width of the intestinal villi, the number of goblet cells and villi's perimeter. The probiotic W. cibaria was capable of colonizing and benefitting the surubins' gastrointestinal tracts, improving intestinal health and the hemato‐immunological parameters of fish.

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