Integrative transcriptomic and physiological assessment of nanoencapsulated carvacrol and thymol oil as an antioxidant in thermal-stressed white shrimp (Litopenaeus vannamei)

The present study aimed to assess the effects of chitosan nanocapsules loaded with synthetic carvacrol and thymol (structurally analogous to those in oregano oil) on the antioxidant and molecular response of Litopenaeus vannamei subjected to acute thermal stress. Chitosan nanocapsules (of 246 nm) were prepared and incorporated into shrimp feed at eight concentrations in triplicate: 0.0 (0ChNP), 0.033mg g^{- 1} (0.03ChNP), 0.1mg g^{- 1} (0.1ChNP), 0.2mg g^{- 1} (0.2ChNP), 0.3mg g^{- 1} (0.3ChNP), 0.467mg g^{- 1} (0.5ChNP), 0.633mg g^{- 1} (0.6ChNP), and 0.8mg g^{- 1} (0.8ChNP). Twenty-four aquariums, each containing three shrimp (10.25 ± 1.14 g), were fed for two weeks. The first 8 days at 27 ± 0.5 °C, followed by a gradual temperature increase to 39 °C. Thereafter, shrimps were sampled, and the hepatopancreas dissected and divided into two, and individually stored in RNAlater for transcriptomic and qPCR analysis. The groups 0ChNP, 0.03ChNP, and 0.3ChNP were selected for transcriptomic analysis based on their physical appearance, and mortality rate. At 0.03ChNP, significant upregulation of genes associated with innate immunity, vesicular trafficking, and autophagy was detected, suggesting an activated protective response. On the other hand, the qPCR on anti-oxidative enzymes, catalase and glutathione peroxidase, showed lower levels than in the control experiments suggesting reduced oxidative stress when chitosan nanocapsules were supplied, especially with 0.3ChNP. In conclusion, chitosan nanocapsules delivering carvacrol and thymol at 0.3 mg g^{- 1} of feed modulate distinct molecular pathways that contribute to thermal stress resilience in shrimp. Doses below or above this threshold were ineffective or detrimental under the conditions tested.