TOXICITY MODULATION OF CYANOTOXIN NODULARIN IN SHRIMP Litopenaeus vannamei (BOONE, 1931) FED WITH DIETARY AÇAI Euterpe oleracea INCLUSION

Under specific physicochemical conditions of water, dense blooms of Cyanobacteria may occur, including in aquaculture systems. Some of these algae generate secondary metabolites called cyanotoxins (e.g. nodularins), which offering important risks to public health, environment, and productivity of cultured shrimps. Açaí has stimulated interest in the scientific and economic field due to its phytochemical composition, antioxidant, anti-inflammatory and antinociceptive properties. This study evaluated the effect of dietary inclusion of lyophilized açaí Euterpe oleracea (LEO) on  the  redox status of shrimp Litopenaeus vannamei upon exposure at cyanotoxin nodularin (NOD) in bioflocs system.

For 30 days, three hundred shrimp juveniles (1.5 ± 0.39 g) were randomly divided into two groups (six tanks of 100 L; 50 shrimp/tank)  (25% salinity, pH 8, 28 °C, 12C/12D photoperiod) and fed twice a day with two diets: one containing 0.00 (control diet) and  the other 10.0% LEO (w/w). After feeding period, both shrimp groups were submitted to three treatments (14L; 7 shrimp/tank) with different concentrations of cyanotoxin NOD (0.00; 0.25; and 1.00 μg/L) dissolved in water by 96h of exposure. At the end of the exposure, shrimp were sampled (n= 15/treatment) for the determination of reduced glutathione (GSH), the activity of glutathione-S-transferase (GST), sulfhydryl groups associated at proteins (P-SH), and lipid peroxidation (TBARS) in the hepatopancreas, gills, and muscle. The NOD accumulation was measured in muscle.

The results showed that dietary LEO significantly increased GSH levels (p<0.05) in the hepatopancreas and gills of the shrimps exposed to NOD. Toxin exposure did not modify GST activity in all organs (p>0.05). Levels of lipid peroxidation in the muscle were lower ( p<0.05) in the shrimp fed with the LEO diet and exposed to NOD. The shrimp LEO-fed showed a lower means of P-SH level in the muscle (p<0.05). Finally, NOD toxin did not accumulate in muscle but, notably was detected in control groups fed or not with dietary LEO (Fig. 1 ). Açaí per se was able to induce the antioxidant system of the L. vannamei, as well as lower the TBARS levels ( p<0.05) in the muscle of the shrimps exposed to nodularin, indicating that dietary LEO has chemoprotective potential.

Thus, supplementation with açaí was able to induce antioxidant defenses to attenuate the deleterious effects caused by exposure to NOD and, supposedly, induced a hormetic response that promoted the lowering in the muscle TBARS levels when shrimps were exposed to low nodularin concentrations. Accumulated nodularin in the muscle of control shrimps is a case of a concern, indicating previous exposure to this toxin in the rearing tanks, a finding that needs further studies to understand their potential impact in BFT systems.