Effects of Bacillus subtilis-fermented rice bran on water quality, performance, antioxidants/oxidants, and immunity biomarkers of White leg shrimp (Litopenaeus vannamei) reared at different salinities with zero water exchange

The current study was carried out to assess the effects of using Bacillus subtilis-fermented rice bran (FRB) on water quality parameters, water microbial counts, growth performance, body composition, antioxidants/oxidants, and immunity biomarkers of white leg shrimp (Litopenaeus vannamei) reared at different salinities. Shrimp juveniles (0.51 +/- 0.11 g) were distributed in triplicates into 27 1-m(3) fiberglass tanks (1,000 animals/m(3)/each) and subjected to bifactorial treatments (three feeding types using FRB with three different salinity levels). After acclimation to different salinities (5, 15, and 35 g/L), under each salinity level shrimps received a 40% protein-commercial diet (100 CD) only, 50% commercial diet plus FRB (50 CD+FRB), or FRB only for 12 weeks. A half of each tank's water in the 100 CD groups was replaced daily with new water containing the same salinity level; no water exchange was done in the other two groups. Total ammonia-nitrogen, pH, and nitrite values of water in 50 CD+FRB and FRB tanks were significantly lower than those in 100 CD tanks (P < 0.05). The total bacterial and Bacillus sp. counts in the water of the 50 CD+FRB and FRB tanks were significantly higher; Vibrio sp. counts were significantly lower than the 100 CD treatment especially at 35 g/L salinity. The growth and yield of shrimp were significantly higher in tanks that received FRB only at a salinity of 35 g/L with zero water exchange. Interestingly, significant increases in crude protein, total lipids, and ash contents in the flesh of shrimp that received FRB only at 35 g/L salinity were observed. Furthermore, feeding type and/or water salinity significantly modulated antioxidants/oxidants (malondialdehyde [MDA], superoxide dismutase [SOD], and catalase [CAT]) and immune biomarkers (lysozyme [LYZ] and phenol oxidase [PO]). It is noted that antioxidants/oxidants significantly decreased as salinity levels increased, especially in tanks that received FRB only. Immune biomarkers were significantly higher in animals reared in FRB-based tanks than those that received artificial feeding. Their activities also significantly increased as salinity levels increased. Overall, the application of FRB in shrimp culture at 35 g/L salinity with zero water exchange could sustain considerably better growth and yield of white leg shrimp by saving feed supplementation and subsequently reducing the feeding cost.