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

Abstract

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-m3 fiberglass tanks (1,000 animals/m3/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.