Administration of purple nonsulfur bacteria as single cell protein by mixing with shrimp feed to enhance growth, immune response and survival in white shrimp (Litopenaeus vannamei) cultivation

Single cell protein (SCP) is an alternative way to increase nutrients for animal consumption; and purple nonsulfur bacteria (PNSB) should be considered as SCP due to their rich sources of protein, vitamins and photopigments. Hence, the aim of this study was to investigate the potential of promising PNSB to be used as SCP by mixing with commercial shrimp feed for white shrimp cultivation starting from postlarval until early juvenile stages for 60 days. PNSB strains, Rhodobacter sphaeroides SS15 and Afifella marina STW181 were selected, based on high amounts of biologically complete protein and photopigments, to use as SCP at a ratio of 1: 1; and their lyophilized cells at 1, 3 and 5% (w/w) were mixed well with commercial shrimp feed to obtain modified shrimp feed recipes; Diet 1, Diet 2 and Diet 3, respectively. Levels of NH4+, NO2-, NO3- and COD in rearing water from Diet 2 and 3 sets were significantly higher than control set. However, Diet 1 set showed the lowest levels of these water parameters among modified diet sets as no significant difference levels of NO3- and COD between Diet 1 and control sets. Shrimp growth performance on the basis of relative gain rate and other growth parameters found that Diet 1 set was much better than sets of Diet 2, Diet 3 and control with the lowest found in the control set. In addition, the maximum shrimp survival was observed in Diet 1 set (85%) although no significant difference among them as 80% in control set. No significant difference was found among control and all modified shrimp diets for total hemocyte count in shrimp; however, significant increases of superoxide dismutase activity found in sets of Diet 1, while phenoloxidase activity found in Diet 2 and Diet 3. The results of hepatopancreas (HP) histopathology analysis also showed a good condition of HP as healthy shrimp. PNSB biomass as SCP at optimal level has the potential to be an effective source of a novel protein in shrimp feed to enhance shrimp growth and also to increase shrimp survival as more nutritious with no effect on water quality.