The effect of aqueous application of probiotics on growth, heavy metal accumulation, blood biochemistry, and histological alterations of Dicentrarcus labrax

Abstract

High saline groundwater is a potential source for expansion of inland mariculture, especially with increasing freshwater scarcity. This research evaluated the efficacy of using probiotics (EM®) as an aqueous water additive to groundwater on water quality, heavy metal (HM) removal, microbial load, growth performance, and physiological status of European seabass. Four treatments were applied in triplicate using an increasing dose of EM® in water: 0, 0.2, 0.4, and 0.6 mL/L, expressed as EM₀, EM_0.2, EM_0.4, and EM_0.6, respectively. Seabass larvae (0.353 ± 0.002 g/fish) were housed in 1000-L-1 fiberglass tanks (625 fish/tanks) filled with 36 ppt saline groundwater and fed an experimental diet (45.33/14.65, CP/CF) at 10% of their body weight for 60 days. The results showed that the administration of EM® significantly (P < 0.05) improved water quality by reducing total ammonia nitrogen and NH₃ levels as well as increased dissolved oxygen in a dose-dependent manner. Growth indices and feed utilization efficiency were improved in groups reared in EM® treated water. The addition of EM® resulted in a significant decrease (P < 0.05) of HM in culture water, accumulation in muscle and liver of seabass, along with reduction of serum cortisol level. Furthermore, fish in the EM®-treated groups showed a significant improvement in plasma antioxidants (total antioxidant capacity, catalase, and glutathione peroxidase) and immune markers (immunoglobulin, lysozyme) with healthier liver and intestines histological structural compared to the control group. In summary, adding EM® at levels of 0.2–0.4 mL/L can improve saline groundwater criteria, control pathogens and lessen HM accumulation, and improve fish performance and health status.