Background and Aim: Industrial waste, such as heavy metals, is a major source of water pollution; at high levels, such pollution can reduce river water quality to the extent that it becomes unsuitable for aquaculture of freshwater fish. This study aimed to focus on the effects of copper (Cu) exposure in Nile tilapia (Oreochromis niloticus) and specifically the ability of Lactobacillus-based probiotics supplementation in fish feed to ameliorate damage to gonads and negative effects on red blood cells (RBCs), whole blood cells (WBCs), hematocrit (HCT) levels, hemoglobin (HGB) levels, and malondialdehyde (MDA) levels following such exposure.

Materials and Methods: Thirty-two Nile tilapia fish were divided into eight groups: A negative control (without probiotics or Cu), a positive control (with probiotics but without Cu), three treatments with probiotics in feed, and one of three Cu concentrations (0.75, 1.50, or 3.00 mg/L), and three treatments with these three Cu concentrations but without probiotics in feed. The probiotics concentration in feed was 25 mL/kg (1×10⁸ CFU/mL). Feeding was for 15 days, after which the hematological parameters, gonadal (testis) structure, and MDA levels of fish were analyzed.

Results: Exposure to Cu significantly (p<0.05) affected fish hematology (decreased HGB, HCT, RBC, and WBC levels) and altered the structure of the testes. However, the addition of probiotics to fish feed significantly (p<0.05) ameliorated these effects on hematology and maintained the histological structure of the gonads.

Conclusion: Cu exposure at ≥1.5 mg/L affected the hematologic parameters, gonadosomatic index, MDA levels, and testicular cells and tissue of Nile tilapia. However, probiotics supplementation in fish feed helped ameliorate the negative effects of Cu on these parameters. Thus, the Lactobacillus-based probiotics used in this study were apparently able to neutralize Cu toxicity in Nile tilapia.

Keywords: copper, fisheries, fresh water, hematology, probiotics, testis structure.