The ability of dietary essential oils to mitigate nickel-induced growth retardation, immune-antioxidant suppression, and endoplasmic reticulum stress activation in Nile tilapia.

Abstract

Fish immunity is significantly impacted by waterborne metal intoxication. Nickel is a ubiquitous metal in aquatic bodies which badly impacts fish immune responses and survival. In the current research, we looked into the possible protective effects of essential oils of tea tree (TTO) and basil (BEO) against nickel exposure in Nile tilapia, or Oreochromis niloticus. To achieve this, 240 Nile tilapia (27.92 ± 0.22 g) were categorized into six groups for 45 days; three groups were fed on basal control, TTO, and BEO diets without Ni exposure. The other three groups were subjected to Ni at a level of 3.6 mg/L and fed on basal, TTO, and BEO diets. The outcomes showed a substantial decrease in the growth measures and survival % in the Ni-exposed fish. Oxidative stress (higher splenic malondialdehyde and lower splenic catalase, reduced glutathione, and superoxide dismutase), immune suppression (lower serum lysozyme, myeloperoxidase, and nitric oxide), and elevated serum cortisol levels were observed in the Ni-intoxicated group. The Ni-intoxicated group exhibited various pathological alterations detected in the intestinal tissue mainly inflammatory and necrotic changes, moreover, moderate depletion of lymphoid elements represented by necrotic lymphocytes in the splenic tissue. Ni-exposure induced endoplasmic reticulum stress through up-regulation of the splenic expression of protein kinase R-like endoplasmic reticulum kinase, activating transcription factor 6, CCAAT/enhancer-binding protein homologous protein, X-box binding protein 1, α-subunit of eukaryotic initiation factor 2, inositol-requiring kinase 1a, mitogen-activated protein kinase, c-JunN-terminal kinase, and binding protein for immunoglobulins. Feeding on the TTO and BEO diets improved the growth measures, survival, and antioxidant capacity. Immunomodulation, enhancement of the intestinal and splenic architecture, and relief of the endoplasmic reticulum stress condition were noticed when the Ni-intoxicant groups were fed on TTO and BEO diets. Overall, the effect of the TTO diet was more pronounced than the BEO diet in mitigating the negative consequences of Ni-intoxication in Nile tilapia. Dietary fortification of 0.1% TTO and/or 0.1% BEO is recommended during Ni exposure in aquaculture practices.