Metabolic and thyroidal response in air-breathing perch (Anabas testudineus) to water-borne kerosene

To address the physiological compensatory adaptations in air-breathing fish to a toxicant, we studied the metabolite pattern, serum and liver enzymes and thyroidal response in a tropical air-breathing perch, Anabas testudineus (kept at 30 °C in a 12-h L:D cycle) after exposing the fish for 48 h to the water-soluble fraction of kerosene. The concentrations of serum glucose (P < 0.05), triglycerides (P < 0.01) and liver total protein (P < 0.05) were significantly increased in kerosene-exposed fish. The serum urea level, however, remained unaffected. A significant (P < 0.05) increase in liver RNA occurred without changing the liver DNA concentration. Kerosene exposure decreased the level of aspartate aminotransferase activities in serum (P < 0.001) and liver (P < 0.05) but it increased (P < 0.05) the liver alanine aminotransferase activity without changing its activity in serum. The levels of serum (P < 0.01) and liver (P < 0.001) lactate dehydrogenase activity were declined and the serum (P < 0.05) and liver (P < 0.05) alkaline phosphatase activity levels were elevated in kerosene-treated fish. The nominated levels (3.33–6.66 ml/L) of kerosene significantly (P < 0.01) elevated the thyroxine (T4) titre, and reduced (P < 0.05) the triiodothyronine (T3) titre. The fish pretreated with either T3 or T4 and exposed to kerosene had a metabolic and thyroidal response that differed from that in control fish treated with kerosene: no rise in serum glucose was observed, nor in triglycerides, total protein and RNA in the liver, whereas declined levels of T4 and T3 were observed. The upregulation of the thyroid along with the marked metabolite changes point to a positive involvement of thyroid in energy metabolism during kerosene exposure. This is consistent with the hypothesis that the fish thyroid responds to the action of petroleum products and influences the metabolic homeostasis of this air-breathing fish.