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V. S. Peter ¹, M. C. S. Peter ²

Affiliations
1 Department of Zoology, Fatima Mata National College, Kollam 691001, Kerala, IN
2 Department of Zoology, University of Kerala, Kariavattom 695581, Thiruvananthapuram, Kerala, IN

Abstract

To understand the physiological mechanism of stress tolerance in fish living in coconut husk retting grounds, we examined the metabolic pattern, and interrenal and thyroidal activities in the air-breathing perch, Anabas testudineus after exposing them to the effluent of coconut husk retting (CHRE). Cortisol, the end product of interrenal axis and triiodothyronine (T₃) and thyroxine (T₄), the primary hormones of thyroid, were measured in the plasma of these fish together with the indices of metabolic regulation. Five days of CHRE exposure increased the plasma cortisol but decreased the plasma T₄ without affecting the plasma T₃. The concentration of plasma glucose, triglycerides and urea were significantly increased in the CHRE-exposed fish. Significant reduction in the concentration of liver total protein, RNA and DNA occurred in the CHRE-treated fish. CHRE treatment, while increasing the alanine aminotransferase and alkaline phosphatase activities, decreased the aspartate aminotransferase activity in the liver. Besides identifying plasma glucose and cortisol as reliable biomarkers of CHRE-induced stress, our results suggest that these fish reallocate their energy resources during stress where both interrenal and thyroid glands have roles to play.

Keywords

Teleost Fish, Stress, Thyroid Hormones, Intermediary Metabolism, Coconut Husk Retting.

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J. Leji ¹, G. S. Babitha ², V. Rejitha ¹, A. S. Vijayasree ¹, J. Ignatius ², V. S. Peter ², O. V. Oommen ¹, M. C. S. Peter ¹

Affiliations
1 Department of Zoology, University of Kerala, Kariavattom, Thiruvananthapuram 695581, Kerala, IN
2 Department of Zoology, Fatima Mata National College, Kollam 695001, Kerala, IN

Abstract

The coconut husk retting in the backwaters of Kerala in Southern India, releases toxic effluents (CHRE), which pose a threat to the life of many inhabitants including fish. The indices of osmoregulatory activity and the levels of plasma triiodothyronine (T₃) and thyroxine (T₄) in the Mozambique tilapia Oreochromis mossambicus were quantified after exposing them to the effluents to understand the physiological mechanism of tolerance. The plasma glucose, an indicator of catecholamine secretion, remained unchanged in the tilapia exposed to CHRE. The plasma T₄ significantly increased in the tilapia kept in CHRE-rich water, though it declined in the fish kept for recovery in lake water. The plasma K⁺ significantly decreased in the tilapia treated with CHRE, which returned to the basal levels in those kept for recovery. The Na⁺, Ca²⁺ and PO₄^3- remained the same in both treated and untreated fish. The branchial Na⁺, K⁺-ATPase activity increased in the CHRE-exposed fish, and such an effect was not reversed in the recovery group. The renal Na⁺, K⁺-ATPase activity decreased in the lake water-exposed tilapia but not in the CHRE-treated fish. A reversal in the renal Na⁺, K⁺-ATPase activity was obtained in the tilapia kept for recovery in lake water. The intestinal Na⁺, K⁺-ATPase activity significantly declined in the CHRE-exposed tilapia but not in the recovery group. The data indicate that the presence of CHRE in lake water affects the osmoregulatory potential of tilapia without influencing their metabolic status. The up-regulated thyroid activity in the CHRE-exposed tilapia points to its involvement in the ion homeostasis during CHRE intoxication.

Keywords

Coconut Husk Retting, Fish, Metabolism, Oreochromis mossambicus, Stress, Thyroid Hormones, Tilapia.

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