Theses and Dissertations

Date of Award

8-1-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biochemistry and Molecular Biology

First Advisor

MD Saydur Rahman

Second Advisor

Ahmed Touhami

Third Advisor

Arnulfo O. Mar

Abstract

Global climate change has led to rising temperatures, posing significant challenges to aquatic ecosystems and the health of ectothermic species such as goldfish (Carassius auratus) This thesis investigated the effects of heat stress on growth performance, histological alterations, and molecular stress responses in the gill and kidney tissues of goldfish Fish were exposed to control (24°C), medium (28°C), and high (32°C) temperatures for two weeks Growth parameters, including instantaneous growth rate (IGR), absolute growth rate (AGR), body value gain (BVG), and condition factor, were evaluated alongside histological and immunohistochemical markers of stress Results revealed that high temperature significantly reduced AGR in length and condition factor, indicating early signs of physiological stress, while IGR and BVG remained unaffected over the short term Histological analyses demonstrated pronounced structural damage in both organs under heat stress In the gills, high temperatures caused shortened lamellae, irregular inter-lamellar spacing, and reduced mucus secretion, consistent with osmoregulatory and respiratory compromise The kidneys exhibited glomerular atrophy, tubular degeneration, and biphasic changes in melanin content, reflecting oxidative damage and a complex adaptive response Immunohistochemical findings confirmed elevated molecular stress under heat stress Both gill and kidney tissues showed significant upregulation of heat shock protein 70 (HSP70), a key molecular chaperone mitigating protein misfolding Levels of nitrotyrosine-modified proteins (NTP), indicative of nitrosative stress, were also markedly elevated in both tissues, highlighting the contribution of reactive nitrogen species to cellular injury Additionally, reduced Na⁺/K⁺-ATPase expression in gill tissues at high temperature suggested impaired ion transport and osmoregulatory function Together, these findings demonstrate that heat stress impairs growth, damages organ structure, and triggers oxidative and nitrative stress responses in goldfish This study underscores the vulnerability of aquatic organisms to rising temperatures and identifies histological and molecular biomarkers, including HSP70, NTP, and Na⁺/K⁺-ATPase, that can be used to monitor thermal stress These insights contribute to a deeper understanding of climate-induced challenges in aquatic ecosystems and inform management strategies for fish health under warming scenarios.

Comments

Copyright 2025 Ngozichukwu F. Ngozichukwu. All Rights Reserved. https://proquest.com/docview/3275323056

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