Molecular characterisation of HSP70 gene expression, histopathology and immune system of snakehead fish, Channa striata, under temperature and bacterial stress / Ihlam Ibrahim Eid Elhussein

Ihlam Ibrahim, Eid Elhussein (2020) Molecular characterisation of HSP70 gene expression, histopathology and immune system of snakehead fish, Channa striata, under temperature and bacterial stress / Ihlam Ibrahim Eid Elhussein. PhD thesis, Universiti Malaya.

	PDF (The Candidate's Agreement) Restricted to Repository staff only Download (132Kb)
	PDF (Thesis PhD) Download (1235Kb)

Abstract

Snakeheads are air-breathing freshwater fishes containing two genera, Channa (Asia) and Parachanna (Africa). The Asian genus is dominated by Channa striata which is found in southern and Southeastern parts of the continent. In this research, environmental and bacteria stressor to Channa striata were investigated. HSP70 gene was studied as an environmental stress gene (ChHSP70). Results showed a cDNA sequence of the gene to be (~918bp). It was also shown the gene is highly similar to that of other fish species. Constructing a phylogenetic tree of the gene across vertebrate species revealed six main clusters; same class remained conserved by showing high sequence similarity except for fish which showed two groups. One possible reason for this diversity might be the gradual global warming. Of the two fish groups, polymorphism was found to be higher in one of them, indicating clear bias in their mutation rates, which may result in new speciation. The clear separation between the two fish groups also suggests presence of undiscovered functional differences. Genes that are phylogenetically stable have conserved their core functions, while those that display a much more varied or unstable phylogeny have much more varied functions. This diversity in fish species may be due to the environmental adaptation of this gene to environmental stresses that are more pronounced for aquatic organisms than higher, terrestrial vertebrates. HSP70 expression has been shown to be stimulated by a wide variety of physiological and environmental stresses, including thermal shock, heavy metals, free radicals and microbial infection. Responses of HSP gene can vary according to tissue, HSP family, and stressors. The sensitivity of HSP gene expression can also vary according to species, developmental stage and season. Higher expression levels of HSP70 due to thermal stress indicates better tolerance to heat stress. In this study the expression of the gene at 32°C in the stomach and fin was higher than that of the gills. The study showed the sustainability of C. striata in term of hydrologic regime and global warming might cause mortality or even extinction of this fish. Another factor that may have affected the survival of this fish was bacterial disease. A strain of bacteria was isolated from an infected fish. Identification of the bacterium was based on 16S rRNA gene sequence of 1160bp which showed the closest match to Enterobacter soli strain LF7a (99.31% similarity). The sequences obtained designated as Enterobacter soli Es2. The current study is the first to report Enterobacter soli Es2 as a disease causative agent in fish. The main clinical signs of the disease were skin ulcer, dullness, loss of appetite and abnormal swimming behavior. Histopathologically, hepatic lesions including blood congestion were observed. The latter hinders blood movement from the hepatic portal vein and hepatic artery into the central vein resulting in dilation of sinusoids and rupture of blood vessels. Moreover, expression of galectin 8 (CsGale), glutathioneS-transferase (CsGlut), h2Calponin (CsCalp) and cytochromeb5 (CsCyto) genes, which are known as immune-related genes, were tested after challenging the fish with Enterobacter soli Es2. The tested genes showed different Patterns of expression in different tissue types.

Actions (For repository staff only : Login required)