Diagnostics pla y an important role in aquatic animal health management and disease control . Despite advances in identifying pathogens, the aquaculture sector currently has very limited tools for assessing fish health and is heavily reliant on histopathology; a lethal, labour intensive technique that that does not facilitate rapid fish health assessment. Therefore, t he objective of the work undertaken was to study the use of serum clinical chemistry diagnostic techniques as biomarkers for fish health and welfare. The fish gill is a multi-purpose organ that plays a dominant role in osmotic and ionic control, acid-base regulation and nitrogen waste excretion in addition to promoting gas exchange . Gill disease often has a multifactorial aetiology and a complex histopathological manifestation.
In this particular case, blood biochemistry was used to investigate the clinical significance of complex gill disease (CGD) in aquaculture reared Atlantic salmon to determine relevant blood biomarkers for early diagnostics. Blood was taken from fish with no clinical signs of any pathology (n=30) and from fish with confirmatory clinical appearance of CGD (n=30).
Serum biochemical analysis from CGD fish showed significant increases (p <0.05) in typical markers of excretory dysfunction such as concentrations of ammonia, urea and creatinine . Subsequently, activities of ALP (alkaline phosphatase) , ALT (alanine aminotransferase) and LDH (lactate dehydrogenase) as markers for liver damage and overall health status were increased . Moreover, increased concentrations of minerals such as magnesium and calcium and electrolyte such as chloride indicated impaired osmoregulatory function of gills. Levels of serum iron were significantly decreased suggesting increased red blood cells production caused by low oxygen intake .
In this study the clinical significance of b lood biochemistry was demonstrated as a promising approach to fish heath diagnostics and was correlated with organ/tissue damage. We propose applying th e clinical chemistry approach and expanding it to haematological analysis to facilitate monitoring and early detection of health challenges in salmon aquaculture.