Impacts of Salinity on Growth, Physiology and Tissue Integrity of Nile Tilapia: Implications for Coastal Aquaculture Under Climate Change

ABSTRACT Climate change is responsible for salinity intrusion in coastal areas, which is significantly threatening the sustainability of aquaculture. This investigation focused on evaluating growth performance, proximate composition, blood morphology and histopathological modifications in Nile tilapia ( Oreochromis niloticus ) exposed to varying salinity levels. Therefore, this trial was performed with a total of 300 fingerlings exposed to five different triplicated setups (0, 3, 6, 9 and 12 ppt), over 42 days. Salinity concentrations ranging from freshwater to 9 ppt provided favourable conditions, with notable improvements in growth metrics, weight gain (WG), specific growth rate (SGR; %/day) and feed conversion ratio (FCR) for fish. In terms of nutritional profile, Nile tilapia reared at intermediate salinities (3, 6 and 9 ppt) showed elevated protein contents. Furthermore, the glucose level was found to have increased significantly by 12 ppt in comparison with other treatments, while the haemoglobin levels showed an opposite trend, and the prevalence of erythrocytic anomalies (cellular and nuclear) was markedly elevated with increasing salinities. Mild histopathological anomalies in gills (hypertrophy of chloride cells, epithelial lifting, telangiectasia and hyperplasia pillar system distortion), liver (haemorrhage, blood congestion, hypertrophy, the presence of melano‐macrophage centres and haemochromatosis), kidney (haemorrhage, shrinkage of renal corpuscles, necrosis, glomerular damage and occurrence of melano‐macrophage centres) and intestine (beheading of villi, shifting lamina propria, fusion of brush border, degeneration of columnar epithelium and vacuolization of submucosa) were diagnosed in 9 ppt but pronounced anomalies were found at higher salinity (12 ppt). The findings of the current investigation suggest that Nile tilapia is a viable candidate for adaptation to low‐salinity environments, with salinity levels up to 10 ppt.