Abstract
Aquaculture activity is affected by various environmental factors, including water salinity and high temperatures. The present study investigated the impact of using varying water salinity (0, 5, 10, 15 and 20 ppt) on the growth behavior, immune responses and antioxidative responses of common carp. Fish were raised under optimal conditions except for water salinity for 8 weeks; fish were then subjected to high-temperature stress (32 °C) for 48 h. The results indicated a reduced final weight (FBW), weight gain (WG), specific growth rate (SGR), condition factor (CF), feed intake and feed efficiency ratio (FER) in common carp reared in 15 and 20 ppt (p < 0.05). The lowest FBW, WG, SGR, CF, feed intake and FER values were observed in fish reared in 20 ppt water salinity (p < 0.05). In gills, the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were markedly decreased, but malondialdehyde (MDA) levels increased in fish challenged with 15 and 20 ppt before they were subjected to heat stress (p < 0.05). After heat stress, the SOD, CAT and GPx were decreased, and the MDA increased in fish reared in varying salinity levels (p < 0.05). Before heat stress, the intestinal SOD, CAT and GPx markers were decreased by 15 and 20 ppt, while the MDA level was increased by 15 and 20 ppt (p < 0.05). Generally, heat stress lowered the SOD, CAT and GPx activity in the intestines and liver tissues but increased MDA levels in common carp stressed by varying salinity levels (p < 0.05). The most decreased lysozyme activity, SOD, CAT and GPx and increased MDA levels were observed in common carp exposed to 20 ppt before and after heat stress (p < 0.05). After heat stress, fish exposed to 15 and 20 ppt had lower NBT than the remaining groups, and fish exposed to 20 ppt had the lowest values (p < 0.05). Overall, the heat stress markedly suppressed the antioxidant and immune responses of common carp reared in hypersalinity conditions.
Highlights
Climatic changes are the primary reason for unstable environmental conditions in the aquaculture sector (Zarantoniello et al, 2021)
The final body weight (FBW), weight gain (WG) and specific growth rate (SGR) were all significantly reduced in fish reared in 15 and 20 ppt compared with fish grown in 0 and 5 ppt (p < 0.05)
Fish reared in 10 ppt water salinity had no significant differences for FBW, WG and SGR relative to fish reared in 0 and 5 ppt (p 0.05) (Table 1)
Summary
Climatic changes are the primary reason for unstable environmental conditions in the aquaculture sector (Zarantoniello et al, 2021). The ecosystem is replete with components which have been directly impacted by climatic changes, such as water salinity and temperature (Imsland et al, 2003; Kim et al, 2017). Rivers and lakes are the major sources of water for fish farms, but increased temperatures have caused a high evaporation rate, especially during the summertime (Chang et al, 2021). The level of water salinity has increased, leading to decreasing oxygen saturation and impacting osmoregulation (Dawood et al, 2020a, 2020c). Hypersalinity results in increased osmoregulation demands to adapt to stressful conditions that consume high energy levels, causing low feed consumption and growth rates (Saravanan et al, 2018; Tang et al, 2020). Several reports have investigated the impacts of hypersalinity on the performance of common carp (Naskar et al, 2021; Salati et al, 2011)
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