article · Fish Physiology and Biochemistry
Common carp reared across a range of salinity levels from zero to twenty parts per thousand show clear physiological limits when subjected to saline environments and subsequent heat stress. Fish raised at fifteen and twenty parts per thousand for eight weeks experienced significantly reduced growth, lower feed intake, and impaired feed efficiency, with the poorest outcomes recorded at twenty parts per thousand. Elevated salinity also compromised antioxidant defences in the gills, intestines, and liver, marked by declining levels of superoxide dismutase, catalase, and glutathione peroxidase alongside increased malondialdehyde, an indicator of oxidative stress. Subsequent exposure to thirty-two degrees Celsius for forty-eight hours intensified these negative effects across all tissues, while simultaneously reducing blood immunity markers such as lysozyme activity and nitroblue tetrazolium reduction. Overall, thermal stress exacerbates the physiological disruption caused by hypersaline conditions in this freshwater species.
Environmental fluctuations in temperature and salinity directly impact fish health and productivity. Understanding how common carp respond to combined thermal and saline challenges provides essential baseline knowledge for fish farming operations facing changing water qualities. It reveals the physiological thresholds where stress compromises immune function and feed utilisation, helping managers avoid conditions that undermine fish welfare and yield.
This early-stage experimental research provides biological tolerance thresholds that aquaculture managers and fish farm operators can use to establish water quality guidelines for common carp. While it does not deliver a commercial product, the findings can inform farm site selection, salinity monitoring protocols, and environmental control strategies in warming or brackish environments to protect stock survival and feed efficiency.
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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.
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DOI: 10.1007/s10695-022-01052-w
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