Impacts of Chronic Alkalinity Stress on Growth, Physiology, Histology, and Muscle Quality in Qihe Crucian Carp (Carassius carassius)

Saline-alkaline water is increasingly used for aquaculture. Qihe crucian carp (Carassius carassius) is one of the major economic aquacultural species in China; however, the impact of saline-alkaline water on this fish remains unclear. In this study, a 60 d chronic alkalinity stress experiment was conducted to investigate the effects on the growth, physiology, and muscle quality of Qihe crucian carp. One hundred and eighty juvenile fish (31.03 ± 0.71 g) were divided into three treatments (three replicate tanks per treatment, 20 fish per tank): a control group (freshwater), a CA20 group (20 mmol/L), and a CA40 group (40 mmol/L). Despite no effect on survival, alkalinity stress significantly impaired growth performance in both the CA20 and CA40 groups, leading to reductions in final body weight, weight gain rate, and specific growth rate. Similarly, the feed efficiency decreased with increasing alkalinity. Compared to the control group, the alkalinity groups exhibited elevated serum Na+ levels and higher gill Na+/K+-ATPase activity, but reduced Ca2+/Mg2+-ATPase activity. For histology, chronic alkalinity stress induced several changes in the gills, including wider filaments, shortened lamellae, and the increase in interlamellar distance. Regarding muscle nutritional composition, the contents of crude protein and amino acids and the proportions of polyunsaturated fatty acids showed a downward trend with rising alkalinity. Additionally, alkalinity stress significantly decreased muscle fiber density and hardness. Taking into account both growth performance and muscle quality, the suggested aquacultural alkalinity should be controlled below 20 mmol/L for Qihe crucian carp. In conclusion, these findings supported Qihe crucian carp as a promising candidate species for saline-alkaline water aquaculture, providing a scientific basis for the utilization of this special water resource.