Abstract
Naked carp (Gymnocypris przewalskii), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combinations of high salinity and alkalinity, but migrate to spawn in freshwater rivers each year. In this study, we measured the drinking rate over a 24 h period for naked carp exposed to saline-alkaline lake waters with salinities of 15 (L15) and 17 (L17). We also assessed the daily feed intakes of naked carp exposed to L15 and fresh water (FW). Additionally, we studied the daily expression of acid–base regulation and osmoregulation related genes and proteins in the intestine of naked carp exposed to saline-alkaline lake waters. Our results revealed that the drinking rate at night was significantly higher than in daytime when exposed to either L15 or L17, while feed intakes in daytime were significantly higher than at night. The relative expression of Na+/K+-ATPase α (NKA-α), solute carrier family members 26A6 (SLC26A6) and 4A4 (SLC4A4) in the intestine of naked carp exposed to L17 at night was higher than in daytime. Specifically, NKA-α mRNA expression at 4:00 was 7.22-fold and 5.63-fold higher than that at 10:00 and 16:00, respectively, and the expression at 22:00 was 11.29-fold and 8.80-fold higher than that at 10:00 and 16:00, respectively. Similarly, SLC26A6 mRNA expression was greatest at 22:00, exceeding that observed at 4:00, 10:00 and 16:00 by 3.59, 4.44 and 11.14-fold, respectively. Finally, the expression of NKA-α and SLC26A6 protein at the single cell level was also higher at night than during the day, which was 1.65-fold and 1.37-fold higher at 22:00 respectively compared to 16:00. Overall, the present findings revealed that naked carp drinks at night and feeds during the day, demonstrating that intestinal ion regulation exhibits a daily rhythm when exposed to high saline and alkaline lake water.
Highlights
Naked carp (Gymnocypris przewalskii), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combinations of high salinity and alkalinity, but migrate to spawn in freshwater rivers each year
We measured the daily feed intakes of naked carp exposed to saline-alkaline lake water (L15) and fresh water (FW).We studied the daily expression of genes and proteins, which related to acid–base regulation and osmoregulation, in the intestine of naked carp exposed to saline-alkaline lake waters
Considering that the naked carp lacks a stomach for physically partitioning digestion and absorption, we hypothesized that these fish might partition these functions temporally when moving into the hyperosmotic lake water
Summary
Naked carp (Gymnocypris przewalskii), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combinations of high salinity and alkalinity, but migrate to spawn in freshwater rivers each year. We measured the drinking rate over a 24 h period for naked carp exposed to salinealkaline lake waters with salinities of 15 (L15) and 17 (L17). We studied the daily expression of acid– base regulation and osmoregulation related genes and proteins in the intestine of naked carp exposed to saline-alkaline lake waters. The present findings revealed that naked carp drinks at night and feeds during the day, demonstrating that intestinal ion regulation exhibits a daily rhythm when exposed to high saline and alkaline lake water. Additional research has shown that the digestive and drinking behavior of fish in general cannot be performed at the same t ime[8] This led us to question, whether a stomachless fish, such as naked carp might partition these functions temporally rather than physically
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