Self feeding Rhythm and Growth Characteristics of Gymnocypris przewalskii

Abstract

The total saline-alkaline land area in China is about 99.13 million hectares distributed across northern China, coastal areas, and areas along the bank of the Huanghe River. About 46 million hectares of saline-alkaline water areas are distributed around these saline-alkaline lands, most of which are thalassic and characterized by a high pH value in excess of 8.8 associated with high-carbonate alkalinity concentrations and various types of ion imbalances. Saline-alkaline waters are stressful environments in which only relatively few organisms are able to survive. Consequently, most of the saline-alkaline water resources have been desolate for a long time. The effective utilization of saline-alkaline water resources will benefit restoration of saline-alkaline habitats and the expansion of aquaculture space. Naked carp (Gymnocypris przewalskii) are endemic to the austere saline-alkaline environment of Qinghai Lake. Due to overfishing in the 1960s and environmental changes in the lake area, the resources necessary for naked carp survival in Qinghai Lake declined substantially. At present, the major measures to protect the naked carp and maintain the ecological balance of Qinghai Lake are through a fishing ban and artificial stocking and releasing. The feeding behavior of fish under natural conditions has obvious rhythm characteristics, which is an important research topic for healthy aquaculture. To explore the characteristics of self-feeding rhythm and growth performance of fish in a saline-alkaline environment and provide basic data for the protection of native saline-alkaline fish, naked carp were taken as representative in this study. First, the freshwater and lake water group with natural photoperiod (14L: 10D) and the lake water group with darkness (24D) were set. The artificial lake water was prepared according to the ionic composition of Qinghai Lake, with the contents of Na+ 23.05%, K+ 1.34%, Ca2+ 0.11%, Mg2+ 6.88%, HCO3– 7.09%, CO32– 5.07%, Cl– 40.39%, and SO42– 16.07%. The measured salinity of the artificial lake water was 15.08, and the carbonate alkalinity was 27.53 mmol/L. According to the local photoperiod of Qinghai Province, the whole day was divided into five periods as 05:00–08:00, 8:00–11:00, 11:00–15:00, 15:00–19:00, and 19:00–05:00. The feeding rhythm experiment lasted for 5 d, and the average food intake of each period was calculated. The results showed that naked carp had an obvious daily feeding rhythm during their natural photoperiod. In the natural photoperiod, the feeding peak was from 08:00 to 11:00, and the low feeding period was from 05:00 to 08:00 in freshwater. In the lake water, naked carp showed high and continuous feeding from 08:00 to 19:00, and their average hourly feed intake was significantly higher than that from 05:00 to 08:00 and 19:00 to 05:00. Therefore, naked carp were determined to be the daytime feeding fish type. In addition, the high proportion and the continuous feeding in daytime in lake water indicated that the osmotic and acid-base regulation of naked carp in saline-alkaline water may enhance their diurnal feeding rhythm. Whereas in the continuous dark environment, the feeding rhythm of naked carp was weakened, and the average hourly food intake of each period was similar. To explore the growth performance of naked carp under a self-feeding rhythm, the lake water group and the freshwater control group with natural photoperiod were set up. After 63 days of self-feeding, the individual body length and weight of the naked carp were measured after being anesthetized with MS-222. The length growth rate (1.19±0.17)%, weight growth rate (10.66±0.98)%, and specific growth rate (0.16±0.02)%/d of naked carp in the lake water group were significantly lower than those in the freshwater group [length growth rate (18.66±0.41)%, weight growth rate (67.32±3.05)%, and specific growth rate (0.82±0.03)%/d)], indicating that the growth of naked carp was inhibited by high salinity and carbonate alkalinity environment. The parameter b of body length-weight relationship curve of the naked carp in both the lake water group and the freshwater group was less than three, which showed that the naked carp was a negative allometric growth fish. The b value of the lake water group was lower than that of the freshwater group, and the body length of naked carp increased faster than body weight in the lake water. The growth characteristics of naked carp were affected by the high saline-alkaline environment. The self-feeding rhythm and growth performance of naked carp provided a basic knowledge for creating a feeding strategy for fish cultured in a saline-alkaline environment and recovering endangered native saline-alkaline fish.

Keywords

• saline-alkaline environment
• gymnocypris przewalskii
• self feeding rhythm
• growth performance