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The rare and endemic largemouth bronze gudgeon (Coreius guichenoti) inhabits the middle and upper reaches of the Yangtze River. It is a typical migratory river fish found in the vicinity of rapids. Over the years, the construction of water conservancy facilities and overfishing by humans have harmed the ecological habitat of this species, resulting in a considerable population decline. Thus, the largemouth bronze gudgeon has emerged as an important conservation objective and artificial stocking target for protecting and restoring the ecological environment in the Yangtze River Basin. Artificial stocking is one of the most effective methods for restoring the population of rare and endangered fish, and it is widely used domestically and abroad. Culturing a healthy and sufficient number of fry is critical to stocking success. In the production of largemouth bronze gudgeon, the formulation of an effective feeding strategy plays an important role. A scientific and reasonable feeding rate and frequency serve as guidelines for improving the production and quality of cultured fry, which directly impact the survival rate, growth performance, and feed consumption of fish. In order to determine the appropriate feeding strategy for improving fry breeding efficiency, an 8-week feeding trial in a 5 × 2 two-factorial design was conducted to investigate the effects of feeding levels (1%, 2%, 3%, 4%, and 5%) and feeding frequency (2 and 3 times/d) on growth, whole-body composition, digestive enzyme activity, and liver structure of juvenile largemouth bronze gudgeons with an initial weight of (4.91±0.11) g. The results were as follows: After 8 weeks of culture, the survival status of largemouth bronze gudgeon in each treatment group was good. Only two fish mortalities were observed, one in each of the two feeding frequency groups at the 5% feeding level. There was no mortality in the other groups. Feeding level, feeding frequency, and the interaction of the two items had significant effects on the weight gain rate (WGR), specific growth rate (SGR), and feed efficiency (FE) of individuals, whereas only the feeding frequency had significant effects on the condition factor (CF) and viscerosomatic index (VSI). WGR and SGR significantly increased with the feeding level. Meanwhile, the FE increased with increasing feeding levels and then stabilized at the 3% feeding level. Fish fed 3 times/d had higher WGR, SGR, and FE than fish fed 2 times/d when feeding levels did not exceed 3%. As feeding frequency increased, the CF and VSI of individuals tended to decrease. Both whole-body moisture content and crude fat content were significantly affected by the feeding level. The increase in feeding level decreased the whole-body moisture content while increasing the whole-body crude fat content. Digestive enzymes in the foregut of individuals were not significantly affected by feeding level, feeding frequency, or their interactions; however, the feeding level had significant effects on hepatic trypsin (TPS) and lipase (LPS) activities. Increasing feeding levels considerably reduced the TPS activity when the feeding levels were higher than 3%, whereas the LPS activity initially increased and then decreased with increasing feeding levels at a feeding frequency of 3 times/d. Hepatic HE staining revealed that the hepatocytes of fish fed 2 times/d continued to increase in size and progressively swelled and vacuolated, exhibiting indications of a fatty liver when the feeding level reached 3% and increased further. Hepatocytes of fish fed 3 times/d were surrounded by a large number of round and ovoid lipid droplets at the 3% and 4% feeding levels, but there were no discernible changes in the structure of the cells. When the feeding level reached 5%, hepatocytes began to enlarge and swell in groups at a feeding frequency of 3 times/d, but to a lesser extent than the groups fed 2 times/d. In conclusion, under the conditions of this experiment, a comprehensive assessment of growth performance, feed utilization efficiency, and hepatic health revealed that feeding juvenile largemouth bronze gudgeons three times daily at a level of 3% body weight was the optimal feeding strategy. The objective of this study was to determine the optimal feeding strategy for the fry culturing process. The findings provide theoretical guidelines for the artificial reproduction of largemouth bronze gudgeon and contribute to the recovery of its native population. Additionally, as a species that inhabits torrential habitats, the largemouth bronze gudgeon possesses distinct digestive and physiological properties. This study lays the foundation and groundwork for future research on the nutritional requirements, feed production, and artificial breeding of these species. |
