投喂策略对圆口铜鱼幼鱼生长、消化酶及肝脏组织结构的影响

为探究圆口铜鱼(Coreius guichienoti)苗种培育的适宜投喂策略，实验采用5×2双因子设计，通过8周的养殖投喂，研究投喂水平(1%、2%、3%、4%和5%)和投喂频率(2和3次/d)对圆口铜鱼幼鱼初体重(4.91±0.11) g]生长、体成分组成、消化酶活性和肝脏组织结构的影响。结果显示，随着投喂水平的增加，圆口铜鱼的增重率和特定生长率显著增加，饲料效率随着投喂水平的增加而递增，但在投喂水平达到3%后趋于平稳。鱼体肥满度和脏体比随投喂频率的增加有降低的趋势，当投喂水平不超过3%时，3次/d投喂组的增重率、特定生长率和饲料效率均显著高于2次/d组。全鱼的粗脂肪含量随投喂水平的增加而增加，而全鱼的水分则显著下降。投喂水平对肝脏胰蛋白酶和脂肪酶具有显著影响，当投喂水平超过3%时，投喂水平升高显著降低了肝脏胰蛋白酶的活性，而在3次/d投喂组，肝脂肪酶随投喂水平增加呈先增加后下降的趋势。投喂水平、投喂频率以及二者的交互作用对圆口铜鱼前肠消化酶均无显著影响。随着投喂水平的增加，圆口铜鱼肝脏脂肪蓄积逐渐增多，并诱发脂肪肝，且在同一投喂水平下，3次/d组的脂肪肝症状较2次/d组的症状轻...

Effects of feeding strategy on growth, digestive enzymes, and liver structure in juvenile Coreius guichienoti

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.