以大穗型杂交中稻蓉18优1015和多穗型杂交中稻内6优103为材料，于2018年在四川泸县开展试验，研究稻鱼共生模式下不同施氮量（N0，不施氮；N1，减氮66.6%；N2，减氮33.3%；CK，常规施氮，施氮量135 kg/hm2）对杂交中稻产量、产量构成因子、干物质、收获指数、氮肥利用率的影响。结果表明，大穗型杂交中稻产量以N2处理最高，较CK增加2.8%；多穗型杂交中稻产量以CK最高，较N2、N1处理分别增加5.3%、20.4%；随施氮量的增加，杂交中稻有效穗数、干物质量呈显著增加的趋势，结实率、收获指数则呈下降趋势，减量施氮对杂交中稻每穗粒数和千粒重影响不显著；大穗型杂交中稻的氮肥农学利用率N2、N1处理较CK分别增加63.2%、45.6%，多穗型杂交中稻氮肥农学利用率N2处理较CK增加了27.4%；随施氮量的增加，杂交中稻氮肥偏生产力呈显著下降趋势，与CK相比，N2、N1处理的氮肥偏生产力分别增加了74.6%和48.2%。可见，在稻田养鱼模式下，综合考虑产量和氮肥利用率，杂交中稻的适宜减氮量为33.3%。

A field experiment was conducted to study the effects of nitrogen application rate （N0, without N; N1, a reduction in nitrogen application rate by 66.6%; N2, a reduction in nitrogen application rate by 33.3%; CK, conventional nitrogen application, nitrogen application rate was 135 kg/hm2） on grain yield, yield components, dry matter weight, harvest index and N use efficiency （NUE） of mid-season hybrid rice under rice-fish system, using two mid-season hybrid rice cultivars （Rong 18 you 1015 with large panicle, Nei 6 you 103 with more panicles） as materials. The results showed that, for the large panicle mid-season hybrid rice, the N2 treatment recorded the highest grain yield, which was 2.8% higher than CK; for the more panicles mid-season hybrid rice, the CK recorded the highest grain yield, which was 5.3% and 20.4% higher than N2 and N1 treatment, respectively. The effective panicles and dry matter weight of mid-season hybrid rice increased with the increase of N application rate; while the seed setting rate and harvest index of mid-season hybrid rice decreased with the increased of N application rate. There was no significantly difference in spikelets per panicle and thousand grain weight among the four treatments. For the large panicle mid-season hybrid rice, the agronomic efficiency of nitrogen fertilizer in N2 and N1 treatment increased by 63.2% and 45.6%, respectively, compared with CK; for the more panicle mid-season hybrid rice, the agronomic efficiency of nitrogen fertilizer in N2 treatment increased by 27.4% , compared with CK. With the increase of N application rate, the partial factor productivity of applied N of mid-season hybrid rice showed a significant decline. Compared with CK,  the partial nitrogen productivity of N2 and N1 treatment increased by 74.6% and 48.2% respectively. Under the rice-fish system, the optimum nitrogen reduction rate of hybrid rice was 33.3% considering the yield and nitrogen use efficiency.