Spatial niche of major fishes in Qingshitan Reservoir

【Objective】 To elucidate and study interspecies relationship between the main fishes competing spatially in the Qingshitan Reservoir, clarify the correlation between the main fishes and environmental factors, and provide a reference basis for the water environment management and fishery resources protection and sustainable utilization in the Qingshitan Reservoir.【Method】 Based on data of fishery resources survey in the Qingshitan Reservoir in July 2020(flood season) and January 2021(dry season), the index of relative importance(IRI) was used to determine the importance of various fishes. Spatial niche breadth(B_ij) and niche overlap(Q_ij) of major fishes were examined using the mean crowding (x^*), Shannon, and Pianka indexes, and correlation between fish communities and environmental factors was explored by redundancy analysis(RDA) and detrended correspondence analysis(DCA).【Result】 In flood season and dry season of Qingshitan Reservoir, there were 16 and 13 major fish species, respectively. In flood season, dominant species were Rhodeus ocellatus, Hemiculter leucisculus, Coptodon zillii, Sinipercas cherzeri and Oreochromis niloticus;in dry season, the dominant species were Carassius auratus, Opsariichthys bidens, Rhodeus ocellatus, S. cherzeri and Cyprinus carpio. Niche breadth of major fish species in flood season and dry season were 0.11-1.58 and 0.04-1.64, respectively. C. zillii was the wide-niche species(B_ij ≥ 2.0) in flood season, and H. leucisculus in dry season. There were 5 medium-niche species(2.0>B_ij ≥ 1.0) in flood season and 8 species in dry season, whereas there were 10 narrow-niche species(1.0>B_ij> 0) in flood season and 4 species in dry season. The degree of Q_ij was different obviously in the two seasons. There were 41 pairs of species with significant Q_ij in flood season, accounting for 34.17% of the total number of pairs, with a relatively high overlap degree. Conversely, the major fish species overlap degree in dry season was low, with 19 pairs of species with significant overlap, accounting for only 24.36% of the total number of pairs. RDA showed that depth and total phosphorus(TP) were the factors directly affecting the distribution of the major fish species, which exhibited obvious niche differentiation.【Conclusion】 Obvious differences are found in spatial niche of different feeding fishes in Qingshitan Reservoir at different seasons and places. Whether in flood season or dry season, the B_ij of omnivorous fishes is large, that is, omnivorous fishes occupy a wider ecological niche than other predatory fishes do, and omnivorous fishes have a strong competition relationship with herbivorous fishes.