To understand the correlation between the hypoxia tolerance ability and the hemoglobin (Hb) in fish. A total of 12 different species of fish, Catfish (Silurus meridionalis), Snakehead (Channa argus), California Perch (Micropterus salmoides), Channel Catfish (Ictalurus punetaus), Yellow Catfish (Pelteobagrus fulvidraco), Loach (Misgurnus anguillicaudatus), Eel (Monopterus albus), Grass Carp (Ctenopharyngodon idellus), Erythroculter Ilishaeformis (Erythroculter ilishaeformis), Silver Carp (Hypophthalmichthys molitrix), Big Head Carp (Aristichthys nobilis) and Chinese Perch (Siniperca chuatsi), were collected from Luhu Fishery and suburban of Wuhan. The hemoglobin was extracted from blood of each species separately. By using vertical polyacrylamide gel electrophoresis technology, the hemoglobin of each species was analyzed. Compared to logarithm of the standard protein molecular weight and mobility of standard curve, the mobility and standard curve of hemoglobin molecular weight was obtained after electrophoresis. With gel image analysis software Bandscan V5.0, the relative content of each hemoglobin band was measured, and the average hemoglobin molecular weight was calculated for each fish. The suffocation points of 12 species fish were determined by closed hydrostatic device. The results showed that the hemoglobin electrophoretograms were not identical (Fig. 1). Their hemoglobin molecular weights were: 92.93, 93.91, 94.61, 97.78, 98.66, 98.95, 101.34, 104.10, 104.73, 108.06, 108.23, 111.84 (ku), respectively, and their asphyxiation points were 0.15, 0.18, 0.30, 0.27, 0.36, 0.26, 0.24, 0.39, 0.42, 0.51, 0.46 and 0.59 (mg/L), respectively (Table 3). The correlation analysis found that asphyxiation point and the hemoglobin molecular weight were significantly positive correlated (r = 0.925, P < 0.01).