The hairtails centtal fishing ground of Shengshan is situated at Lat. 30°00'-31°10'N, and Long. 122°30--123°40'E, under the proper water temprature of 17-22℃ in winter. The shift of the fishing ground seems to be closely related with the changeof the nearby front of a high salt water tongue. The hairtails central fishing ground islocated on the north side of the front. In ordinary years, the front of the tongue changesvery little at the beginning and at the middle of the fishing season, but it moves south-ward at the end of the season. The changes usually appear in three types. 1. During the fishing season, While the actions of the wind and the sea current arerelative balanced, the front of the tongue is stable, but it gradually retreats southward atthe end of the season. 2. During the fishing season, the turbulence of the gale disturbs the balance, itmakes the front to retrcat southward earlier than ordinary. 3. During the fishing season, the wind force is weak, and the sea current for thefishing-ground is obvious, so that the front retreats at first and advances then. The central fishing ground shifts coincident with the change of the above types andthe fish schools correspondingly appear stable, and moving near south or north. After all, the movement of the front of the tongue is regarded as the index ofhairtails contral fishing--ground shifting and the marine enviroments changes. Practicallysometimes the index appears in effectual, in caso of: (A) When the front is in thesouth of Lat. 30°N; (B) When the axis of the front is in the east of Long. 123°30'E. In such abnormal cases, other factors should be considered.