Osservazioni sulla biologia e la pesca dello storione cobice Acipenser naccarii Bonaparte nella parte terminale del fiume Po

In the Po River area three species of sturgeons have been recorded during the seventies; of these, the sturgeon (Acipenser sfurio), and the beluga (Huso huso), up to now have practically disappeared from the river. Only the endemic Adriatic sturgeon, Acipenser naccarii, is still present and captured by fìshermen, but its abundance is relatively low. The Adriatic sturgeon grows less than its congenerics, attaining the maximum length of 161 ± 14 cm. Nonetheless, during first years of life it grows very quickly: at the end of second year it is about 50 cm long and weights about 1 Kg. Later on, it needs about 10 years to achieve the size of 1 m and thè weight of 8-9 Kg. Sexual maturation of males starts when they are longer than 80 cm, and 6 to 8 years old: on the contrary, mature females occur only when they overcome the length of 100 cm. Most of the examined Adriatic sturgeons are parasitized by acantocephalans: when heavy affected, their growth performances are also reduced. The abundance of the Adriatic sturgeon population was heavily compromised by fìshing: more than 80% out of about 2000 specimens sold at the fish market during the 1981-88 period weighted less than 3.5 Kg and were therefore fished before the reproductive phase. Besides fìshing, the reduction of thè Adriatic sturgeon population is also a consequence of Po River pollution and of the building of a dam along the river