The sheatfìsh is an exotic species which before the eightieth was only sporadically found in the Italian waters: it is now, on the contrary, an important component of the fish fauna in the lower part of the Po river where it is fished and sold on the fish markets. The total quatity fished per year is increasing, starting from 1983, but the commercial value decreased progressively so as it is sometime captured and released. The sheatfish grows very rapidly in the Po river, showing a growth rate better than that observed in the original regions, probably because of a better thermic situation and the lack of competition and predation. The histological analysis of the gonads shows that the male attains thè sexual maturity at a total length of about 60 cm, while the female at a length of about 70 cm, when it is 3 years old. The spawning period lasts a long time, at least from May to September. Up to 30 cm of length the sheatfish diet consists mainly of crustaceans (especially gammarids) and insect larvae; but starting from 30 cm of length it becomes piscivorous and preys upon cyprinids. The examined sheatfish were parasitized by 4 species of acanthocephalans. As a conclusion the Authors discuss some management hypotheses to control the sheatfish abundance in the Po river.
Biologia ed ecologia di una specie alloctona, il siluro (Silurus glanis L.) (Osteichthyes, Siluridae) nella parte terminale del fiume Po
ROSSI, Remigio;RIZZO, Maria Grazia;FRANZOI, Piero;GRANDI, Gilberto
1991
Abstract
The sheatfìsh is an exotic species which before the eightieth was only sporadically found in the Italian waters: it is now, on the contrary, an important component of the fish fauna in the lower part of the Po river where it is fished and sold on the fish markets. The total quatity fished per year is increasing, starting from 1983, but the commercial value decreased progressively so as it is sometime captured and released. The sheatfish grows very rapidly in the Po river, showing a growth rate better than that observed in the original regions, probably because of a better thermic situation and the lack of competition and predation. The histological analysis of the gonads shows that the male attains thè sexual maturity at a total length of about 60 cm, while the female at a length of about 70 cm, when it is 3 years old. The spawning period lasts a long time, at least from May to September. Up to 30 cm of length the sheatfish diet consists mainly of crustaceans (especially gammarids) and insect larvae; but starting from 30 cm of length it becomes piscivorous and preys upon cyprinids. The examined sheatfish were parasitized by 4 species of acanthocephalans. As a conclusion the Authors discuss some management hypotheses to control the sheatfish abundance in the Po river.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
