Elevation of acid protease activity in the mantle muscle of female Japanese common squid todarodes pacificus during maturation

Abstract

Changes in the mantle muscle acid protease activity and the thickness of the mantle with sexual maturation were investigated in female Japanese common squid Todarodes pacificus from the Sea of Japan. The thickness index of the mantle was significantly lower in mature squid than in immature squid, and it decreased with an increase in gonadosomatic index, indicating that the mantle became thinner with maturation. The mantle muscle acid protease activity was significantly higher in mature squid than in immature squid, and it increased with a thinning of the mantle. In contrast to the acid protease activity, the mantle muscle protein content showed a tendency to decrease with a thinning of the mantle. These results suggest that the thinning of female squid mantle during sexual maturation is ascribed to the enhanced protein breakdown in the mantle muscle.