When I found this little specimen (18-20 mm), it was in this position, inside the spiral sausage-shaped structure...

After about 10 minute, It leave the spawn...

You can see the spiral sausage-shaped structure of the spawn.

According to Willan (1984) it lays a flaccid white spawn coil. Ova measuring 75-95 µm occur singly in capsules (up to 190 µm diameter) that are loosely coiled in cylinders within the spawn. Approximately 315 ova make up a single spawn.

In this spawn, there are obviously more than 315 ova...