The eggs of the Bass, Morone labrax (L.), in British waters, are larger than those of the Mediterranean eggs observed by Bertolini (1933).
These eggs hatch on the fourth day, and the mean length of newly hatched larvae is 3.83 mm. By the end of twenty-four hours this length has increased to 4.85 mm., by the third day to 4.98 mm., by the fourth day to 4.99 mm. and on the tenth day the mean length is 5.61 mm.
During the first twenty-four hours, the early post-larval stages rest for long periods at the surface of the water. On the third day the larvae begin to sink slowly when at rest, and normal horizontal swimming is commenced on the sixth day. By the tenth day the larvae swim with the mouth open.
From the observed rate of growth of these reared larval stages, it is likely that those taken in the plankton hauls off the Eddystone during the period 1925–1933 (Russell 1935) were from three to fifteen days old.