Walleye pollock Theragra
chalcogramma during transformation from the larval to juvenile stage:
otolith and osteological development
A.L. Brown, M.S. Busby, K.L. Mier-2001
Marine Biology, 139(5): 845-851
Abstract:
Walleye pollock [Theragra chalcogramma
(Pallas, 1814)] were collected from the Gulf of Alaska from 1991 to 1998 to
examine the relationship between otolith and osteological development during
transformation from the larval to juvenile life stage. Five stages of
otolith development were determined for walleye pollock in conjunction with
landmarks in osteological development during juvenile transformation. The
first stage of otolith development (12-19 mm SL) is identified by the
first accessory growth center (AGC) forming on sagittal otoliths. At this
stage, the notochord is undergoing flexion as the teeth, jaws,
branchiostegal rays, neural spines, and abdominal vertebral centra are
ossifying. The second and third stages of otolith development (19-21 and
21-24 mm SL) are defined by the formation of the anterior, posterior,
and dorsal AGCs on the otolith. This occurs during postflexion in
conjunction with ossification of the principal caudal-fin rays, haemal
spines, and caudal vertebral centra. The fourth stage of otolith development
(24-37 mm SL) is defined by the AGCs on the ventral edge of the
otolith. By this stage of development, the pelvic-, pectoral-, dorsal-, and
anal-fin ray elements have started ossification and the fish has entered the
transformation stage. The fifth stage of otolith development (36-48 mm
SL) is identified by a completely formed sagittal otolith, which has AGCs
that have grown together so that the otolith shape resembles an adult
otolith, the ossification of all vertebrae and fin rays is complete, and the
fish is a juvenile. By estimating what length a fish was, based solely on
otolith development, would prove helpful for those who wish to reconstruct
length frequencies of walleye pollock from otoliths of fish that have been
damaged due to gear and/or poor handling during the preservation process.