West Coast Groundfish Observer Program Manual, Part2 - NOAA

CHAPTER 6
Sexing Sablefish
The gonads of sablefish are very different from all other
roundfish. They are located directly on the backbone,
forward toward the head of the fish. Cut up from the anus
to the collar to get a clear view. Alternatively, make a cut
down from the lateral line to the belly, just behind the
operculum, and then another insertion along the belly to
the mid-point. Remove all the other organs from the
visceral cavity and peer at the backbone area near the
posterior of the cavity to look for the gonad tubes. Both
females and males have fleshy smooth tubes which are
cream or pink in color. Mature fish have liver colored
gonad tubes while immature fish will have nearly seethrough
ribbons. There are no reliable differences in color
or texture to differentiate between non-ripe males and
females.
To differentiate between the sexes, probe the gonads lobes
apart and count the lobes. Males will have four lobes and
females will have two lobes. Be cautious when checking the
number of gonad lobes. When mature, the ovaries may
have a partial fold through each of the two lobes, giving a
false impression of four lobes. Cut across the gonad
strands to distinguish the true number of lobes.
Also be sure to look at the posterior part of the gonad.
The lobes of males are fused at the anterior point of the
gonad. Since the lobes will be fused anteriorly, they will
always look like two lobes at this location and can be
mistaken for female gonads.
1/30/2004 6-19