Burchard et al Maturity indices and field sampling practices for staging Melanogrammus oeg/efinus 
101 
Table 5 continued 
Hydration stage 1 (HI) 
Macroscopic: The ovary is well developed, reddish-yellow in color, and approximately 2/3 
the volume of the body cavity. The membrane is opaque and has prominent blood vessels. 
The contents consist mostly of yellow-looking oocytes and <25% of the ovary contains 
large translucent (hydrated) oocytes. 
*Note: In the early phase of the HI stage, the ovary is not visually homogeneous and 
hydrated oocytes can be unevenly scattered throughout. If microscopic analysis will be 
conducted on a subsample, take care to obtain a representative tissue sample that in- 
cludes translucent, hydrated oocytes. Document with a photograph of the whole ovary if 
possible. 
Microscopic: There is a predominance of tertiary vitellogenic oocytes, with many oocytes 
showing oocyte maturation, germinal vesicle migration and germinal vesicle breakdown. 
A small percentage of oocytes (<25%) will have completed oocyte maturation and are hy- 
drated. Postovulatory follicles may be present (magnification 100x). 
Hydration stage 2 (H2) 
Macroscopic: The ovary is well developed, reddish-yellow in color, and approximately 2/3 
the volume of the body cavity. The membrane is opaque with blood vessels conspicuous. 
The visible surface of the ovary consists of 25-50% of large translucent oocytes. 
*Note: There are gradients between the consecutive HI and H2 stages as well as the H2 
and H3 stages, where it is difficult to assign one or the other stage. In these cases, the 
ovary is at a state where it is either close to entering the H2 stage or close to advanc- 
ing to H3. In both cases the ovary is near if not in an intermediate phase of final oocyte 
maturation and may be accurately classified as H2. 
Microscopic: There is a predominance of oocytes showing germinal vesicle migration and 
germinal vesicle breakdown. Approximately 50% of the advanced oocytes are hydrated. 
Postovulatory follicles may be present (magnification 40x). 
Regenerating stage 
The histological results for RE stage ovaries reflected 
the difficulty in distinguishing between a regenerating 
and regressing ovary in the field, with 46% of the ova- 
ries classified as RE in the field assigned as S during 
histological analysis. The plausible explanation for this 
result is observational error. As the ovary progressed 
into the RE stage, it became easier to differentiate 
from the S stage, but, because of the short sampling 
period, it was difficult to differentiate between the 2 
stages during the time when regenerating fish were 
captured. For future studies, we recommend that sam- 
pling be conducted from well before to well after the 
known spawning season and that a photograph of each 
ovary be taken for comparison with histology-based 
staging results. Such documentation of the changes 
observed in different phases, from spent to regressing, 
could improve the ability to distinguish between these 
2 stages. However, extension of the sampling period too 
far into the fall and winter may make it more difficult 
to distinguish the D and RE stages from spawning stag- 
es (Tomkiewicz et al., 2003). Histological examination of 
a sample of an ovary was an effective way to determine 
if an ovary was in the RE stage. 
If a regenerating ovary was observed from a fish 
near or larger in size than the mean length at maturity 
during the peak spawning period, it is possible that 
