Burchard et al.: Maturity indices and field sampling practices for staging Melanogrammus aeglefinus 
103 
Table 5 continued 
Macroscopic: The ovary is small and firm, and approximately 1/6 the volume of the body 
cavity. The membrane is thin but less transparent, yellowish-gray. Contents are micro- 
scopic, opaque. 
Microscopic: The ovary wall is thick. There is often indication of past spawning with rem- 
nants of unabsorbed material. The ovary contains primary oocytes that vary largely in 
diameter (magnification 100x). 
Regenerating (RE) 
*Note: If a resting ovary is observed from a fish greater in size than the mean length at 
maturity during the peak spawning period, then it is probable that the fish skipped that 
year’s spawning season. 
of POFs occurs for the Spotted Seatrout (Cynoscion 
nebulosus) in 24-36 h in water temperatures >2°C 
(Roumillat and Brouwer, 2004) and for the Northern 
Anchovy ( Engraulis mordax) in 48 h at 19°C (Hunter 
and Macewicz, 1985). The atrophy of Haddock POFs 
may take much longer because this species prefers to 
spawn in cold temperatures (4-7°C; Overholtz, 1987) — 
an actuality that may be widespread in boreal fishes. 
The slow degeneration of POFs in cold-water species is 
supported by Brown-Peterson et al. (2011) and noted 
by Saborido-Rey and Junquera (1998). 
Aging of POFs has been used in other species to de- 
termine spawning frequency or duration of time since 
the female last spawned a batch of eggs (Hunter and 
Macewicz, 1985; Roumillat and Brouwer, 2004). No de- 
finitive information on diurnal timing of spawning was 
clear from our inspection of Haddock POFs because 
none of them appeared to have been very recently cre- 
ated. Fish collections were concentrated in an area 
where active spawning took place, and those Had- 
dock that had finished spawning may not have been 
available for capture. Observation of many ovaries in 
spawning condition that also showed many phases of 
POF atrophy indicated that these residual tissues had 
a very slow rate of atrophy and were of little use in 
making accurate assessments of diel timing of ovula- 
tion. A more advanced study of aging POFs in cold-wa- 
ter species similar to the studies done for clupeiforms 
by Alday et al. (2010) and Haslob et al. (2012) is need- 
ed and would increase our knowledge on the timing of 
spawning in cold waters. 
There were no equivalent field index stages for the 
histological stages 4.1 and 4.2. Samples classified as 
4.1 or 4.2 were typically assigned to an ovary in a state 
between the last batch of oocytes spawned and the next 
batch to be spawned, a state that we did not attempt 
to identify in the field. In ovaries of this state, no oo- 
cytes for the next batch had yet progressed to OM and 
the only oocytes present were in a vitellogenic devel- 
oped phase equivalent to the resting stage described by 
Murua et al. (2003). We found that this stage was not 
easily or accurately ascertainable through macroscopic 
observation of the ovary. A trained eye may be able to 
recognize a degree of flaccidity of an ovary that has 
spawned already. Many of the ovaries assigned as 4.1 
or 4.2 exhibited characteristics of an ovary that was 
classified as the D stage in the field. The overestima- 
tion of the D stage in this study indicates the need to 
conduct histology on a subsample of ovaries classified 
as D stage in the field to assure there is no indication, 
on the basis of the presence of POFs, that females thus 
classified have started spawning that season. 
Conclusions 
Working independently, we came to the same conclu- 
sion as Brown-Peterson et al. (2011): standardization of 
maturation staging methods and terminology are need- 
ed. Our study confirms the importance of these efforts 
but extends them with the development of a new ovar- 
ian maturity index specifically for examination of diel 
spawning periodicity while using the maturation ter- 
minology established by Brown-Peterson et al. (2011). 
Comparison of macroscopic and microscopic observa- 
tions of ovaries helped us to improve the initial field 
index and sampling methods, as well as to provide use- 
ful insight into the reproductive biology of Haddock. 
