Stereological comparison of oocyte recruitment and batch fecundity estimates from paraffin and resin sections using spawning albacore (Thunnus alalunga) ovaries as a case study.
Traditional histological protocols in marine
fi
sh reproductive laboratories using paraf
fi
n as the embedding
medium are now increasingly being replaced with protocols using resin instead. These procedures entail differ-
ent degrees of tissue shrinkage complicating direct comparisons of measurement results across laboratories or
articles. In this work we selected ovaries of spawning Mediterranean albacore (
Thunnus alalunga
) as the subject
of our study to address the issue of structural changes, by contrasting values on oocyte recruitment and
fi
nal
batch fecundity given from the same tissue samples in both paraf
fi
nandresin.Amodernstereologicalmethod,
the oocyte packing density (OPD) theory, was used supported by initial studies on ovarian tissue sampling and
measurement design. Examples of differences in the volume fraction of oocyte stages, free space and connective
tissue were found between the embedding media. Mean oocyte diameters were smaller in paraf
fi
nthaninresin
with differences ranging between 0.5% in primary growth and 24.3% in hydration (HYD) stage oocytes. Fresh
oocyte measurements showed that oocytes shrank as a consequence of the embedding process, reaching the
maximaldegreeofshrinkageforoocytesintheHYDstage(45.8%inparaf
fi
nand26.5%inresin).Inordertoassess
the effect of oocyte shrinkage on the OPD result, and thereby on relative batch fecundity (F
r
), oocyte diameters
corrected and uncorrected for shrinkage, were used for estimations. Statistical signi
fi
cant differences were
found (
P
b
0.05) between these two approaches in both embedding media. The average F
r
was numerically
smaller in paraf
fi
n compared to resin (86 ± 61 vs. 106 ± 54 oocytes per gram of body mass (mean ± SD)).
For both embedding media statistical signi
fi
cant differences (
P
b
0.05) were seen between F
r
results based on
either oocytes in the germinal vesicle migration stage or HYD stage. As a valuable adjunct, the present use of
the OPD theory made it possible to document that the oocyte recruitment of spawning ovaries of Mediterranean
albacore followed the typical pattern of an asynchronous oocyte development and indeterminate fecundityPostprint2,444