869 
The effects of formalin and freezing on 
ovaries of albacore, Thunnus alalunga 
Darlene Ramon 
Norm Bartoo 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
La Jolla, California 92038 
E-mail address (for D. Ramon): Darlene.Ramon@noaa.gov 
In almost every biological sampling 
program, tissue samples are col- 
lected and preserved for further 
examination. In this study, the ef- 
fects of freezing and 10% buffered 
formalin on albacore, Thunnus ala- 
lunga, ovaries are compared to ex- 
amine how each method of preser- 
vation affects ovarian weight and 
oocyte diameter. Formalin is fre- 
quently used to preserve ovaries for 
histological studies but, due to its 
toxicity, it may not be a good choice 
in all cases, and alternative meth- 
ods, such as freezing, should be in- 
vestigated. There is limited infor- 
mation on the effects of preserva- 
tion on tuna gonads and, specifi- 
cally, on albacore gonads. We inves- 
tigated the effects caused by freez- 
ing and 10% buffered formalin on 
weight and oocyte diameter, be- 
cause weight and other measure- 
ments (such as oocyte diameter) 
from fresh samples are not consid- 
ered interchangeable with those from 
preserved samples (Lagler, 1968). 
The purpose of our investigation 
was to compare fresh ovarian 
weights with weights of frozen ova- 
ries and formalin-preserved ovaries 
from albacore as well as to deter- 
mine how the diameters from oo- 
cytes are affected by differing meth- 
ods of preservation. 
Materials and methods 
Albacore are seasonal spawners, 
spawning mainly during summer 
months (Otsu and Uchida, 1959; 
Ramon and Bailey, 1996). Ovaries 
were collected from albacore caught 
from 1990 to 1993 (Table 1) with 
longline gear in the South Pacific 
(group A) and in waters off Hawaii 
(group B) and with trolling gear in 
the North Pacific (group C). In 
group B, samples were labeled as 
one of three subgroups (Bl, B2, or 
B3) on the basis of the method of 
preservation used (Table 1). 
In the South Pacific, ovaries from 
each collected fish were dissected 
and preserved; a total of 150 pairs 
were collected. In the North Pacific, 
sampling took place at two sites: 
1) between latitude 42°33'N and 
52°02'N and from longitude 129°00'W 
to 145°52'W and 2) in the waters off 
Hawaii. Table 1 lists the methods of 
preservation used for all samples. 
To investigate the effects that 
freezing and 10% buffered forma- 
lin have on oocyte diameter, we ex- 
amined oocyte diameters from 58 
immature North Pacific albacore 
from 70 cm to 89 cm fork length 
(FL) in group C. Right-side ovaries 
were preserved in 10% buffered for- 
malin; left-side ovaries were frozen 
until processed two months later. 
The diameters of the most devel- 
oped oocyte for each side of the 
ovary were measured to the near- 
est 0.01 mm and compared statis- 
tically with Student’s £-test. 
To compare differences in oocyte 
diameter and weight between the 
two methods of preservation, we 
used ovaries from subgroup B, 
which consisted of large, mature 
albacore (>95 cm FL). The mean 
diameter of oocytes in the most de- 
veloped mode was measured from 
each side of the ovary and com- 
pared statistically with Student’s t- 
test. The most developed mode of 
oocytes was determined with the 
criteria and method described by 
Schaefer (1987). 
The effect of preservation on ova- 
rian weight was examined for all 
samples collected in Hawaii (group 
B). Ovaries in group B were weighed 
fresh to the nearest 0.1 g and were 
then either preserved in 10% buff- 
ered formalin or were frozen. The 
samples were then reweighed two 
to three months later; samples pre- 
served in 10% buffered formalin 
were placed on a paper towel, and 
excess moisture was patted off be- 
fore they were weighed to the near- 
est 0. 1 g on a Mettler PM3000 elec- 
tronic balance. Frozen samples 
were thawed before being placed on 
a paper towel, and excess moisture 
was patted off before they were 
weighed. 
The preserved weights of ovaries 
were compared with fresh weights 
by means of Student’s t-test. 
Results and discussion 
Effect of preservation on 
oocyte diameter 
Because measurements of oocyte 
diameter were not made on fresh 
oocytes, we assumed that left and 
right ovaries develop at the same 
rate. This assumption was tested 
with preserved specimens. Mean 
oocyte diameters of oocytes in the 
most developed mode in the right 
and left ovaries in group A were 
compared with mean oocyte diam- 
eters of oocytes in subgroups B2 
and B3. The results indicated no 
Manuscript accepted 4 April 1997. 
Fishery Bulletin 95:869-872 (1997). 
