OOCYTE DIAMETER EVOLUTION
ALONG THE YEAR AND BATCH FECUNDITY CM2000/Z:11
OF HAKE IN THE BAY OF BISCAY (ICES Div. VIIIa,b,d).
Hilario Murua, Marina Santurtún, Iñaki Quincoces & Paulino Lucio
AZTI Fundazioa. Txatxarramendi Irla s/n. 48395 Sukarrieta (Bizkaia). España. Tel: +34 94 687 07 00 Fax: +34 94 687 00 06
e-mail: hmurua@azti.es; msanturtun@azti.es; iquincoces@azti.es; plucio@azti.es
10˚
8º
6º
2˚ E
0˚
2˚W
4º
4º
49º
VIIj
6
24
65
17
VIIId 1
58
66
21
70
8
4
1
22
20
VIIIb
17
21
18
21
VIIIc
20
200 m
16
PASAJES
ONDARROA
43º
IXa
14
E3
E1
E5
E7
E9
F1
Batch fecundity vs Length
Only gonads with hydrated oocytes were used for fecundity studies. The samples were
collected between December-July of the period 1996-1997 and during March-April
1998. At the end of the study, a total number of 207 females (40-97 cm total length)
with hydrated oocytes were studied and more than 161,000 hydrated oocytes were
counted.
Batch fecundity
Intercept
-395847.0
37293.0
-10.6145
0.0000
Slope
9924.48
594.467
16.6948
0.0000
---------------------------------------------------------------------------------Correlation Coefficient = 0.76065
R-squared = 57.8589 percent
Standard Error of Est. = 76701.4
4
3
1
0
30
50
60
Length (cm)
70
80
90
200
At a 95 % confidence level, length ranges have a significant effect (p=0.0000) in batch
fecundity, but no interactions between this factor and the different months were
detected (Figure 3). Thus, a further analysis was carried out to detect which length
range contribute more in the batch fecundity differences. At a 95% confidence level,
batch fecundity calculated for each length range differ significantly between all groups
(p=0.000).
3
0,25
0,50
0,75
1,00
1,25
OOCYTES DIAMETER (mm)
1,50
9
6
3
0
0,00
1,75
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
AUGUST
FEBRUARY
50
500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000
NUMBER (mean)
15
0
12
9
6
3
0
0,00
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
15
12
9
6
3
0
0,00
2,00
0,50
1,00
1,50
2,00
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
Relative batch fecundity of mature female Hake
MARCH
200
NUMBER (mean)
250
SEPTEMBER
15
(b)
NUMBER (mean)
12
9
6
3
0
0,00
150
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
15
12
2,00
9
6
3
0
0,00
100
OCTOBER
APRIL
15
15
50
1.000
1.500
2.000
2.500
3.000
3.500
Means and 95.0 Percent Confidence Intervals
(X 100000)
4
1 = 40-49
2 = 50-59
3 = 60-69
12
9
6
3
0
0,00
Figure 2: (a) Batch fecundity by gram of female and (b)
relative batch fecundity calculated for Hake in Div.
VIIIa,b,d during the period [1996-1998]
NUMBER (mean)
Relative batch fecundity
300
Batch fecundity
To detect for differences in batch fecundity between different discrete fish sizes
and sampling months, a further analysis was carried out. Four length ranges were
chosen: 40-49, 50-59, 60-69 and > 70 cm. To balance the analysis, all those months, in
which not all length ranges were presented, were removed from the analysis. Thus, from
the synthetic period [December to July], January, June and July were eliminated.
6
12
100
Batch fecundity = -395820 + 9924.04 Length, (n = 205, r = 57.6513)
•
9
0
0,00
2
Batch fecundity appears to be rather constant in relation to the female weight
(Figure 2a, 2b). This is, by gram of female the same number of oocytes are produced
independently on their total or gutted body weight.
12
150
Gutted weight (g)
•
15
NUMBER (mean)
(a)
250
0
1. Batch fecundity
Batch fecundity appears to be dependent of fish total length (in cm) (Figure 1). A
significant relationship (p=0.0000) was found between both parameters. A linear
regression was adjusted and the equation obtained was:
JULY
15
0
500
•
>
This study supports the theory that large (older) Hake females in the Bay of Biscay
mature earlier and at mainly at the beginning of the first semester, while that smaller
(younger) females mature later and mainly at the end of the spawning season.
JANUARY
A preliminary study was deployed to check for statistical differences in the number of
oocytes between each lobule and between different parts of the gonad, but no
statistical differences at 95 % confidence interval were found. Whenever possible, 3 or
2 sub-samples were taken from the medium part of each gonad in the months of the
peak spawning period or in the rest of the year, respectively.
RESULTS & DISCUSSION
For bigger females (> 50 cm length), the largest and more frequent oocytes were
measured during the first half of the year, which coincide with the Hake spawning
period that is considered, by other studies, to be from January to May. During the
second semester these females presented only small and medium sized oocytes with a
total absence of largest oocytes.
Batch fecundity by grams of mature female Hake
Total weight (g)
At the end of the study 39 samples from females 40-50 cm length and 41 samples from
females >50 cm were studied and more than 14,400 oocytes were measured under a
profile projector provided of a digital measuring system. For each sub-sample the
diameters of 200 oocytes were measured and recorded. Mean frequencies of diameters
of 0.1 mm of interval were analysed along the whole year.
For smaller females (40-50 cm length), large amount of small oocytes appear during
January and start increasing their sizes along the first half of the year. In May, the
largest oocytes and a marked lack of oocytes between large and small sized ones are
found. In the second part of the year, larger amount of small size oocytes appear.
(There were not data for June and September, but from the Figure 4 monthly
sequence, the oocyte diameter for these two months was expected to follow the same
general pattern of contiguous months: higher frequencies of small oocytes and lower
numbers of medium-sized oocytes in June, and medium frequencies of medium and small
sized oocytes in September). The unexpected large frequencies of large size oocytes
of small females found in October are likely to be due to an inadequate number of
gonad sampled during this month.
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
12
9
6
3
0
0,00
2,00
12
9
6
3
0
0,00
3
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
NOVEMBER
MAY
15
NUMBER (mean)
A monthly study of the changing diameter of the Hake oocytes along a "synthetic"
biological year [1996-1998] was carried out. When possible, 5 females > 40 cm in total
length for each month of the "synthetic" biological year in the [1996-1997] period, and
all females > 45 cm length for the period March-April 1998 were chosen.
40
Figure 1: Adjusted regression to the batch fecundity data
calculated for different total length sizes of Hake in Div.
VIIIa,b,d in the period [1996-1998].
Batch fecundity by gram of mature
female
(Total weight)
Oocyte diameter evolution study
•
•
2
300
Values of "batch fecundity" (total number of hydrated oocytes), "batch fecundity by
gram of mature female" (total number of hydrated oocytes/female total weight), and
"relative batch fecundity" (total number of hydrated oocytes/female gutted weight)
were calculated.
Figure 4 shows the monthly distribution of the mean diameters of all the oocytes
measured, grouped in intervals of 0.1 mm, for smaller and bigger fish.
NUMBER (mean)
To check for possible statistical differences in the number of hydrated oocytes
between each gonad lobule and between different parts of the gonad, a previous study
was carried out. As no statistical differences at 95 % confidence interval were found
between them, random samples from the medium part of the right lobule of the gonad
were routinely used.
Three samples of rather similar weight (range 0.05-0.25 g) and from the medium part
of the gonad were taken. The epithelium covering the oocytes was meticulously removed
with a surgical blade and oocytes were carefully separated one from each other using a
lancet. Then oocytes were placed on a Petri plate and observed under a profile
projector provided of a digital measuring system. Hydrated oocytes (close to 1 mm or
bigger) of each sample were counted and recorded.
---------------------------------------------------------------------------------Parameter
Estimate
S.Error
T.Statistic
P-Value
----------------------------------------------------------------------------------
5
2. Evolution of the oocyte diameter along the year
F3
Map I: Allocation of the number of hauls deployed in the
period [1996-1998] to collect Hake gonads samples in Div.
VIIIa,b,d.
(X 100000)
6
>
Batch fecundity appears to be significantly determined by Hake size, but fish catch
month appears not to have a significant effect. These conclusions support the theory
than smaller and probably younger fish are able to produce less hydrated eggs than the
larger ones, and thus their batch fecundity is comparatively lower than the larger ones
and that the month effect does not appear evident in the batch fecundity values.
2,00
15
12
9
6
3
0
0,00
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
2
--------------------------------------------------------------------------------------------------Source
Sum of Squares Df Mean Square F-Ratio P-Value
--------------------------------------------------------------------------------------------------MAIN EFFECTS
A:Date
3.10391E10
4
7.75978E9
1.32
0.2658
B:Length range 5.61088E11
3
1.87029E11
31.79
0.0000
INTERACTIONS
AB
2.95136E10
12
2.45947E9
0.42
0.9545
RESIDUAL
8.29418E11 141
5.8824E9
--------------------------------------------------------------------------------------------------TOTAL (CORRECTED)
1.95413E12 160
---------------------------------------------------------------------------------------------------
1
0
1
2
3
4
Length range
Figure 3: ANOVA carried out to establish the effect of
fish length range in the batch fecundity of Hake in Div.
VIIIa,b,d. Means and 95% confidence limits of batch
fecundity in relation to length range are included. Size
ranges selected: (1): 40-49, (2) 50-59, (3) 60-69 and (4)
> 70 cm fish total length.
DECEMBER
JUNE
NUMBER (mean)
Fecundity studies
36
141 102
45˚
D9
Hake gonads were obtained at sea from commercial catches of longliners and trawlers
working in the Bay of Biscay (ICES Div. VIIIa,b,d) and with basis on the two main
Basque Country's fishing ports, Ondarroa and Pasajes, along the period 1996-1998 (Map
I). Gonads were fixed in 4% formaldehyde buffered solution, right after the fish was
caught, and later analysed at the laboratory.
67
42
47º
24
Number of hauls
allocated (869 ) by
ICES statistical
rectangle in
Div. VIIIa,b,d
for reproductive
studies of Hake
NUMBER (mean)
MATERIALS AND METHODS
60
NUMBER (mean)
Merluccius merluccius
VIIIa
26
1
NUMBER (mean)
Bay of Biscay (ICES Div. VIIIa,b,d) is considered one of the main spawning areas of the
so called northern stock of Atlantic European Hake (
). Due to the
economical importance and the stage of this stock, several studies on the reproductive
behaviour of this species have been conducted in the last years, some of them partially
founded by the E.U. DG XIV (Study Contract nº 95/038 (BIOSDEF) and nº 97/015
(DEMASSESS)).
VIIe
VIIh
NUMBER (mean)
INTRODUCTION
15
12
9
6
3
0
0,00
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
15
12
9
6
3
0
0,00
0,50
1,00
1,50
OOCYTES DIAMETER (mm)
2,00
Figure 4: Bay of Biscay Hake oocyte diameter evolution along a synthetic year in the
period [1996-1998]. Red dots correspond to < 50 cm length fish and blue dots to > 50 cm
length fish.
ACKNOWLEGMENTS
This study was founded by the European Union DG XIV (Study Contract nº 95/038 (BIOSDEF) and nº 97/015 (DEMASSESS)) and by the Department of Agriculture and Fisheries of the Basque Country Government.