International Journal of Marine Science2016, Vol.6, No.31, 1-7
2
wild or improved strain of
Oreochromis shiranus
is able to produce
.
In Malawi, most hatchery operators use
brooders with low spawning rate. This has been caused by inadequate data on the reproductive biology of
Oreochromis shiranus
. Previous studies on fish farming in Malawi placed much emphasis on nutritional,
technological and sociological aspects (Noble, 1990). Limited studies if any have been conducted on the effect of
biological and environmental factors on quantities of eggs spawned by
Oreochromis shiranus
species, which is
paramount in choosing fish brooders that can give adequate number of eggs.
The present study was aimed at establishing guidelines for
Oreochromis shiranus
brooders selection which can
give optimum number of eggs to meet the ever growing demand for fingerlings by both subsistence and
commercial fish farmers in Malawi.
Methodology
The experiment was conducted at the National Aquaculture Centre (NAC), Zomba, and southern Malawi from the
month of November to March. A total of 360 wild and improved brooders for
O
.
shiranus
were collected from the
same centre and categorized into three ranges from 24 – 59 cm (9 -14cm) for treatment 1, 60 – 99g (14 – 16cm)
for treatment 2 and 100 – 200g (16 – 20cm) for treatment 3. The brooders were stocked at a male: female ratio of
1: 3 in hapa nets placed in ponds (6×3×1m) in size at 5 fish per m
3
. Fish were fed twice a day with Malawi Gold
Standard (18% CP) feed at 3% daily body weight. Sampling was done every two weeks during which eggs were
collected from the mouth of brooders. Water quality parameters: temperature, Dissolved Oxygen (DO) and pH
were measured every day.
Data Analysis
Data was analyzed in SPSS (version 16.0) and One Way Analysis of Variance (ANOVA) was used to compare the
treatment means. The significantly different treatment means were separated using Duncan’s Multiple Range Test.
Results
Wild strain –
Oreochromis shiranus
The proportion of female weight to number of eggs spawned is shown in table 1. The number of eggs increased as
the body weight and length of fish increased. The mean minimum number of eggs spawned by 180 wild brooders
in all treatments was 256 eggs and the mean maximum number was 523 eggs. The smallest number of eggs was
141, spawned by a brooder weighing 36g (SL: 11.6cm) and the largest number of eggs was 785, spawned by a
brooder weighing 103g (SL: 16.3cm). There was a rapid increase in number of eggs for wild strain brooders
weighing between 41-72g. However, the number of eggs started to increase at a decreasing rate after the brooders
attained 72-134g.
Table 1 Mean number of eggs spawned by wild strain of
Oreochromis shiranus
Treatment
Body weight
SL
TL
Eggs
1
41.45±1.35
11.73±.15
14.292±.19
256.38±6.4
a
2
71.95±1.08
14.413±.09
17.557±.11
418.60±8.0
b
3
134.20±3.99
17.480±.18
21.062±.19
523.2±12.50
c
Means with different superscripts within a column are significantly different (P<0.05)
Relationship of body weight (BW), standard length (SL) and eggs of wild strain brooders
Number of eggs, body weight, total and standard length was significantly correlated with BW (r = 0.70; P<0.01;
n= 180, SL(r = 0.75; P<0.01; n = 180; and TL(r= 0.74; P<0.01; n = 180. The relationship between body weight
and eggs, standard length and eggs was curvilinear while the relationship between standard length and body
weight was linear.
Using the enter method to establish the correlation of the variables, the adjusted R square was 56% and other
results are indicated in table 2.
