International Journal of Marine Science2016, Vol.6, No.31, 1-7
4
Water quality parameters
The average water temperature during the four months of the study was 26
0
C while dissolved oxygen was 8mg
per liter (average). Data for pH was collected once per day and was fluctuated between the ranges of 6.5 – 8.6.
Figure 1 Egg spawning per class of wild and improved strain of
Oreochromis shiranus
Discussion
Growth of wild and improved strains of
Oreochromis shiranus
The observations show that all the three variables had influence on the number of eggs spawned. However, out of
the three variables; standard length has greater impact on number of eggs spawned than weight and total length
especially, for improved strain of
Oreochromis shiranus.
Standard length was significantly different at P= 0.001
(Table 4). Results of the present study corroborate those by Maluwa (1990) who reported that standard length had
greater impact in determining the number of eggs spawned by wild strain of
Oreochromis shiranus
. Standard
length has a greater influence on number of eggs spawned than the other variables because it represents the actual
body length which also determines the size of the visceral space in which the eggs are contained. The larger the
body size, the greater the space for egg development (El Sayed
et al
., 2003). On the other hand, body weight has
positive correlation with body length but do not reflect the actual size of the visceral space because a fish may
have heavy weight while its body length is shorter, thus providing a small visceral space for egg development.
Similarly, total length, which has an inclusion of the caudal fin to the standard length and do not provide any extra
fresh to contain the eggs. Findings of the present study agree with the reports by Sztramko and Teleki (1977); Tsai
and Gibson (1971); Bagenal (1978) that larger fish with a greater visceral space for egg development have larger
ovaries, and thus more eggs than smaller fish
.
The egg spawning trend between treatments changed with increase
in body weight and length but decreased as the fish continued to advance in weight and length (Table 1 & 3). The
results of the present study agree with the findings of Maluwa (1990) which show that number of ripe eggs in the
gonad increased with body weight and length. Peters (1963), Siddiqui (1977); Babiker and Ibrahim (1978) had
similar observations that there is an increase in egg number in the gonad with increasing body weight and length.
The quantity of eggs in the gonad is a reflection of the eggs brooded in the mouth despite that some are
reabsorbed. In addition, results of the current study have shown that there is a diminishing increase in number of
eggs from brooders above a mean body weight of 72g (14cm).
The results show that
Oreochromis shiranus
compared with other
Oreochromis
species deposit more eggs per
spawning interval, which ranges from 256 – 523 eggs from brooders weighing 41g to 133g (12cm -17cm) while
Oreochromis niloticus
, almost of the same length (12cm – 30cm) deposit 100 to 1,700 eggs (El-Sayed
et al
., 2003).
In another related study, Chimits (1957) reported that
Oreochromis mossambicus
brooders of 75g – 500g spawned
