| dc.description.abstract | The reproductive biology of the Thumbprint Emperor, Lethrinus
harak (Forsskal 1775) was studied between April 95 - March 96
off the Kenya coast. The emphasis of the research was to compare
its fecundity estimates Using volumetric and stereologica1
methods.
Sampling was done twice a month during spring tides at Gazi
and Msambweni areas south of Mombasa. Beach seine nets of
variable mesh sizes (bag 28mm Wings 60mm) were used to catch
fish.
A total of 827 fishes was collected of which 386 were males, 426
were females and sex of the remaining 15 was not identified. The
fish caught were measured for total length, standard length and
weighed for their total body weight. .They were then dissected and
each gonad assigned to a maturity stage by visual inspection. For
females, these maturity stages were later validated by histological
examination of the internal organization of the ovary and by
taking oocyte diameter measurements.
The relationship between total length and total body weight for
males, females and the unidentified fishes was determined
separately. As the student's t-tests showed no significant
differences in the regression coefficients b of these groups, the
groups were thus pooled and a common regression line, Log10 W
= 2.97 Log10 L - 1.79 determined.
The overall sex ratio did not depart from the expected ratio of one
male to one female. But when data were stratified by size, chisquare
tests showed that males were predominant in the smaller
size classes while females predominated in the larger size
classes.
Length at which 50% of males and females attain sexual maturity
was found to be 24.5 cm and 26.1 cm total length respectively.
L. harak populations at the Kenya coast has a prolonged spawning
season extending from October to April with possibly two peaks
during October and again in February based on the cyclical
changes in the gonadosornatic index and the relative condition
factor; and the occurrence of high percentages of running and
spent fishes in the catches during these months.
Intra ovarian oocyte diameter frequency showed that L. harak has
a group synchronous oocyte development where there IS a
unimodal distribution in stage 1, 2, 3 and 6 ovaries and bimodal
one in stage 4 and 5 ovaries. In the later case, there is no distinct
size separation between the resting and the developing oocytes
suggesting that these oocytes are released In batches over a long
period.
Comparative fecundity estimates made using volumetric and
stereo logical methods showed that volumetric estimates were 23%
lower than stereolgical ones. A mean fecundity of 476,000
oocytes per female was determined. High positive correlation was
found to exist between fecundity and ovary weight. | en |
