| dc.description.abstract | The reproductive biology, growth parameters, mortalities and exploitation rate of
Leptoscarus vaigiensis were investigated in a shallow inshore lagoon in the south coast of
Kenya. The overall male to female sex ratio was 1:1.4. Statistical analysis by Chi-square
showed that there is no significant different from the 1:1 ratio (P> 0.05). The monthly
male to female sex ratio did not show any consistent trend that could have been related to
the reproductive cycle.
Oocyte- size-frequency distribution coupled with histological analysis of the ovary
indicated unimodal distribution of oocytes in stages 1,2,3 and 6. A bimodal distribution
of oocytes is evident in ovaries at maturity stages 4 and 5. The bimodal distribution
included one mode of mature oocytes and the other mode made of immature oocytes.
These modes were not completely separated from the immature stock, and some
intermediate oocytes were evident between. the two modes. However, these oocytes
contained cytoplasmic vacuoles meaning that such oocyte will mature and will be
spawned together with the large sized ones. There is no progression of the mature oocytes
in ovaries in stage 6 of sexual maturity. At this stage, the ovaries contained only
immature stock of oocytes, with few degenerating oocytes. It was be inferred that an
individual fish probably spawns only once during the year ofstudy. However, the GSI
and Kn calculated for the fish population, showed that th~r.e were two peak spawning
times during the year of study, one between March and June"with a peak in April, and the
other between November and December. These months fall within the two intermonsoon
periods that are experienced in the East African region. There is therefore a possibility
that there are two breeding populations of L. vaigiensis at the area of study with each
having peak spawning at a specific intermonsoon period.
In the present study, the potential fecundity of L. vaigiensis ranged between 186,000 to
1,806,000 eggs. A mean potential fecundity of 674,000 eggs per female was determined.
Fecundity was significantly related to body weight and body length. The fish became
sexually mature at 16.8 cm, total length.
The length-weight relationships calculated for males and females were not significantly
different (ANeOV A: F = 14.9; P = 0.68) and a single regression was calculated which
adequately described the length-weight relationship of this species. The relationship
obtained was Logn, W = 2.86 LoglO L - 1.595. Growth and mortalities were determined
from length frequency data. The growth constants were estimated as K = 1.5 per year,
Loc = 28.9 cm and <1>1 = 3.10. Natural mortality was estimated from Pauly's empirical
formula (Pauly 1980) which was found to. be 2.30. Total (Z) and fishing mortality (F)
were estimated as 3.52 and 1.15 respectively. The estimated exploitation rate (F/Z)
estimated to be 0.33 is below the optimum exploitation rate of 0.5. This could be an
indication that the stock is not optimally exploited, though growth overfishing was
deduced to be taking place since the recruitment into the fishery occurs when the fish is
only 11.7 ern (total length) and the fish seems to mature at 16.] cm (total length). | en |
