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vol-3SOME BIOLOGICAL CHARACTERS OF
MUGIL CAPITO (CUV.) IN LAKE BOROLLUS
BY
EL-MAGHRABY. A. M., M. T. HASHEM A~D H. M. EL-SEDFY
ABSTRACT
nULLE’I’IN OF THE INSTIT”UTD OF OCEANOGHAPRY & FISHERIES 57
The length distribution of M. capi(a in lake Borollus wasfollowed
throughout the year according to age and sex, especially in the
spawning season, and the length-weight relationship for the different sexes was made. It was found that the spawning period
affects the weight and consequently the condition factor of the
fish, they have low values for the spent fish (late winter and early
spring), and high values during late spring and summer.
The formula of length-weight relationship was estimated for
sepcrate soxes and for both sexes combined;
For males : log W = -4.5647 + 2.7612 log L
For females :log W = -4.9029 + 2.9392 log L
For both sexes: log W = -4.4244 + 2.8071 log L
Tho exponent (n) was high for the ripe females in the period from
October to December and the formula was as follows:
log W = -5.2224 + 3.0464 log L
It was found that a fry ring was present in most of the scales
examined for fisheslonger than 70 mm in length. The winter ring
is usually formed during April. The discrepancy in the calculated
lengths of different age groups are not very large, and the maximum
annual increase in legnth takes place during the first year of life.
The calculated weights for females are higher than for males, and
the maximum addition in weight is achieved in the third year of life.
Net sclectivity is the main factor that can affect the length distribution of ll1. capite in Lake Borollus. The population is
dominated by fishes of age group I as a result of intensive fishing
with nets 0 f illegal mesh sizes. This also affected the life span of the
fish in the lake rendering it short, no t exceeding four years of life.
Thc length frequency of M. capita in the oatch of Lake Borollus
ranges between 100 and 340 mm, with a distinot peak at lengths
140-240 mm., whioh represent fishes of age group I. As regards
the sex ratio, the percentage of female exceeds that of males for
all collections except in two months (February and November).
For the whole period of investigation an average ratio of 1.6
females to one male was recognised
