الفهرس 
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Abstract
Members of family cichlidae are considered as an important food
source in Egypt forming about 46% of total inland catch (Anonymous
2001) and representing 63% of the total fish catch in EI-Nozha
Hydrodrome during the period from 1997-2001 (Anonymous, 1968-2001).
The present investigation deals with the biological and fishery studies
of the main cichlid species (Oreochromis aureus, Sarotherodon galilaeus
and Tilapia zillii) in EI-Nozha Hydrodrome during the period from January,
1998 to December 1999.
The analysis of data comprised biomet ric, growth studies, food and
feeding habits, reproduction and fishery analysis including the population
dynamics of these cich1id species.
For biometric study, analysis of twenty morphometric measurements
of the three cichlid species in El-Nozha Hydrodrome shows that nine
morphometric indices out of nineteen have no significant variations for 0.
aureus and S. galilaeus. These are S.L., H.L., Pr.P., Y.L., Pr.A., Pd.L,
Pd.D, Pr.O and E.D. indices. For 0. aureus and T zillii, only two indices
namely Pr.A. and B.D. have non-significant differences. In case of S.
galilaeus and T zillii only five indices (D.F.L., V.F.L., Pr.A, Pd.D and
E.D) show non significant variations. The comparison of meristic counts
(Pectoral fin rays, Dorsal fin spines, Dorsal fin rays, Anal fin rays,
Vertebral number and Caudal fin rays) between these species shows that
non significant variations are found between 0. aureus and S. galilaeus while non significant variations are found in pectoral fin rays and caudal
fin rays for 0. aureus & T zillii and S. galilaeus & T zillii.
Comparison of the different morphometric indices of the three cichlid
species in El-Nozha Hydrodrome with those given by other authors in
different regions showed significant differences in most morphometric
indices. These variations probably reflect variations in ecological
conditions in different regions.
The relationship between length & gutted and length & total weight
revealed that the exponent (b) in both sexes for 0. aureus & T zillii and
female S. galilaeus were found to be equal to the cube of length (isometric
growth) whereas in case of male S. galilaeus it deviated from the cube of
length showing allometric growth.
The comparison between condition factor of cichlid species in El-
Nozha Hydrodrome showed that T. zillii have higher value as compared
with those of S. galilaeus and 0. aureus. Seasonally, higher values of
condition factor in all species were observed during spring while the lowest
values were observed in autumn for 0. aureus and in winter for S. galilaeus
and T. zillii.
Scales of cichlid species were used for age determination and growth
studies. It was observed that only one annulus was formed yearly in May
for S. galilaeus and T. zillii whereas it was recorded in June for 0. aureus.
The annual growth in length for the three species were observed to be large
in the first year of life and decreased as the fish grows older. Generally the
growth in length in case of S. galilaeus was higher than that of 0. aureus
and the latter was higher than those reported for T zillii. Growth rate in
weight of the same age group was found to be large in case of S. galilaeus than that of 0. aureus and T zillii. For all species the annual weight
increments tend to increase with increasing age. The application of von
Bertalanffv growth equation shows that the theoretical maximum length
for males and females 0. aureus were 34.3 em and 32.9 ern corresponding
to 12 years and 11.3 years respectively. For S. galilaeus it was found to be
33.1 em and 10.0 years for males and 35.2 ern and 12.0 years for females.
For T zillii, the theoretical maximum length and age were found to be 27.5
ern and 11.1 years for males and 22.3 em and 7.2 years for females.
The studying of food and feeding habits in cichlid fishes showed that
T zillii have higher value of fullness index in spring as compared with
those in other species (s. galilaeus and 0. aureus). For feeding diversity
(H’) the results obtained show that 0. aureus and S. galilaeus have wide
food spectrum as compared with T zillii. Analysis of food contents,
revealed that the main food items taken by 0. aureus were of animal origin
of which protozoan prey were the most dominant food. For S. galilaeus,
plant materials specially diatoms were found to be the main food items in
stomachs of this species. On other hands, plant detritus such as roots, stem
and grass blades were considerd to be the major food components in
stomachs of T zillii. Changing of food composition with regard to
changing fish size did not show any significant variation in all cichlid
species.
Regarding to seasonal variations of food, it was observed that food of
animal materials in case of 0. aureus were largely consumed in winter
while in both S. galilaeus and T zillii food of plant origins such as diatoms
and plant detritus were largely consumed in spring due to the marked
blooming of phytoplankton in the Hydrodrome. Generally, the three understudied cichlid species are considered to be
omnivorous i.e. eating food of both animal and plant materials.
Analysis of sex ratio (males/females) showed that males dominated the
catch in nearly all size groups for 0. aureus, S. galilaeus and T zillii with
exception of larger ones (26.0-30.0 ern) for the first species as females were
dominant. Also it was noted that males of the three species were abundant in all
seasons except in spring for 0. aureus where females were dominant.
The length at first sexual maturity for 0. aureus was 16.2cm and 15.0
cm for males and females respectively and 16.7cm, 16.2cm for males and
females S. galilaeus. Referring these lengths to their corresponding ages, it
was found that fishes of these two species mature after their second year of
life. For Tilapia zillii all examined fishes were sexually mature and they
were above 12.0 cm. This reveals that both sexes attain their first sexual
maturity at lengths less than 12.0 em at ages less than two years old.
Analysis of monthly distribution of maturity stages for the three
species revealed that the spawning season extends from April to August
with a peak during May for 0. aureus and T zillii and a peak in April for S.
galilaeus. It was found that both S. galilaeus and 0. aureus have markedly
large egg size (2.8-5.1 mm) and (2.3-4.8 mm) respectively than that of T
zillii (1.2-2.8 mm). So the absolute fecundity in both two species were
much lower than that in T zillii. It ranged from 428 to 5602 eggs for 0.
aureus, 680-1867 eggs for S. galilaeus while it ranged from 3135 to 7938
eggs for T zillii. Generally the absolute fecundity in cichlid species
increase progressively by increasing age and weight of gonads.
As regards to catch analysis in EI-Nozha hydrodrome during the
period of study (1998, 1999) it was observed that fishing operations carried out weekly during only four days with about 16 small fishing boats. Each
boat manned by two fishermen provided with gill and trammel nets. These
nets characterized by limited mesh size of not less than 80mm. The depth
of net ranged from 1.10-1.20 meters and length from 25-35 meter. The
period of fishing operation lasted for about 15 hours daily Annually, July
months is considered as the closing period for fishing.
During the period of investigation (1998), the number of fishing days
were 181 days, catch per trip ranged from 25kg to 111kg. The total daily
catch ranged from 345 kg in January to 1808 kg. in August. Species
composition of the catch revealed the presence of 13 fish species of which
cichlid fishes constituted about 63% of the total. Four cichlid species were
recorded in the catch namely : 0. aureus, S. galilaeus, T zillii and 0.
niloticus. 0. aureus dominated the catch of cichlid fishes by both weight
(54.0%) and number (51.0%) followed by S. galilaeus (weight: 25% &
number: 26.0%) and T zillii (weight 17.0% & number: 20%). 0. niloticus
was the least abundant species either by weight (3%) or number (4%).
Concerning the size composition of cichlid species, it was observed
that the size of 0. aureus varied between 12.0-33.0cm and the majority
ranged between 16.0-22.0cm forming about 78% of the total. For S.
galilaeus, it varied from 12.0 to 30.0cm and most of fishes ranged from
15.0-22.0cm constituting about 83% of the total. For T zillii the size varied
between 12.0-25.0 em and the dominant fishes had length range from 16.0-
19.0cm forming about 84% of its total catch. The populations of 0. aureus
and S. galilaeus were represented by five age groups (I-V) for each. Age
group II dominated the catch in both species forming 43% and 52%
respectively. For T zillii the population composed of four age groups from
I-IV and age group III dominated its catch (63%). The study of population dynamics of cichlid species showed that:
- T zillii have higher mortality coefficient (2 : 1.538) than S. galilaeus
(2 = 1.4842) and 0. aureus (2 : 1.1768) the reverse was found for
survival rate as 0. aureus had higher value comparing with the other
two species.
- T zillii had comparatively higher natural mortality (M= 0.76) than S.
galilaeus (M= 0.64) and 0. aureus (M= 0.64).
- S. galilaeus was observed to have higher fishing mortality and
exploitation rate. This was followed by T zillii and 0. aureus.
- Length and age at first capture were: 15.8, 15.6 and 16.0 ern for 0.
aureus, S. galilaeus and T zillii respectively. These were
corresponded to second year of life for the first two species while
it represented the third year of life for T zillii.
Recommendations:
Generally all cichlid species in El-Nozha Hydrodrome were not
subjected to overfishing and it is advised not to increase the exploitation
rate in case of S. galilaeus and T. zillii to prevent overfishing of these
fishes, since the yield per recruit at their Current yields nearly reached the
values of their maximum economic yield.
from the economic point of view, the regular supply of fresh water
from El-Mahmoudiah Canal into the basin is considered to be useful for
creating good environment for transplantation of 0. niloticus. Such
introduction of this species will increase the productivity of cichlid fishes
in the Hydrodrome as this species is characterized by higher weight as
compared with those of other cichlid species having the same lengths.