الفهرس 
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Abstract
.:. Siganids, rabbit fish, marbled spine foot fish locally named ”Batata” are
a group of marine fish originally belong to Indopacific waters and
represented in Red Sea by five species out of20 from genus Siganu.l .
•:. While Suez Canal was opened to connect Mediterranean Sea with Red
Sea during 1869, two species of Siganus could immigrate to live in
eastern Mediterranean waters viz. Siganus rivulatus and Siganus
luridus which are the main topic of the present study .
•:. Genus Siganus is comprising nearly 0.56% of the total annual catch of
marine waters in Egypt. This amount of fish landing could be doubled if
proper measures may be taken toward capture and culture fisheries .
•:. In the present study, almost 1134 fish from S. rivulatus and 324 fish of
S. luridus were sampled to conduct various aspects of biological
investigations. The samples were representing the fish catch from the
coastal zone area off Alexandria and marketed in the two main fish
markets; Alanfoushy for the west side of the city and Abu Qir for the
east side of it.
.:. Samples collected here ranged between 11-28 em and 17-238 gin
length and weight, respectively, which covered one year time from
March 1994 to February 1995 for both studied species: S. rivulatus and
S. luridus. The former is de facto more common than the latter.
.:. s. rivulatus and S. luridus proved to be herbivorous fish thrive best
during summer season, while in winter feeding coefficient becomes less
as per fullness coefficient and emptiness coefficient.
.:. Selectivity index showed that plant origin material is more selected food
item while the feeding intensity or filling index was also high in summer
less in winter. Hepatosomatic index has supported the same observation
in both species .
•:. Gut content analysis conducted by occurrence and points method
showed that plant origin material was dominant represented by mostly
Chlorophyceae. Plant origin material contributed 94% and 91% by
composition. On the other hand, other food items comprise 6% and 9%
only in case of S. rivulatus and S: luridus, respectively .
•:. The index of preponderance of food items as a combination of
employed methods proved exactly that plant origin material occupies
99% or 98.3 as the first rank while other food items consist only I% or
1.7 for S. rivulatus and S. luridus, respectively .
•:. Age and growth of S. rivulatus was studied for age assessment: two
graphical methods and two indirect employing hard parts. Petersen
method was supported by Harding-Cassie plot and the length frequency
in both methods revealed the presence of five modes representing age
class from one to five similarly for S. luridus.
.:. Vertebrae were employed for age assessment and the relation between
vertebral radius-fish length manifested that four age groups were
recorded and the corresponding lengths were also calculated .
•:. Eye lens weight was used to evaluate the age and hence the growth of
S. rivulatus is calculated. In this method, the relationship between eye
lens weight and fish length pointed out towards the same results in
which S. rivulatus here were sampled from five age groups and similar
results were obtained for S. luridus .
•:. Length-weight relationship was determined and the equation was:
log W = -1.866 + 2.872 log L for S. rivulatus. Perusal of the results
proved also that, condition factor ”K” was increased during summer and
decreased in winter, which is related to food abundance and the
spawnmg season. The equation for S. luridus was: 10 W = -1.821 +
2.881 log L.
.:. Growth increment in length and weight was calculated to be 1195.
15.81, 18.59 and 21.25 cm for length increment for S. rivulatus. The
age class of one year to four years, on the other hand weight increment
for the same year classes were 19.49, 23.89, 25.79 and 32.26 g,
respectively. The maximum length theoritically is 32 em as Von
Bertalanffy growth equation represented by Ford Walford. In case of S.
luridus, the length recorded at 11.84, 15.75, 18.55 and 21.12 em,
respectively for the first till the fifth year of life while the annual weight
increment recorded against these figures were 18.68,23.82,25.59 and
30.87 g, respectively. The maximum length is 30 em as per used
equation of Ford-Walford.
.:. s. rivulatus has sex ratio ill which females commonly outnumbered
males as 1 : 1.30, while for S. luridus sex ratio was less (1: 1.17) and the
gonadosomatic index was higher during May-August and the length or
weight of gonads tend to increase while fish size increases .
•:. Seven maturity stages were described and the size at fish gains its
maturation was determined at 18-19 em of fish length or at the end of its
second year oflife .
•:. Ova size ranged between 0.4 to 0.7 mm for ripe stage and the female
releases ou: patch of eggs during the spawning season of 0.7 mm ova
size and the spawning season of S. rivulatus as revealed by maturity
stages as gonadosomatic appears to be during summer in between May-
August and its peak falls in June and for S. luridus as well .
•:. Fecundity of S. rivulatus is ranging between 283.569 to 865.377 while
it is 14.924 to 30.906 as absolute and relative, respectively. The
equation for the absolute fecundity was:
log Fa = 1.8087 + 2.8256 log L or log Fr = 1.7707 + 1.8533 log L
for the fecundity count related to length, while it was:
log Fa = 3.7720 + 0.887310g W or log Fr = 3.7681 - 0.1106 log L
for the fecundity related to weight. Fecundity always increases with the
corresponding increase in fish size .
•:. Siganids could boost the production rate of fishes both ways capture
and culture fisheries, since the fish has acceptable growth rate and high
fecundity as well as it thrive best on sea weeds and plants. The fish
normally inhibit the off-shore waters which can be utilized with
reasonable measurements.