الفهرس 
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Abstract
The red swamp crayfish, Procambarus clarkii (Girard, 1852) (Decapoda, Cambaridae), is a native species in the southern and central regions of the United States. It was introduced into the River Nile in the early 1980s and has become a resident in the Egyptian freshwater ecosystems, but up till now no detailed study has been done to know its stock or even its population dynamic in the River Nile.
The population dynamical parameters of Procambarus clarkii were estimated based on 3465 specimens (1455 males and 2010 females) (7.0 – 15.0cm TL), collected from two locations along the River Nile; from 2009 to 2012.
Length frequency analysis was used for age determination of the animal from river Nile by applying the Bhattacharya method and ELEFAN I software. The population ranged between 7 and 13.8 cm TL (3.5 – 7.4 cm CL) for males from 7 to15 cm TL (3.5 – 8 cm CL) for females.
By applying the Modal Progression Analysis (MPA) and ELEFAN I, it is obvious that, the longevity extends one year for males and one and half years for females.
It is also observed that, the most dominant age group for males was the second age group representing 68% of the total male specimens. In addition, the most dominant age group for female specimens was the second age group representing 54.6% of the total female specimens.
The basic age-length data obtained by means of MPA and ELEFAN I were used for studying the growth pattern and show that this species attains its highest growth rate during the first six months of life.
The equation relating CL and TL for males and females are:
Male: W= 0.0218 L3.1910 (males)
Female: W= 0.0233 L3.0999 (females)
Sexes combined: W= 0.026 L3.0804 (combined sexes)
The obtained growth parameters (L∞, K and to) are the basic input data into various models used for managing and assessing the status of the exploited stocks.
The obtained values of growth coefficient “K” were relatively high indicating the high growth rate.
The growth performance index (Ø’) for the animal in the River Nile is 3.2, 2.7 and 3.19 for males, females and pooled data respectively.
The curve derived from the catch curve provided an estimate of length at first capture (Lc) was 9.11 and 9.25 cm for males and females respectively. These values were corresponding to ages (Tc) of 7 and 8 months for males and females respectively.
In the present work, two methods were used for the estimation of the total mortality coefficient (Z) Linearized length converted catch curve was 3.65, 5.6 and 5.21 for males, females and pooled data respectively.
The geometric mean of natural mortality coefficient (M) by the same methods was 2.28, 1.91 and 1.99 per year for male, female and sexes combined respectively.
The fishing mortality coefficient (F) was 1.37, 3.69 and 3.22 per year for males, females and sexes combined respectively. The obtained results indicated that the fishing mortality coefficient of females is higher than that of males.
The exploitation ratio (E) was 0.38, 0.66 and 0.62 per year for males, females and sexes combined respectively. This results indicating that females are more vulnerable for fishing activities than males.
The relative yield per recruit (Y’/R) and relative biomass per recruit (B’/R) analysis gives a maximum (Y’/R) at E= 0.70 and the exploitation level which maintains the spawning stock biomass at 50% of the virgin spawning biomass E0.5 was 0.37.
On the other hand, the ovary of P. clarkii consists from two ovarian lobes run anteriorly and a third one runs posteriorly. The size and colour of the ovary of P. clarkii is changing during its maturation, as in the early stage is small with whitish yellow colour, while in the middle stage is medium sized with yellowish orange colour, and in the late stage is large in size with dark brown colour.
Histologically, the early ovarian developmental stage is characterized by the presence of small oocytes which are elliptical in shape. The next stage is a vitellogenic stage which spherical in shape. Later vitellogenic oocytes lose their round shape and appear squarish. The ovarian development of P. clarkii is completed by the formation of mature stage of oocyte which become larger in size.
Male reproductive system of P. clarkii consists from trilobed testis with two lobes located anteriorly then unite together posteriorly forming one median lobe. Lobes are white in colour and are connected together by three collecting ducts one from each lobe. Both vasa deferentia run posteriorly and open into male gonopores.
Histologically, The testis of the animal is composed of numerous seminiferous tubules; which include various developmental stages of germ cells. In mature testis, the spermatogonia cells divide meiotically, and develop into primary and secondary spermatocytes then spermatids. Eventually spermatids differentiate into mature sperms.
In conclusion, the relative yield per recruit (Y’/R) and relative biomass per recruit (B’/R) analysis for P. clarkii in the River Nile gives a maximum (Y’/R) at E= 0.70 and the exploitation level which maintains the spawning stock biomass at 50% of the virgin spawning biomass E0.5 was estimated at 0.37. So, keeping the exploitation ratio at its current value or reducing it to E0.5 value (E= 0.37) will achieve more economic return.
Also, the study revealed that the reproductive capacity of P. clarkii continues all the year round, where two to three generations can be produced each year in the Egyptian water with maximum spawning seasons in the fall (late September- October) and during Spring . Therefore, it is recommended to stop commercial fishing of the crayfish during these seasons.