الفهرس 
Nile Tilapia
MATERIALS AND METHODSOnly 14 pages are availabe for public view
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Abstract
Mohamed Mohamed Said Sayed: Estimation of Genetic Parameters for some Economic Traits in Nile Tilapia Oreochromis Niloticus. Unpublished Ph.D. Thesis, Department of Animal Production, Faculty of Agriculture, Ain Shams University, 2009.
The objectives of this study were to estimate the genetic and line crossing parameters for growth traits (weigth and length), condition factor (K), and tolerance traits for some enverionmental extrems (salinity and cold shock) in 30 day old Nile tilapia fry of four lins; Giza (G), Fouky (F), Mariout (M) and Nag-Hamaady (N). Heritabilities were estimated for growth rate (weight and length) condition factor, and response to some environmental extreme conditions; salinity tolerance (ST) and cold shock susceptibility (CS), the genetic and phenotypic correlations were estimated between the weight and length, in the four lines G, F, M and N. of early larval stages of Nile tilapia Oreochromis niloticus (30 days after hatching). Heritability estimates of weight, length, and condition factor were moderate to high for all studied lines; (0.18 - 0.85) for weight and length and (0.11 – 0.70) for the condition factor. Genetic and phenotypic correlations between weight and length were high (0.64 - 0.96). Heritability estimates of cold shock susceptibility were lower (0.13 - 0.22) than those for salinity tolerance (0.23 - 0.62). Line crossing analysis showed a generally highly significant effect for all line crossing effects, heterosis, general combining abilitiy (GCA), specific combining abilitiy (SCA), maternal abilility (MA), and sex linked effect (SL) concerning the weight; length; and condition factor. Overall heterosis for both weight and length were positive. ST and CS were significancantly affected by GCA, MA, SCA for both traits while ST was only affected by the sex linked effect (SL) with not significant effect and nigative estimte for the heterosis in the both traits.
Key Words: cold shock, condition factor, genetic and phenotypic correlations, growth rate, heritability, line crossing, salinity tolerance.