الفهرس 
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Abstract
The “Nile perch” Lates niloticus is an important food fish in tropical and semitropical waters. Lates niloticus is locally known as “Keshr Bayad” and is so far one of the most important economic species as food fish in Egypt and finds good marketing in the different parts of Egypt. During the last years with the development of industries and modern civilization, large amount of pollutants have been discharged into the Nile and the surrounding lakes. These pollutants not only affect the growth, health, and nutritional value of fishes but also the distribution (i.e., survival) and reproduction of economically important fishes. L. niloticus is one of those fishes, which were affected by environmental factors and its distribution was restricted only to Lake Nasser, Wadi El-Rayan, El-Salam Canal and sometimes the Nile River. On the other hand it disappeared from the most of north lakes i.e., Manzalah and Borollus and most of the Nile River. In spite of the extensive importance of Nile perch, it is somewhat surprising that such limited information concerning its reproduction is available. Thus, the present work was planned to carry out a detailed study of the reproductive processess of L. niloticus at different maturity stages during its reproductive cycle in natural habitat; Lake Nasser which is one of the most of its inhabit Lakes. Thus, the following points have been followed up:
I- Water quality.
II- Immunocytochemical identification of the hormone-secreting cells in the pituitary gland of Lates niloticus:
1- Adrenocorticotrops (ACTH cells).
2- Prolactin (PRL) cells.
3- Somatotrops (GH cells).
4- Gonadotropins (GTH Iβ and GTH IIβ) and thyrotropin (TSH)-secreting cells.
5- Somatolactin (SL) and α-MSH cells.
III- Immunocytochemical localization of GnRH forms in the Nile perch.
IV: Cyclic changes in mGnRH and GTH IIβ:
A. Immunostaining of mGnRH and GTH IIβ during ovarian maturation and spawning in female L. niloticus.
B. Immunostaining of mGnRH and GTH IIβ during testicular maturation in male L. niloticus.
* The results accomplished from this investigation are thereafter summed up:
Water salinity, sodium (Na), potassium (K), calcium (Ca2+), magnesium (Mg2+), phosphate (Po4), total dissolved salts (TDS), total hardness and conductivity values of El-Salam canal was significantly lower than that of Wadi El-Rayan water.
These findings lead to the conclusion that, the water quality; total dissolved salts (TDS), total hardness and conductivity affected the activity of the brain-hypophyseal-gonadal system of L. niloticus. Besides, the present results have urged and stimulated the need for further studies for optimizing the induced spawning technique of L. niloticus and improving its commercial applicability.