STOCK ASSESSMENT OF SOME IMPORTANT COMMERCIAL FISH SPECIES OF LAKE NASSER, EGYPT

Abstract

Due to the rarity of scientific information on Lates niloticus, A/estes dentex, Tilapia zillii, Oreochromis niloticus, and Sarotherodon galilaeus of Lake Nasser, the present work was suggested and aimed at:

i) Estimation of the biological and population parameters, age composition, length distribution and age-length key of the fore mentioned species.

ii) Studying and modeling population dynamics, stock assessment and fisheries status of those species, hoping that this work would be beneficial for researchers and design makers.

The present results can be summarized as follows:

Length-weight relationship of Lates niloticus, A/estes dentex, Tilapia zillii, Oreochromis niloticus and Sarotherodon galilaeus was best described by the general power function equations (W in g and SL in mm):

Lates niloticus A/estes dentex Tilapia zillii 0. niloticus 1984/1985

0. niloticus 1994/1995

0. niloticus 1999/2000

w = 6 X 10 -5 SL2.8246

W = 5 x 10 -6 SL3.232

w = 8 x 10 -5 s0.8958 w = 6 x 10 -5 s0.9414 w = 1 x 10-4 s0.804 w = 7 X 10 -5 SL2.9107 S. galilaeus 1984/1985

S. galilaeus 1994/1995

S. galilaeus 1999/2000

w = 2 X 10-4 SL2.7534

W = 5 x 10-4 SL2.5787

w = 2 x 10-4 sL2.7716

Test of significance of the exponent (n) led to the conclusion that the growth in weight relative to fish size was negatively allometric (n statistically less than 3) for all the forementioned species except for A/estes dentex where the growth in weight relative to fish size was positively allometric. There was no special trend in the condition factor of species studied with size increase.