The biology of Oreochromis niloticus in a polluted canal.

In the present investigation, length-weight relationship, condition factor, age, growth, mortality, gonadosomatic index (GSI) and fecundity of tilapias (Bolti in Arabic): Oreochromis niloticus, from Shanawan drainage canal (SDC), Al-Minufiya Province, Egypt, were studied. This was carried out on 162 fish samples collected during the period from April 1992 to May 1993. Oreochromis niloticus was found to attain sexual maturity early (8-9 cm), was more fecund (1,234-3,893) and has high mortality rates (91% for males and 94% for females). A comparison of the various parameters of O. niloticus from SDC with those of other authors in different localities and times in Egypt revealed year-to-year and geographically significant differences in relation to variation in weight with length, condition factor, fecundity, growth and mortality rates. These differences were discussed and were found to be attributed to the effect of eutrophication and pollution on the growth, age and other biological aspects of O. niloticius. Multiple regression analysis showed that only female GSI correlated significantly with pesticides and heavy metals contamination.