A study on growth, mortality and a biochemical growth indicator of Oreochromis niloticus in a Nile Canal, Egypt.

Abstract

Molecular bioindicators Growth Mortality RNA/DNA This study was carried out to examine growth and mortality and the efficiency of the ratio of RNA/DNA in characterizing growth of Oreochromis niloticus. Growth in weight with length of fish was predicted by the significant relationship: Log W (g) =-1.6696 + 3.1971 log L (cm). The value of the slope of that relationship was found to be the highest, when compared with other reported values in different localities, where rise in temperature in the period of study is suspected. The fish under study were found to fall in 5 age-groups. Seasonal variation of the condition coeffecient "K" showed a slight decrease on going from winter towards summer. The instantaneous total mortality was predicted as 1.4022, and consequently survival rate was 0.2461 and mortality rate was more than 75 %. The lower value of survival rate than that earlier reported study, was thought to be due to rise in temperature because of global warming. The ratio of RNA/DNA increased with increase of either age or length of fish, but declined at age V, corresponding to the length of 24 cm. This finding could be attributed to the effect of fishing recruitment which is covering the first 4 age-goups. Significant relationship between RNA/DNA and K (r 2 = 0.78), then with seasonal variation (r 2 = 0.81). Those relationships showed a rise in the molecular ration, and K, during winter and decline in summer could be speculated as a compensation in growth after disturbance in growth during spawning period. Thus, the RNA/DNA ration variation could be tied to describing growth of O. niloticus, as well as seasonal variation effects.