Analysis of the Biological Features of the Blue Tilapia, <i>Oreochromis aureus</i> in the Garmat Ali River, Basrah, Iraq

Abstract

The blue tilapia, Oreochromis aureus (Steindachner, 1864) is exotic fish and became widely distributed throughout different natural waters of Iraq during the last years. The present study describes the length compositions, age, growth, reproduction and food habit of the species in the Garmat Ali River from September 2018 to August 2019. A total of 1050 specimens were caught using gill nets, cast net, and electro-fishing. The lengths of O. aureus ranged from 6.6 to 22.9 cm, and the most dominant lengths were 14.0 to 18.0 cm representing 61.6% of the catch. A positive allometric growth pattern was observed for males (b= 3.317), females (b= 3.231) and all individuals (b= 3.283). There were three peaks for relative condition factor (Kn) that appeared during October, April, and July for both sexes. The age estimated on the basis of scales showed that the population comprised of 1 to 5 years. The parameters of the von Bertalanffy growth curve were L∞= 27.6 cm, K= 0.193 and to= 1.18. The growth performance index (ø) of O. aureus was computed as 2.17. The overall sex ratio (male: female) was1:1.04. Females attained sexual maturity at a lower size than males with mean size at first maturity determined as 6.6 cm for females and 9.2 cm for males. Two peaks of the gonado-somatic index were shown, the higher one in April and the lower one in September in both sexes. The estimated fecundity ranged from 352 to 1033 eggs in the fish ranging from 12.2 to 20.5 cm in length. O. aureus is an opportunistic feeder that will successfully utilize whatever food source is available, its diet comprised of detritus (43.1%), diatoms (23.9%), algae (22.8%), macrophytes (7.1%) and crustaceans (6.0%). The results highlighted basic biological features on invasion fish species which can assist in fisheries management and conservation of the fish species in Iraqi waters.