Evaluation of biological characters of the invasive species, Coptodon zillii in the Garmat Ali River, Basrah, Iraq

Abstract

The age, growth, reproductive biology and food habit of the invasive Redbelly tilapia (Coptodon zillii) from Garmat Ali River, Iraq. The length-weight relationship was W= 0.009*L3.237 for fish of 7-22 cm, indicates positive allometric growth. The mean values of the relative condition factor were 1.01 and 1.02 for males and females, respectively, indicate a healthy condition of fish. Five age groups were obtained, and their lengths were 9.0, 12.0, 14.6, 16.6 and 18.5 cm, respectively. The growth model parameters were L∞= 28.4 cm, K= 0.168 and to= -1.279, and the growth performance index (Φ) was 2.13. Sex ratio (male: female) was 1:0.81, which deviates from the normal ratio. Length at maturity was 8.2 cm (males) and 8.4 cm (females). Gonadosomatic index (GSI) values ranged between 0.06 in August and 1.89 in July for males and 0.04 in July and 5.35 in April for females indicate that the spawning season extended from April to June. Fecundity varied from 1635 to 3072 eggs for fish of 11.2-17.1 cm. The fecundity (F) can be estimated with the formula F= 75.89 * L1.26 or F=424.24 * W0.41 (L= total length and W= body weight). Feeding intensity and activity of C. zillii were high during spring and summer, respectively. The species fed mainly on detritus (44.6%), algae (19.9%), macrophytes (19.7%) and diatoms (13.3%). These results can assist in fisheries management and conservation of the fish species in Iraqi waters.