Assessment of two cichlids stocks with virtual population analysis in Garmat Ali River, Basrah, Iraq

Mohamed Abdul-Razak Mahmood Mohamed Abdul-Razak Mahmood

doi:10.30574/wjarr.2022.13.2.0134

Abstract

The study is an attempt to evaluate the population characteristics and virtual population analysis (VPA) of two invasive species (Oreochromis niloticus and Oreochromis aureus) using the FiSAT II software based on the data collected from the Garmat Ali River, Iraq. A total of 4391 individuals (2727 of O. niloticus and 1664 of O. aureus) were measured for length-frequency analysis from October 2019 to September 2020. Length-weight relationships were derived, indicating allometric growth for both species. The asymptotic length (L∞) and growth rate constant (K) were estimated to be 30.5 cm and 0.45 for O. niloticus and 29.9 cm and 0.21 for O. aureus. The annual rates of fishing (F) and exploitation (E) for O. niloticus were found to be 2.24 and 0.69, respectively, and for O. aureus 0.48 and 0.43, respectively. The present exploitation rates (E) of both species were below the biological target reference points, E0.1 and Emax, thus expressing a case of under-exploitation of both species. Besides, the result of the virtual population analysis (VPA) revealed that the majority of O. niloticus and O. aureus individuals were harvested at lengths 20 cm and 17 cm, respectively. Also, the lengths at first capture (L50) for both species were considerably higher than their lengths at first maturity (Lm). Therefore, for management purposes, this study suggests that more yields can be obtained by increasing the fishing activities on these invasive species, such as increasing the number of fishing boats and decreasing the mesh size to decline its abundance in the long term.

Highlights

The Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) and the blue tilapia, Oreochromis aureus (Steindachner, 1864) are members of the Cichlidae family
Cichlids species are invasive fish to Iraqi waters, and early records show that Coptodon zillii caught from the Euphrates River, middle of Iraq during 2007, later other species, O. aureus and O. niloticus documented in the south of Iraq
Fish sampling A total of 2727 individuals of O. niloticus and 1664 individuals of O. aureus were collected monthly from two sites on the river, the first site is located near Al-Najeebia Bridge opposite the site of the Naval Academy and the second site is located at the upper river before its confluence with the East Hammar marsh (Fig. 1) during October 2019 to September 2020 [18]

Summary

Introduction

The Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) and the blue tilapia, Oreochromis aureus (Steindachner, 1864) are members of the Cichlidae family. Cichlids species are invasive fish to Iraqi waters, and early records show that Coptodon zillii caught from the Euphrates River, middle of Iraq during 2007, later other species, O. aureus and O. niloticus documented in the south of Iraq. These three species are well established and dominate the fish populations in various Iraqi waters [4,5,6,7,8,9,10,11,12,13]

Methods

Results

Conclusion