Population Structure and Stock Assessment of Tilapia Species in Coastal Lagoon, Lake Manzala, Egypt

This study aimed to estimate the biology and population structure of cichlid species in Lake Manzala, where tilapias are the main catch. Samples were collected from commercial fishing boats in the fishing areas between 2019 and 2021. The length frequency distributions were evaluated using FiSAT II software. The results showed that Oreochromis niloticus was the most dominant species, making up 50% of the tilapia catch. Four age groups were found in O. niloticus and Coptodon zillii, and three in Oreochomis aureus and Sarotherodon galilaeus. Age group II was the most dominant across all species. The von Bertalanffy equation constants (L∞ & K) were 26.25 cm & 0.47y-1 for O. aureus, 30.45 cm & 0.58y-1 for O. niloticus, and 16.80 cm & 0.70y-1 for C. zillii, and 24.15 cm & 0.36y-1 for S. galilaeus. The length at first capture (Lc) was around 14.0 cm for most species, except for C. zillii (8.0 cm). Exploitation rates (E) were 0.58, 0.71, 0.55 and 0.59 for O. aureus, O. niloticus, C. zillii, and S. galilaeus, respectively. The study concluded that tilapia fisheries in Lake Manzala are experiencing over-exploitation. To achieve management in the area of study, the current level of exploitation needs to be controlled by reducing fishing effort.