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Bayesian Growth Modeling and Length-Based Indicators: Stock Assessment of Nile Tilapia (Oreochromis niloticus) in Lake Nasser, Egypt
by
, ,
Manar Abdellatif
1
,
Richard Kindong
1,2,3,4,5,*
,
Khaled Y. AbouelFadl
6 and
Siquan Tian
1,2,3,4,5,* 1
College of Marine Living Resource Sciences and Management, Shanghai Ocean University, Shanghai 201306, China
2
National Engineering Research Centre for Oceanic Fisheries, Shanghai 201306, China
3
Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education, Shanghai 201306, China
4
National Data Centre for Distant-Water Fisheries of China, Shanghai 201306, China
5
Key Laboratory of Oceanic Fisheries Exploration, Ministry of Agriculture and Rural Affairs, Shanghai 201306, China
6
Faculty of Fish and Fisheries Technology, Aswan University, Aswan 81628, Egypt
*
Authors to whom correspondence should be addressed.
Biology 2026, 15(11), 868; https://doi.org/10.3390/biology15110868 (registering DOI)
Submission received: 21 April 2026
/
Revised: 21 May 2026
/
Accepted: 25 May 2026
/
Published: 31 May 2026
(This article belongs to the Section Marine and Freshwater Biology)
Simple Summary
Nile tilapia is a major species in Lake Nasser and a significant source of food and income in Egypt. However, its stock status remains poorly assessed because of limited biological data. In this study, we combined age validation, growth estimation, maturity analysis, and length-based indicators to assess the status of the fish population. The results showed a negative allometric growth pattern, maturity at around 2 to 2.5 years, and a lifespan of up to 5 years. Many fish are caught before they reach maturity, and the catch lacks enough mega-spawner individuals, as indicated by length-based indicators. These findings suggest that the stock is overexploited and faces severe fishing pressure. Our integrated age- and length-based approach provides a robust stock status framework for helping fisheries managers and supporting their actions to rebuild the stock fishery and ensure long-term sustainability.
Abstract
The present study incorporates age- and length-based methods to estimate the stock status of Nile tilapia (Oreochromis niloticus) in the inland fisheries of Lake Nasser, Egypt. In 2021, a total of 570 specimens were sampled to determine the length–weight relationships, condition factor, maturity schedules, age structure and growth parameters. The age estimations were quite accurate, suggesting a lifespan of 5 years. Females attained 50% maturity at a length of 27.85 cm and age of 2.30 years, while males attained maturity at 29.93 cm and 2.45 years. The von Bertalanffy model best described growth parameters using the Bayesian approach. Length-based reference points produced from aLBI indicate a close association between length at initial maturity (Lmat = 29.3 cm) and optimal harvest length (Lopt = 30.8 cm). The Froese indicators indicate that all the proportions of mature fish (Pmat = 44.8%), fish of optimum size (Popt = 35.6%), and big spawners (Pmega = 18.1%) were below sustainability targets. The results indicate that non-selective fishing gear is responsible for growth and recruitment overfishing by harvesting fish at, or below, maturity. The integrated Bayesian–aLBI approach offers a rigors and transparent assessment for inland fisheries with limited data and support for size-based management actions to rebuild the Nile tilapia stock in Lake Nasser.
