One-year field study measures golden grey mullet reproduction and growth in Tunisia’s Bizerte Lagoon

A one-year field study of golden grey mullet, Chelon auratus, in Tunisia’s Bizerte Lagoon found an October–December reproductive period, slightly larger female maturity size, negative allometric growth and an observed age range of one to six years. The study characterized the lagoon population but did not establish long-term population trends.

Researchers collected 576 fish monthly from January through December 2022 at Menzel Abderrahmane harbor using a trammel net with 26–60 mm diamond mesh. They measured total length, total and eviscerated body weight, and gonad and liver weights, classified gonadal maturity, assessed sex ratio and condition, and examined scales from all 576 specimens for age estimation.

The sample comprised 290 females and 286 males, corresponding to approximately 1.01 females per male and an approximately balanced overall sex ratio. A chi-square test found no significant difference between the sexes (χ² = 1.25, degrees of freedom = 1, P > 0.05). Females predominated in January, April and November and among fish longer than 26 cm, except in the 32- and 33-cm length classes.

Logistic estimates placed total length at 50% maturity at 23.46 ± 0.2 cm for females and 22.5 ± 0.18 cm for males. Both sexes reached sexual maturity during their second year of life. Gonads began developing after August, and the gonadosomatic index peaked in October at 9.5 ± 0.7 for females and 5.64 ± 0.58 for males before declining in December, supporting a reproductive period from October through December.

Fecundity was measured in 45 ripe females caught in September, October and November. Absolute fecundity ranged from 115,000 to 500,000 oocytes, with a mean of 256,867 ± 98,134 oocytes and a 95% confidence interval of 220,000–293,700. Relative fecundity averaged 1,233 ± 143 eggs per gram of body weight, with a 95% confidence interval of 1,150–1,316 eggs per gram.

Length–weight relationships indicated negative allometric growth. The exponents were 2.6071 for females, 2.707 for males and 2.6875 for both sexes combined, each significantly below 3. Scale analysis suggested one growth ring per year, with the highest mean marginal increment in October. Fish sampled spanned one to six years, and most belonged to the three- and four-year classes; the maximum observed age was six years.

Observed and back-calculated growth curves were similar. For combined sexes, a von Bertalanffy model fitted to observed length-at-age data estimated asymptotic total length of 44.25 cm and a growth coefficient of 0.179 per year. Growth performance was similar between females and males, with indices of 2.55 and 2.53 cm per year, respectively, and the growth rate did not differ significantly between the sexes. Model-based theoretical longevity was estimated at 15.23 years for females and 14.89 years for males, rather than the six-year maximum observed in the sample.

The research was limited to one lagoon and one annual sampling period, so its observations and model estimates provide a local baseline rather than evidence of temporal change. The authors stated that broader spatial and temporal monitoring, combined with environmental and genetic data, would be needed for a more comprehensive assessment.

Subject of Research: Reproductive biology, age structure and growth of golden grey mullet in Bizerte Lagoon

Article Title: Reproductive and growth parameters of Chelon auratus ( Actinopterygii , Mugiliformes , Mugilidae ) in Bizerte Lagoon, Tunisia

Article References: Hajlaoui, W., Mili, S., Ennouri, R., Sessi, H., Mahmoudi, E., Hedfi, A., Ben Ali, M., & Missaoui, H. (2026). Reproductive and growth parameters of Chelon auratus (Actinopterygii, Mugiliformes, Mugilidae) in Bizerte Lagoon, Tunisia. Acta Ichthyologica et Piscatoria, 56, 63-75. https://doi.org/10.3897/aiep.56.175000

Image Credits: AI Generated

DOI: 10.3897/aiep.56.175000

Keywords: golden grey mullet, Chelon auratus, Bizerte Lagoon, fish reproduction, fish growth, maturity size, fecundity, age estimation, Tunisia, fisheries biology, Reproductive, growth