Otolith growth and age estimation of bastard grunt, Pomadasys incisus (Actinopterygii: Perciformes: Haemulidae), in the Gulf of Tunis (Central Mediterranean).

摘要

Background. Bastard grunt, Pomadasys incisus (Bowdich, 1825), is reported as a well-established species in the Mediterranean Sea. Although bastard grunt has rapidly expanded its area of distribution in the Mediterranean, there is no information about its age and growth. The aim of this study was to provide data about growth, condition, and first sexual maturity of the species in order to contribute to a better management of its fishery. Materials and methods. A total of 515 specimens of bastard grunt were caught in the Gulf of Tunis. The age was determined from otoliths. Length–weight relation, von Bertalanffy equation, and growth rate were employed to evaluate the fish growth. Also the condition factor and length at first sexual maturity were calculated. Results. In the Gulf of Tunis population, females were significantly predominant and the overall sex ratio (M : F) reached the value of 1 : 2.17. The two sexes showed a positive allometric growth. The marginal increment analysis validated the annual deposition of one single annulus in the winter. Growth in (total) length (TL) was approximately 65% during the first year of life. The von Bertalanffy growth equation was TL = 23.9 × (1 – e–0.186 × (t + 4.62)). The somatic condition of fish increased markedly during the late spring and summer. Length at first sexual maturity of the bastard grunt was 16.6 cm for males and 16.8 cm for females, which correspond to an age of about 2 years. Conclusion. The rapid growth during the first year of life, the early maturity and the moderately short life cycle contribute to the relatively fast spreading of the species.