First information on biology of the needlefish Tylosurus acus imperialis (Belonidae) off the Tunisian coast (Central Mediterranean)

Sex ratio, age and growth, length and age at sexual maturity, and spawning season of the Mediterranean needlefish Tylosurus acus imperialis (Rafinesque, 1810) off Tunisian coast were investigated. A total of 126 individuals (54 females and 72 males) were sampled. The length weight relationships for females and males were W = 0.0027 L-2.832 (S.e.(a) +/- 0.004; s.e(.b) +/- 0.238) and W = 0.0026 L-2.827 (S.e.(a) +/- 0.002; s.e.(b) +/- 0.188), respectively. Otolith reading revealed that females belonged to age groups from 0 to 6 years and males from 2 to 4 years. Most of individuals were of age groups 3. The parameters of the von Bertalanffy growth function were L infinity=123.78 cm (s.e. +/- 17.93), k = 0.2 year(-1) (s.e. +/- 0.07) and t(0)= -2.28 year (s.e. +/- 0.57) for females and L infinity= 92.28 cm (s.e. +/- 5.93), k = 0.5 year(-1) (s.e. +/- 0.15) and t(0)= -1.16 year (s.e. +/- 0.45) for males. First sexual maturity was estimated at total length of 79.0 +/- 90.71 cm for females and 79.18 +/- 1.83 cm for males. Gonado-somatic index pattern indicated the spawning season extended from May to July.