Biometrical parameters and biological indices of the migratory species Conger conger (Linnaeus, 1758) from the northern coastal waters of Tunisia (Mediterranean Sea) / Paramètres biométriques et indices biologiques de l’espèce migratrice Conger conger (Linnaeus, 1758) des eaux côtières du nord de la Tunisie (mer Méditerranée)

Abstract

The European conger eel Conger conger represents an important economic resource. Previous studies have provided some information about the biometry of C. conger. This paper presents the first research on biometrical parameters and biological indices of this species in Tunisia. Our sample includes 353 specimens, among them 66.57% females, 32.29% of undetermined sex and only 1.13% males. The length and weight of specimens ranged from 25.5 to 135 cm and from 17.26 to 5087 g, respectively. For the meristic characteristics, the number of pre-pectoral pores was 6, the total number of pre-anal pores ranged between 44 and 47 and the total number of vertebrae varied between 148 and 154. Five allometric relationships were examined. The comparisons of slope and intercept show differences between individuals of determined sex (males and females grouped) and those of undetermined sex. Analysis of the weight-length relationship showed a positive allometric growth. Our data provided the first investigation on the seasonal variation of three bio-physiological indices ; the condition factor does not show variations among seasons, the gonadosomatic index variation reinforces the hypothesis that sexual maturation of C. conger females occurs during the migration from coastal waters towards spawning areas in the deep sea and the hepatosomatic index was highest in spring for females. Since C. conger is widely distributed in the Mediterranean Sea and the Atlantic Ocean, our contribution allows useful comparisons and clarifies the morphological and bio-physiological aspects of this species.