Somatic growth, condition and form factor of Trachinus draco Linnaeus 1758 in the gulf of Tunis

Abstract

This study presents analyses about weight-length relationships, condition factor and form factor of Trachinus draco in the Gulf of Tunis. The fish samples were collected monthly from commercial landings of the soecues in the Gulf of Tunis between February 2014 to January 2015. The weight-length relationships of males, females and combined sexes exhibited a positive allometric growth. The lowest somatic growth was recorded in late summer and autumn for females but in winter for males. The somatic growth of females (W = 0.004 L3.136) was significantly different from that of males (W = 0.005 L3.077) with a better growth rate for the former. Biogeographical variations of the weight-length relationships of Trachinus draco are probably due to the different environmental conditions and food supply of each studied regions. The seasonal fluctuations of the condition factor of males and females, suggested a close relationship with the sexual cycle of the species. The mean condition factor (Kmean) of populations varied slightly higher as going from the Atlantic to the eastern Mediterranean basin and the Black Sea; a same gradual tendency was observed for the calculated median a3.0. value of the form factor. Then, condition factor and form factor may be used as sensible indicators for measuring environmental variations.