Age and growth of bogue, Boops boops, in Tunisian waters

Abstract

      The age and growth of bogue (Boops boops), collected in four areas off the Tunisian coast, were determined by studying growth marks on cross-sectioned otoliths. This calcified structure was chosen because the legibility and regularity of its growth mark patterns appeared to be more reliable than those of other skeletal elements. Opercula and fin rays were rejected because of intense bone remodeling, vertebrae because of numerous minute marks unrelated to cyclic events, and scales because counting of annuli seemed very unreliable, particularly in old specimens. Scales consistently had the highest average percent of error.

     Marginal zone analysis indicated that the hyaline zone in bogue otoliths was deposited yearly from November to April. Increase of length was determined and length-age data were fitted to Von BERTALANFFY equations. Comparisons of length increases of specimens from the four areas suggest two growth pools with greater increases in the north and east than in the Gulf of Tunis and the south. Relationships between growth and geographical distribution indicated the importance of environmental conditions especially water temperature and food availability, although the role of genetic and/or epigenetic factors could not be excluded.