Quantitative changes in the otolithic organs of the inner ear during the settlement period in European hake Merluccius merluccius

Qualitative and quantitative observations were made of the density and growth of the sensory epithelia, hair cell number, and otoliths of the 3 pairs of end organs (saccule, lagena, and utricle) of the inner ear of European hake Merluccius merluccius (35 to 100 mm length) caught in the northwestern Mediterranean Sea. This is the period in the hake’s life-history during which the transition from pelagic to epibenthic forms (settlement period) occurs. The results demonstrate a quantitative inversion in the percentage of the sensory epithelia area and the number of hair cells between the saccule and utricle over this time period. This period is also coincident with the settlement period that takes place when most individuals are ca. 50 mm, at which time the fish become epibenthic. These quantitative changes in the ear could be related to ecological changes in mobility and feeding.