DEVELOPMENT OF THE VISUAL-SYSTEM AND INFERRED PERFORMANCE CAPABILITIES OF LARVAL AND EARLY JUVENILE SCOMBRIDS

Development of the visual system in larval and early juvenile Euthynnu s lineatus, Auxis spp., and Scomberomorus sierra was examined histolog ically. First-feeding larvae of all three taxa possess a pure cone ret ina, with theoretical acuities ranging from 50 min of are in Scomberom orus sierra to about 60 min of are in Euthynnus lineatus and Auxis spp . Accommodative structures (lens retractor muscle and suspensory ligam ent) first appear during the late preflexion stage. Rod precursors app ear in the flexion and early postflexion stages. By the late postflexi on stage, the appearance of retinomotor movements indicates functional ity of rods. The optic tectum is prominent in the midbrain at the firs t-feeding stage and exhibits rapid growth and differentiation. The tor us longitudinalis, an important sensory integration center of the tect um, does not develop until the early postflexion stage. Development of the visual system in larval scombrids is advanced and is likely invol ved in rapid improvements in foraging abilities and piscivory.