Ontogenetic Changes in Behavior and Sense Organ Morphogenesis in Largemouth Bass and Tilapia nilotica

The development of sensory systems and the coincident acquisition of associated behaviors were examined in two paternal brooders, largemouth bass Micropterus salmoides and Nile tilapia Tilapia nilotica. In newly hatched eleutheroembryos of largemouth bass, the eyes are unpigmented, the nares are closed, and the free neuromasts and taste buds are not developed. Six hours after hatching (when the epithelium of the otic vesicle is ciliated), the eleutheroembryos are able to aggregate by responding to the movements of neighboring siblings. Thereafter, four correlations between sense organ development and initiation of fish behavior were observed: appearance of the first free neuromasts on the head and positive rheotaxis; morphological completion of the larval-type retina and positive phototaxis; formation of twin cones in the retina and optomotor reaction; and appearance of taste buds in the oral cavity and selective feeding. The ontogenetic development of the sense organs of Nile tilapia reflects adaptations to early life in the parentˈs buccal cavity. The young of both species leave the custodial care of the parent when their sense organs become differentiated as adultlike forms.