The sense organs of teleost larvae are incomplete at hatching but sensory cells progressively recruit during development. Cutaneous respiration becomes inadequate after a time but gills then develop. Soon after larvae hatch, the simple segmental myotome system becomes complex and the red muscle concentrates in the midflank position. Median and caudal fin development can be related to the hydrodynamic regime in which the larvae move. Spontaneous activity as well as activity due to feeding, vertical migration, and depth holding increase with age. The feeding behaviour of larvae can be related to the perception of food, feeding success, volume of water searched for food and food requirements. These variables are linked in feeding models to the species, size, and distribution of food available. More complex feeding models incorporate energetic values of larva growth and food, nonrandom food distribution and search patterns of the larvae, and stochastic changes of variables. Predation models are less advanced but larva responses to predators are being investigated.