Mechanosensory Perception and Food Localisation in Pangasius nasutus Larvae: A Developmental Perspective

Patin fish (Pangasius nasutus) larvae hatch with immature morphological features, but as the larvae grow, all their sensory organs develop rapidly. The objectives of this study were to observe the behaviour of P. nasutus larvae and evaluate the development of their sensory organs. The larvae's behaviour was observed from the time of hatching, while the development of sensory organs was examined through histology and scanning electron microscope (SEM) analysis. This study demonstrated that changes in larval behaviour were influenced by the development of their sensory organs. During the initial stages, at Day 1 after hatching (DAH), most of the sensory organs were not yet fully developed. As a result, the larvae remained at the bottom of the aquarium and swam in a vertical direction. However, as the sensory organs started to develop, their behaviour changed. They became more active and began to swim horizontally throughout the aquarium, exhibiting phototaxis. The increased number of taste buds facilitated easier food detection, while the presence of free neuromasts enabled the larvae to respond to water movement, exhibiting rheotaxis at 3 DAH, the day of their first feeding. Furthermore, the development of other sensory organs, such as larvae's retina, at this stage enhanced their ability to navigate. The study found that larvae primarily use mechanosensory perception to locate food. This reliance is due to the earlier development of taste buds and olfactory organs compared to other sensory organs, with the sensory organ of P. nasutus taking 21 days after hatching to fully develop.