Development of the lateral line system in the rostrum of the paddlefish

The rostrum of the paddlefish ( Polyodon spathula ) develops over a short period soon after hatching. The mechanosensory lateral line system includes two canals that run the length of the rostrum and feature numerous neuromasts. The rostrum canals connect with the external environment via a series of accessory canals that open to the rostrum's ventral surface. Thus, these fish are an interesting model for sensory development and integration. The goal of this study was to further the understanding of the development and function of the rostrum. We compared the number of, and the distance between, accessory canals in the rostrum of paddlefish at four developmental stages. After bleaching of 10% NBF‐preserved fish, external application of India ink was used to fill the rostrum lateral line system. Each filled rostrum was imaged and accessory canal numbers and inter‐accessory canal distances were assessed using image analysis programs (ImageJ and GIMP 2). Data indicate that the number of accessory canals and the inter‐accessory canal distances both increased as development proceeded. These results suggest that the two main lateral line canals elongate with rostrum growth via distal extension and elongation of inter‐accessory canal segments. This work indicates that neuromast proliferation in the rostrum lateral line canals would be an interesting subject for further study.