Kinematics of prey capture and histological development of related organs in juvenile seahorse

Abstract

The seahorse is a typical suction feeder with an elongated, tubular snout and a small terminal mouth. It is important to determine the details of this unique prey-capture behavior to improve the survival rate during seahorse breeding, especially for juveniles. In this study, we described the sucking process and characterized the kinematics in juvenile lined seahorse (Hippocampus erectus) at different ages (1–30 days after parturition; DAP) using a high-speed video system, and also investigated the histological basis of the feeding-related organs, including snout, eye, and intestine. The sucking of juvenile seahorses can be divided into four steps: searching, locating, capturing, and swallowing. Seahorses capture prey mainly based on the vision system, and histological results revealed a developed visual acuity in the newborn seahorses, so that they were able to prey once after releasing from the male seahorse's brood pouch. The attack distance, maximum snout width, capture success rate, and daily food intake of juvenile seahorses increased with maturation. A remarkable inflection point, in the snout expansion rate, successful predation rate, and growth rate, occurs at about 10 DAP, when calcification of the snout bones was completed. In addition, the intestines of newborn seahorses were short and quite simple, but developed rapidly during the first 20 DAP. These findings provide a better understanding of prey capture kinematics and nutritional physiology, and will be beneficial for improving the feeding strategies for juveniles during large seahorse breeding.