Maritime Technology and Research 2022; 4(2): 254581 https://doi.org/10.33175/mtr.2022.254581 Maritime Technology and Research https://so04.tci-thaijo.org/index.php/MTR Research Article A comparison of the retinal structure in the zebra-snout seahorse (Hippocampus barbouri Jordan & Richardson, 1908) between juveniles and adults in captivity Ezra Mongkolchaichana 1 , Jes Kettratad 2 , Kitipong Angsujinda 3 , Sinlapachai Senarat 4,* , Pisit Poolprasert 5 , Natthawut Charoenphon 6 , Pattanasuda Sirinupong 7 , Supanut Pairohakul 2 and Koraon Wongkamhaeng 8 1 Department of General Education, Faculty of Science and Health Technology, Navamindradhiraj University, Bangkok 10300, Thailand 2 Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 3 Aquatic Resources Research Institute, Chulalongkorn University, Bangkok 10330, Thailand 4 Department of Marine Science and Environment, Faculty of Science and Fisheries Technology, Rajamangala University of Technology Srivijaya, Trang 92150, Thailand 5 Program of Biology, Faculty of Science and Technology, Pibulsongkram Rajabhat University, Phitsanulok 65000, Thailand 6 Department of Anatomy, Faculty of Medical Science, Naresuan University, Phitsanulok 65000, Thailand 7 Department of Science, Faculty of Science and Technology, Prince of Songkla University, Pattani 94000, Thailand 8 Department of Zoology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand Article information Abstract Received: September 23, 2021 Revised: November 15, 2021 Accepted: November 19, 2021 Keywords Eye structure, Histology, Photoreceptor cell layer, Seahorse, Juvenile, Thailand The activity of the sensory organ in the eye structure of the teleost fish is essential, as it plays an important role in regulating fish-feeding behaviors. Unfortunately, the above information in reference to the zebra-snout seahorse Hippocampus barbouri, an aquaculture species in Thailand, has not been described. In this study, the eye structure, together with the retinal structure, of juvenile [5 th and 20 th day after birth (DAB)] and adult (35 th DAB), H. barbouri reared in captivity was investigated. All DABs were carried out and histologically observed. Light microscopic level explored the external-lateral surface of the eye structure of H. barbouri, which consisted of the external, middle, and inner layers, as similarly reported in other teleost species. Well- differentiated retinal and photoreceptor cell layers were observed at 35 th DAB compared to that of other DABs. This finding supports feeding strategies in captivity, helping the Thailand “circular aquaculture” of this fish. 1. Introduction The eye of fish is considered to be the major visual system and serves as an important sensory organ to support mating, feeding, and predator avoidance (Genten et al., 2008; Yokoyama & Yokoyama, 1996; Bowmaker, 1991). The anatomy and histological structure of the eye is an important topic in several fishes (Perez et al., 2017; Boonyoung et al., 2015; Senarat et al., 2013; Genten et al., 2008). The remarkable retinal layer of most fish includes the neuron and neuronal * Corresponding author: Department of Marine Science and Environment, Faculty of Science and Fisheries Technology, Rajamangala University of Technology Srivijaya, Trang 92150, Thailand E-mail address: sinlapachai.s@rmutsv.ac.th Maritime Technology and Research 2022; 4(2): 254581