FULL LENGTH ARTICLE Aspects on the reproduction of eared horse mussel, Modiolus auriculatus (Krauss, 1848) in Red Sea, Egypt Fatma A. Abdel Razek a, * , Salah E. Abdel-Gaid b , Mohamed M. Abu-Zaid b , Tarek A. Aziz a a National Institute of Oceanography & Fisheries, NIOF, Egypt b Faculty of Science, Al-Azhar University, Cairo, Egypt Received 8 April 2014; accepted 28 April 2014 Available online 4 July 2014 KEYWORDS Reproductive cycle; Eared horse mussel; Modiolus auriculatus; Red Sea Abstract The reproductive cycle of the eared horse mussel, Modiolus auriculatus, was followed for one year from February, 2011 to January, 2012 based on 240 individuals collected from Hurghada, north coast of Red Sea, Egypt. The gonadal maturation of M. auriculatus was examined by means of macroscopic and histological preparations of the mantle. Annual cycle with periods of growth, maturity and discharge of gonadic products occurs simultaneously in both sexes. Ripe individuals were observed throughout the year. The largest number of spawning for the individuals occurred from March to June and July for the population. So, it was clear to identify one heavy spawning period for this species. Sexation of M. auriculatus did not differ significantly from 1:1. Sexes were distinguishable in all individuals at the ripe stage with a shell length greater than 3.00 cm. A direct positive correlation was observed between gonad index and water temperature. ª 2014 Hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries. Introduction Mussels have been a subject of great interest in recent years due to their increasing commercial importance. Most studies are related to the reproductive characteristics of the species widely distributed in temperate waters. Very little information exists with regard to tropical mussels (Cruz and Villaobos, 1993). Eared horse mussels of mytilidae are widely distributed in the world they occur in several seas of the tropical and sub- tropical regions. Modiolus auriculatus is a sedentary organism and is subjected to a wide range of environmental conditions. The interaction between reproductive processes and environ- mental changes may assume great importance for the well- being of the population. Nevertheless, few studies have been carried out on the eared horse mussels M. auriculatus in the Red Sea such as on bio- monitors for heavy metal levels (Hamed and Emara (2006); ecology and distribution Fshelson (1971), Oliver (1992) and * Corresponding author. Tel.: +20 1006620222. E-mail address: fatma_abdelrazek@hotmail.com (F.A.A. Razek). Peer review under responsibility of National Institute of Oceanography and Fisheries. Egyptian Journal of Aquatic Research (2014) 40, 191–198 HOSTED BY National Institute of Oceanography and Fisheries Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com http://dx.doi.org/10.1016/j.ejar.2014.04.003 1687-4285 ª 2014 Hosting by Elsevier B.V. on behalf of National Institute of Oceanography and Fisheries.