Development and Seasonal Variations of the Larvae of Three Mesopelagic Fishes near Coral Reefs in the Red Sea

This work aims to describe the larval stages and the seasonal variation in the abundance of three mesopelagic species whose larvae are surprisingly abundant near coral reef areas in the Red Sea. The larvae were collected monthly using a plankton net (500 µ) from three coastal coral reef areas surrounding Sharm El-Sheikh on the Egyptian Red Sea coast between January and December 2015. The identification of larvae was based on the morphological and meristic characteristics according to the available literature. The larvae of this species were divided into preflexion, flexion, and postflexion stages and they were also categorized according to their size into relevant size classes. Mesopelagic fishes were represented in the collection by four species belonging to four families: Vinciguerria mabahiss (Family: Phosichthyidae), Benthosema pterotum (Family: Myctophidae), Astronesthes martensii (Family: Stomiidae; subfamily: Astronesthinae), and Trichiurus sp. (Family: Trichiuridae). In general, a total of 3678 larvae were collected, of which 1191, constituting about 32% of the total fish larvae, belonged to mesopelagic species. The most abundant species was V. mabahiss, with 677 larvae that constituted 18% and 57% of the total larvae and mesopelagic fish larvae, respectively. The second most abundant species was B. pterotum, which was represented by 485 larvae (13% of the total larvae and 40% of the mesopelagic fish larvae). A. martensii was represented by the lowest number of larvae (29 larvae, 2%). Most larvae of the three species were small and in the preflexion stage, whereas larger larvae are absent. They are highly abundant in the cooler months of the year between November and April. The high number of preflexion larvae may indicate that the three mesopelagic species spawn in the colder times of the year.