Embryonic and larval development of a highly threatened killifish: ecological and conservation implications

Abstract

Anthropogenic habitat degradation and alien invasive species have led to the rapid decline of freshwater fish biodiversity globally. The knowledge of threatened species’ embryogenesis and larval development could be important for the design of appropriate conservation measures to reverse their decline. Here, we describe the embryonic and larval development of the globally threatened Peloponnese Valencia (Valencia robertae) to inform urgently needed ex situ and in situ conservation initiatives, such as safety stock creation, conservation translocation, and population monitoring. The development of V. robertae is described from the embryonic to the juvenile stage from in vivo imaging, for the first time in detail for this species and genus. Valencia robertae’s fertilised eggs are large (approximately 2 mm), spherical, macrolecithal, translucent, with negative buoyancy, filaments at the outer surface, and several oil globules. They have a long incubation period (approximately 18 days at 20 ± 1 °C) and, in laboratory conditions, a high hatching rate (84%, n = 89). Various types of chromatophores are visible in the embryo, incl. melanophores, xanthophores, and iridophores at the dorsal area of the eye and at the iris. Embryos at hatching measure approximately 5.4 mm SL (6.5 mm TL) and have well-developed caudal and pectoral fins, large eyes, and well-developed mouth; exogenous feeding starts at 24–48 h post hatching. Sequential formation of fins continues with the development of the anal and dorsal fins and is completed by the formation of the pelvic fins, at approximately 11 mm SL (25–30 days post hatching). The ecological and conservation implications of our findings are discussed.