Reproductive biology and embryonic and larval development of the "cardinal tetra", Paracheirodon axelrodi Schultz, 1956 (Characiformes: Characidae), in laboratory

Abstract

Paracheirodon axelrodi, or "cardinal tetra" is an important ornamental fish, whose natural occurrence is restricted to the Basin of Negro and Orinoco Rivers. It is found mainly in acid and slow flowing water streams, and its reproductive biology is still poorly known. In this work, it is presented information on reproduction and embryonic and larval development in laboratory. The manipulation of the water level (artificial rain), pH and electric conductivity propitiated the spawning of Paracheirodon axelrodi. The species possesses parceled spawning and the eggs are adhesive. Analyses of eight females revealed fecundity values ranging from 154 to 562 oocytes, which were positively related to fish size. The development of the oocytes is of the synchronous type in more than two groups, that is, numberless oocytes in different development phases are liberated in batches. At an average temperature of 26.0 ± 1.0°C, the development of the egg is characterized by a fast embryonic differentiation and a long larval period. The larvae emerged 19-20 hours after fertilization with an average total length of 2.9 ± 0.2 mm and the body was unpigmented. On the fifth day of life, the larvae displayed an average total length of 4.1 ± 0.2 mm and the fins were in development. On the 12th day of life, the first red pigments were observed at the base of the anal fin, and the metallic blue stripe began a slow expansion process to the base of the adipose fin. On the 22nd day of life, all fins were formed, and the young presented an average total length of 11.0 ± 1.0 mm and was very similar to the adult.