Ontogenetic allometries and shape changes in the suckermouth armoured catfish <i>Ancistrus</i><i>cf.</i><i>triradiatus</i> Eigenmann (Loricariidae, Siluriformes), related to suckermouth attachment and yolk‐sac size

Abstract

Early life‐history stages of the loricariid catfish Ancistrus cf. triradiatus are described, from pre‐hatch embryos to juveniles. The descriptions, as well as metric characters, indicate that the free‐swimming embryonic stage is followed directly by the juvenile stage, without a true larval stage or metamorphosis. Intense, but gradual ontogenetic head‐shape changes are present during the embryonic and free‐living embryonic stages: the suckermouth gradually shifts from an almost rostral to a ventral position. The external and internal transformations related to this shape change are considered an adaptation to both the loricariid algae‐scraping feeding mode and the need of suckermouth functioning from the moment of hatching, when a ventrally situated suckermouth would be disadvantageous, as a large yolk sac is present.