Ontogenetic allometries and shape changes in the suckermouth armoured catfish Ancistruscf.triradiatus Eigenmann (Loricariidae, Siluriformes), related to suckermouth attachment and yolk-sac size

Abstract

Early life-history stages of the loricariid catfish Ancistruscf.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.