Early development and allometric growth in the armoured catfish Corydoras aeneus (Gill, 1858)

An ontogenetic series of in-captivity bred Corydoras aeneus was used, in order to study the developmental changes in the external morphology. Allometric growth of several body parts was studied, attempting to reveal important steps in the species' early life history. Based on the external morphology, the different stages during early development of C. aeneus were identified, according to Balon (Journal of the Fisheries Research Board of Canada 32:1663-1670, 1975). After hatching, at a SL of 3.5 mm, the developmental state corresponded to an eleutherembryonic phase, followed by the protopterygiolarval phase (4.4-5.7 mm SL), the pterygiolarval phase (5.7-14.0 mm SL) and the juvenile period. In addition, an overall growth curve and inflexion points were determined. As such, ontogenetic changes in growth coefficients k (in SL = b age k ) were determined. Log transformed data were used for a piecewise linear regression method, as per regression spline smoothing procedures. This way, the growth curve could be divided into six different intervals of growth rate. Initially, the slope was 0.05 until 0.7 dph, then increasing to 0.18 until 4 dph, and 0.36 until 10 dph. After this, growth rate reached a maximum of 0.76 until 24 dph, slowed down to 0.47 until 37 dph and then finally again slowed down to 0.36. A similar growth analysis was also done on the different body parts and these results were compared to both morphological and data from literature. This led to the conclusion that the inflexion points found during the early development of C. aeneus matched the different key-events known in teleost early life history and development. The transition from endo- to exogenous feeding, at the moment a functional branchial respiratory system becomes increasingly important, was the first point at which allometries changed together with functional demands. A second, similar congruence occurred at the transition to the pterygiolarval phase, when priorities shift towards locomotory needs. Finally, our results also indicated a transition to a carangiform swimming mode at approximately 8 mm SL.