Allometric growth pattern and morphological changes of the angelfish Pterophyllum scalare (Schultze, 1823) during the early development

Document Type : Regular Paper


1 Department of Fisheries, Faculty of Natural Resources, University of Tehran, Karaj, Iran.

2 Department of Fisheries Sciences, Faculty of Natural Resources, University of Guilan, Sowmeh Sara, P.O. Box 1144, Guilan, Iran


The early development of the angelfish (Pterophyllum scalare) was studied from 1 up to 51 day post hatching under culture conditions. The left side of specimens was photographed and morphometric parameters, including total length, head length, tail length, trunk length, eye diameter, caudal peduncle and body depth were measured using the software ImageJ. Allometric growth pattern was calculated as a power function of total length and the patterns in allometry were described by the growth coefficient to reveal important steps in the species’ early life history. In addition, the anatomical changes were described. The early development of this species was divided into four stages; the eleuthero-embryo, propterygio-larval, pterygio-larval and juvenile. During the first two stages, the growth rate of the head and tail was higher, whereas, in last two stages, the growth rate of the head decreased and the growth rate of the trunk increased, especially at the juvenile stage. This body shape change revealed priorities to develop the organs related to vital functions such as branchial respiration, nervous system and exogenous feeding during preflexion stages (TL=4.52 to 5.54 mm). The growth pattern of the trunk turned to relatively positive allometric growth pattern during the juvenile stages reflected in a deeper body shape along with developed long dorsal and anal fins and higher position of the pectoral fins, an adaptation to its adult life style. The results confirmed this fact that morphological development and growth patterns during early life stages in P. scalare closely match its immediate required function.


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