Polyphasic growth in fish: a case study with Corydoras paleatus (Siluriformes, Callichthyidae)

A weight-length relationship was established for Corydoras paleatus(Jenyns, 1842) (Siluriformes, Callichthyidae) (n=596) from samples taken in November-December 2009 and March-April 2010, in Pinguela Lagoon (29°46'57"S; 50°11'16"W), Rio Grande do Sul, Brazil. The species showed a polyphasic allometric growth pattern, each stanzadescribed by an independent power equation controlled by a switch function: W = a1Lb1 ∙ (1 + eRsc ∙ (L-SCP))-1 + a2Lb2 ∙ [1 - (1 + eRsc ∙ (L-SCP))-1] ; where W is the expected weight for a specific length L, a1 and a2 are the proportionality coefficients for stanzas1 and 2, b1 and b2 are the allometric coefficients for stanzas1 and 2, Rsc is the stanzachanging rate for the switch function and SCP is the stanzachanging point for the switch function. The stanzachanging point was estimated as 5.28 cm, corresponding with the length at first maturity for this species Lmat (5.29 cm). Our data suggest that a complex growth pattern can be in nature, and perhaps not often identified because trends are obscured by natural variability.