Length–Weight Relationships and Body Condition Indices of a South American Bioindicator, the Native Neotropical Fish Species, Cnesterodon decemmaculatus (Poeciliidae)

Abstract

The main goal of our study was to determine the length-weight relationships of Cnesterodon decemmaculatus, as well as to estimate its general fitness through Fulton condition factor (K), relative condition factor (Kn) and the residuals of length–weight relationships. To determine the best index to explain the growth pattern of C. decemmaculatus, a total of 472 adult females were collected from Yuspe River in Córdoba (Argentina), between 2012 and 2019. The length–weight relationships between body weight (W) and standard length (SL) was established by the equation: W = 0.16 × SL3.14, showing a positive allometric growth. Meanwhile, somatic indices presented similar variation patterns, increasing their values during the breeding season (between October and February) since the individuals gain weight due to gonadal maturation and embryonic growth, and decreasing between March and September. We found that K was significantly associated with fishlength, therefore, it would not be appropriate to use it to assess the general body condition of C. decemmaculatus females. According to our results we highly recommend establishing the length–weight relationships first and then selecting the somatic index according to it. We strongly suggest that for future investigation with C. decemmaculatus as a bioindicator, the analyses of residuals of the length–weight relationship is the best method to determine variation patterns of general fish conditions at both field and laboratory studies.