Fulton condition factor K of male endler fish (Poecilia wingei) during their growth

Introduction

The Endler's livebearer (Poecilia wingei) is a poeciliid fish native to Venezuela whose wild populations are currently classified as endangered (EN) by the International Union for Conservation of Nature (IUCN) due to their restricted and vulnerable distribution range. In recent years, the species has gained considerable popularity in the ornamental fish trade, particularly males, because of its striking coloration. However, important aspects of its growth and development relevant to conservation and management programs remain poorly understood. Therefore, the present study aimed to evaluate the Fulton condition factor (K) of male Endler's livebearers from birth to sexual maturity.

Methods

A total of 100 newborn fry from five breeding groups were distributed among five 20 L tanks (20 fish per tank) under controlled conditions (pH 7.0, 27.5°C, NH₃ 0 mg L⁻¹, dissolved oxygen 5 mg L⁻¹). Weekly biometric measurements were taken, and Fulton’s condition factor was calculated as K = 100 × weight (g)/ total length³ (mm). Males were separated as gonopodium development became evident and reared under similar conditions until sexual maturity, defined by complete gonopodium formation being reached.

Results

The sex ratio obtained was 1:2 (males), with 33 males recorded. Sexual maturity was reached at 33.25 ± 6.7 days. Fulton’s condition factor decreased from 0.052 ± 0.004 at birth to 0.018 ± 0.0021 at sexual maturity.

Conclusions

Male P. wingei showed a decline in Fulton’s condition factor during sexual maturation, indicating that length increased proportionally faster than weight. These findings contribute to the understanding of the species’ biology and provide valuable information for the development of conservation management strategies and conservation aquaculture programs.