Some biological properties of feral swordtail (xiphophorus hellerii) and guppy (poecilia reticulata) populations introduced into thermal springs around tohma stream (euphrates basin)

In this study, the growth and reproductive characteristics of wild Poecilia reticulata (guppy) and Xiphophorus hellerii (green swordtail) populations inhabiting thermal springs located near the Tohma Stream, one of the tributaries of the Euphrates River in the Eastern Anatolia Region, were evaluated. Age determination, length-weight relationship, condition factor (CF₁ and CF₂), gonadosomatic index (GSI), embryo development, and fecundity analyses were performed. A total of 230 Poecilia reticulata and 561 Xiphophorus hellerii individuals were examined in seasonal samplings conducted between February 2024 and February 2025. In Poecilia reticulata individuals, standard length ranged from 11.71 to 35.65 mm and weight ranged from 0.04 to 1.61 g. The condition factor was highest in summer for females (CF₁ = 3.26 ± 0.38) and males (CF₁ = 3.31 ± 0.39). The highest GSI value was recorded in autumn (13.46 ± 5.08), and fecundity ranged between 1 and 39 embryos. In Xiphophorus hellerii individuals, standard length ranged from 13.45 to 58.10 mm and weight ranged from 0.07 to 6.63 g. The condition factor was highest in summer for females (CF₁ = 3.60 ± 0.37) and males (CF₁ = 2.91 ± 0.33). The highest mean GSI was observed in summer (12.61 ± 4.11), and fecundity ranged between 3 and 96 embryos. The dominant age groups in both species were 0+ and 1+ individuals; the presence of 3+ and 4+ age groups in Xiphophorus hellerii indicates that this species is longer-lived. The sex ratio revealed a distribution dominated by females. According to the length-weight relationship calculated for all individuals examined, a significant positive allometric growth was observed in the Poecilia reticulata population, while a negative allometric growth was determined in the Xiphophorus hellerii population.