Life‐history pattern of the introduced eastern mosquitofish, Gambusia holbrooki (Baird & Girard, 1854), in a Mediterranean‐type river: The River Guadiana (SW Iberian Peninsula)

Abstract The introduced population of Gambusia holbrooki in the River Guadiana, Iberian Peninsula, was studied for 12 months, focusing on the reproductive ecology. Two main cohorts were identified (2001 and 2002). Females outnumbered males, the average female/male ratio being 1.36. Maximum ages were 2+ in females and 1+ in males. Growth commenced in March and continued until September. Females reached greater sizes, grew faster, and lived longer than males. The largest sizes found were 49.16 mm in females and 31.5 mm in males. Reproducing females were significantly larger in the 2001 cohort (31.10 ± 3.57 SD mm) than in the 2002 one (26.69 ± 4.52 SD mm). Multiple spawning occurred throughout the reproductive cycle (from April to September). The average brood size per female reached its maximum in July in both cohorts (32.95 embryos/female in the 2001 cohort and 30.69 embryos/female in the 2002 one). Potential fecundity was significantly higher than real fecundity in both cohorts. The mean dry weight of int...