Life-history traits of the invasive fish Gambusia holbrooki in saline streams (SE Iberian Peninsula): Does salinity limit its invasive success?

Knowledge of the adaptive ability of the highly invasive fish Gambusia holbrooki to new habitats is essential for determining its invasion potential. Our main objective was to assess the life-history of G. holbrooki in saline streams by studying its abundance, size and age structure, growth and condition. Two populations inhabiting similar streams of different salinity in the southeastern Iberian Peninsula were monitored over a 2 yr period. In both populations, the life-history of the species was characterized by a short life span, a long recruitment period with a massive emergence of young-of-the-year and fast growth of individuals during the first months of their lives. The species showed a less intense recruitment (6.9% of juveniles vs. 46.4% during the recruitment period) and an earlier end of the recruitment period (at least 2 mo) in the hypersaline system, although abundance, hepatic condition and female somatic condition were higher. In addition, temporary increases in salinity diminished population abundance, recruitment, and somatic and hepatic condition. Both populations showed similar seasonal abundance variation patterns, population structures, growth rates, and somatic and hepatic condition cycles. Other environmental factors independent of salinity could have influenced the differentiation in life-history of the species between populations, thus disguising direct relationships between salinity and life-history. However, the studied parameters show that G. holbrooki presents a great ability to adapt to lotic systems with high and different levels of salinity.