Abstract
ABSTRACT Headwater creeks are environments susceptible to invasion by non-native fishes. We evaluated the reproduction of 22 populations of the non-native livebearers guppy Poecilia reticulata, black molly Poecilia sphenops, Yucatan molly Poecilia velifera, green swordtail Xiphophorus hellerii, southern platyfish Xiphophorus maculatus, and variable platyfish Xiphophorus variatus during an annual cycle in five headwater creeks located in the largest South American ornamental aquaculture center, Paraíba do Sul River basin, southeastern Brazil. With few exceptions, females of most species were found reproducing (stages 2, 3, 4) all year round in the creeks and gravid females of all species showed small sizes indicating stunting. Juveniles were frequent in all sites. The fecundity of the six poeciliids was always low in all periods. The sex ratio was biased for females in most species, both bimonthly as for the whole period. Water temperature, water level and rainfall were not significantly correlated with reproduction in any species. Therefore, most populations appeared well established. The pertinence of different management actions, such as devices to prevent fish escape, eradication with rotenone and research about negative effects on native species, is discussed in the light of current aquaculture practices in the region.
Highlights
Headwater creeks occur in all landscapes around the globe, and may compose almost 80% of total stream length in many drainage networks (Sidle et al, 2000)
More than 50 non-native fish species are currently found in Brazilian headwater creeks (Bizerril, Lima, 2001; Magalhães, Jacobi, 2008), a group of seven poeciliids deserve special attention as a threat to native communities due to negative impacts such as changes in the structure of the native fish assemblages and biotic homogenization: the guppy Poecilia reticulata Peters, 1859, sailfin molly P. latipinna (Lesueur 1821), black molly P. sphenops Valenciennes in Cuvier, Valenciennes, 1846, Yucatan molly P. velifera (Regan 1914), green swordtail Xiphophorus hellerii Heckel 1848, southern platyfish X. maculatus (Günther 1866), and variable platyfish X. variatus (Meek 1904) (Alves et al, 2007; Magalhães, Jacobi, 2008; Magalhães et al, 2011)
The poeciliids P. reticulata, P. sphenops, X. hellerii and X. maculatus are among the 20 most cultured species, with a combined annual production of almost 3,000,000 individuals raised in monoculture ponds (Cardoso et al, 2012)
Summary
Headwater creeks occur in all landscapes around the globe, and may compose almost 80% of total stream length in many drainage networks (Sidle et al, 2000) They offer an enormous array of habitats for microbial, plant, and animal life, and are sensitive areas for the conservation of aquatic biodiversity due to their low species richness and high degree of endemism (Abell et al, 2007). Cichlids and osphronemids, these poeciliids are the ornamental fishes most sought by the Brazilian aquarium trade (Coe et al, 2011; Magalhães, Jacobi, 2013b; Assis et al, 2014; Garcia et al, 2014) They all have been introduced into headwater creeks of the southeastern region mainly as by-products of aquaculture-related activities (Bizerril, Lima, 2001; Castellani, Barrella, 2006; Alves et al, 2007; Magalhães, Jacobi, 2008). Their members have an invasive advantage over species of other popular non-native families (Milton, Arthington, 1983; Deacon et al, 2011)
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