Reproductive biology of Poecilia sphenops Valenciennes, 1846 (Cyprinidontiformes: Poeciliidae) at the Emiliano Zapata Reservoir in Morelos, Mexico

ABSTRACT Poecilia sphenops is a native species recently recorded in the Balsas basin and the Amacuzac River in Morelos (Mexico), in which it is abundant and widely distributed. This study analyzed some aspects of the reproductive biology of Poecilia sphenops from the Emiliano Zapata Reservoir, in Central Mexico. Specimens were collected using a 20 m-long seine with a 5 mm mesh size, from January to December 2006. A total of 581 specimens were collected: 407 females (70.0%), 83 males (14.3%) and 91 individuals with no differentiated sex (15.7%). Fish ranged from 20 to 96 mm in total length and 0.01 to 13.07 g in body weight. The female to male sex ratio (4.9:1) deviated significantly from the unity (χ2= 214.2, p<0.05). Monthly variations in gonadosomatic (GSI) and hepatosomatic (HSI) indexes and ovarian development stages showed that P. sphenops spawning season occurred between July and October, concurring with the rainy season. Another reproduction peak was registered in February. The largest length registered for males and females was 96 mm and 83 mm, respectively.

Reproductive life history of Heterandria bimaculata (Heckel, 1848) (Poeciliinae: Poeciliidae) in the Honduran interior highlands: trait variation along an elevational gradient

Abstract This study examined reproductive traits and growth rates of Heterandria bimaculata (Poeciliidae) in Cusuco National Park (CNP), a cloud forest reserve in northern Honduras, Central America. In CNP, H. bimaculata occurs in the absence of other fish species and major invertebrate predators along an approximately 1000 m elevation gradient. This allowed for the examination of trait variation along the gradient without the confounding effects of interspecific interactions or habitat patchiness. Heterandria bimaculata exhibited traits characteristic of a low-predation environment: balanced sex ratio, slow growth, late maturity and large female size. Females produced more, smaller eggs from upstream to downstream, but overall reproductive allocation remained constant along the gradient. Maximum male length and annual growth rates increased from upstream to downstream, but female growth showed no trend. The patterns of growth and reproductive allocation tradeoff are consistent with predicted response to a longitudinally-increasing productivity gradient in which food resources become more abundant downstream. Macrobrachium and Bellastoma could have caused some predation, but were sparse and patchily distributed. Fish density remained fairly constant among elevations; if food resources were limiting in upstream habitats, per-capita resource availability would be lower and density-dependent competition would drive selection for larger but fewer, more competitive offspring. Future work should quantify longitudinal changes in productivity and conduct experiments to decouple the effects of stream order and fish density dependence.