Emmanuel Frimpong

Despite the global importance of the Nile tilapia Oreochromis niloticus, especially to aquaculture, knowledge of genetic variability within native populations is still limited. While several studies have assessed genetic differentiation across the major drainage basins of Africa, relatively little effort has focused on characterizing genetic differentiation at finer scales. We assessed genetic variation in O. niloticus within and among nine drainage basins in Ghana using nuclear microsatellite DNA markers as the basis for identifying potential units of conservation among wild populations. We screened 312 wild individuals using eight nuclear microsatellite DNA markers. We found moderate genetic diversity within and differentiation among all wild populations studied, with strong signals of recent demographic bottlenecks in several populations. Genetic structure among 11 populations suggested the presence of up to ten management units (MUs). In particular, the Black Volta and the Tano–...

An experiment was carried out to compare the effects of pond fertilization alone, concentrate feeding alone at 5% of fish biomass and a combination of fertilization and feeding at 2.5% of fish biomass on water quality parameters and growth performance and yield of Nile tilapia. The experiment was conducted using nine earthen ponds with average size of 188.67 m2 at Tindiga Village, Kilosa District, Tanzania. The treatments were weekly fertilization alone with urea and Di-Ammonium Phosphate (DAP) at a rate of 3 g/m2 and 2 g/m2, respectively (T1), concentrate feeding alone at 5% of fish biomass (T2) and weekly fertilization with urea and DAP plus concentrate feeding at 2.5% of fish biomass (T3). The concentrate diet contained 30% crude protein. The ponds were stocked with sexreversed Nile tilapia at a stocking density of 3 fingerlings per m2. A random sample of 30 fish per pond was measured for body weight and length every two weeks. Dawn pond water pH, dissolved oxygen (DO), conductiv...

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 predicte...

The development of encompassing general models of ecology is precluded by underrepresentation of certain taxa and systems. Models predicting context‐dependent outcomes of biotic interactions have been tested using plants and bacteria, but their applicability to higher taxa is largely unknown. We examined context dependency in a reproductive mutualism between two stream fish species: mound nest‐building bluehead chub Nocomis leptocephalus and mountain redbelly dace Chrosomus oreas, which often uses N. leptocephalus nests for spawning. We hypothesized that increased predator density and decreased substrate availability would increase the propensity of C. oreas to associate with N. leptocephalus and decrease reproductive success of both species. In a large‐scale in situ experiment, we manipulated egg predator density and presence of both symbionts (biotic context), and replicated the experiment in habitats containing high‐ and low‐quality spawning substrate (abiotic context). Contradic...

Positive interspecific interactions such as mutualism, commensalism, and facilitation are globally ubiquitous. Although research on positive interactions in terrestrial and marine systems has progressed over the past few decades, comparatively little is known about them in freshwater ecosystems. However, recent advances have brought the study of positive interactions in freshwater systems to a point where synthesis is warranted. In this review, we catalogue the variety of direct positive interactions described to date in freshwater ecosystems, discuss factors that could influence prevalence and impact of these interactions, and provide a framework for future research. In positive interactions, organisms exchange key resources such as nutrients, protection, transportation, or habitat to a net benefit for at least one participant. A few mutualistic relationships have received research attention to date, namely seed‐dispersing fishes, crayfishes and their ectosymbiotic cleaners, and co...