Habitat use and trophic position determine mercury concentration in the straight fin barb Barbus paludinosus, a small fish species in Lake Awassa, Ethiopia

Abstract

The diet, habitat use and mercury concentration of the small fish species, the straight fin barb Barbus paludinosus, were studied in Lake Awassa, Ethiopia, for a period of 1 year from February 2003 to January 2004. Stable isotope signatures of nitrogen and carbon in different total length (L T ) classes were used to determine trophic positions and organic carbon sources, respectively. Barbus paludinosus mainly occupied the protected benthic habitats (littoral and profundal) of the lake. The d 13 C values were in the range from À24 to À19%, indicating that the carbon source for B. paludinosus was benthic, as well. Small individuals ( 60 mm L T ) mainly preyed upon ostracods, intermediate sizes (60-100 mm) on aquatic insects and gastropods, while a tiny cyprinodont fish Aplocheilichthys antinorii dominated the diet of large individuals (100-160 mm). The progressively increase in d 15 N with increasing L T also indicated a diet shift towards piscivory in larger individuals. The mercury concentration ranging from 0Á02 to 0Á74 mg kg À1 wet mass (wm), was unexpectedly high in this small species, and was significantly positively related to L T , as well as to d 15 N. Some large individuals had mercury concentrations < 0Á1 mg kg À1 wm, and low d 15 N, indicating substantial variations in diet between individuals of same size. The study suggests that other piscivorous species which include B. paludinosus in their diet may have a high mercury intake risk.

The importance of size and growth rate in determining mercury concentrations in European minnow (Phoxinus phoxinus) and brown trout (Salmo trutta) in the subalpine lake, Øvre Heimdalsvatn

“…Stunting in growth of individuals with long lifespan may cause higher mercury levels than in individuals under good growth conditions because of an increasing proportion of mercury per unit body mass (Campbell et al, 2006;Desta et al, 2007a). Growth in length of European minnow and brown trout stagnates at ages of around 5 and 8 years, and at lengths around 8 and 30 cm, respectively, but no marked change in mercury contamination seems to occur in either of the species.…”

Bioaccumulation and Trophic Transfer of Mercury and Selenium in African Sub-Tropical Fluvial Reservoirs Food Webs (Burkina Faso)

“…Several studies from tropical localities have shown that Hg concentration in fish generally increases with both size [ 3 , 54 , 61 ] and trophic position as the result of contaminant accumulation with the exposure time and biomagnification [ 24 , 62 ]. A study carried out in Lake Awassa (Ethiopia) reported the influence of habitat use in the variation of Hg concentration in the piscivorous species Barbus paludinosus [ 63 ] with fish inhabiting the pelagic zone having higher Hg concentration than those preying on benthic organisms. Habitat use is well known in temperate studies to reflect Hg concentration in organisms in lakes with pelagic dwellers having higher concentrations than littoral organisms due to habitat-specific bioaccumulation of MeHg in prey [ 38 , 64 , 65 ].…”

Organochlorine pesticides and heavy metals in fish from Lake Awassa, Ethiopia: Insights from stable isotope analysis

“…These activities as well as population growth have substantially increased the burden of contamination. Recent studies on fish fillets have revealed high levels of mercury (Hg) in Barbus fish species from the lake (Desta et al, 2006(Desta et al, , 2008.…”