Major difference in mercury concentrations of the African big barb, Barbus intermedius (R.) due to shifts in trophic position

Abstract

The African big barb (Barbus intermedius, R.) from Lake Awassa, Ethiopia is an important fish species, especially with the ongoing decline of the Nile tilapia (Oreochromis niloticus, L.) fishery. Their diet and habitat use was studied using stomach content analyses, stable nitrogen and carbon isotopes, and transect netting. Mercury biomagnification was also determined. The big barb was found to primarily exist in the littoral habitat, with molluscs being their predominant food item. The proportion of small fish (Barbus paludinosus, P.) in the big barb diet tended to vary somewhat with size, with the largest fish tending to have the most piscivorous diet. Mercury concentrations in the big barb ranged from 0.01 to 0.94 mgAEkg )1 , and were positively related with size. Fish transects and stable isotope analyses suggest that there may be two feeding forms of big barb in Lake Awassa, with some larger fish preying upon fish (and accumulating higher mercury concentrations). With the declining Nile tilapia fishery in Lake Awassa, the implication of fishermen focusing on large big barb, with its associated higher Hg burdens, is significant with human health ramifications.

Mercury Human Exposure in Populations Living Around Lake Tana (Ethiopia)

“…For example, piscivorous big Barbs (Labeobarbus intermedius) in Lake Hawassa has exceeded the marketing limit of the European Union 0.5 mg/kg [7]. It has been reported that Hg concentrations are significantly higher in L. intermedius than in Clarias gariepinus and Oreochromis niloticus in Lake Hawassa [9] and Koka [9,12].…”

Morphometric relationships of African big barb, Labeobarbus intermedius (Rppell, 1836) in Lake Koka, Ethiopia

“…It is present in Ethiopian rift valley basin, Abay basin and Baro-Akobo basin part of Ethiopia, where Lake Tana harbor the largest population (Vijverberg et al, 2012;Awoke, 2015). It is one of the most commercially important fish species in the country (Desta et al, 2006;Bjørklis, 2004). The total annual yield of L. intermedius from the total inland water bodies is estimated to be about 365 tonnes per year (LFDP, 1997).…”

“…Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License overfishing and parasitic infection has resulted in less accessibility of the fish in the local markets (Desta et al, 2006;Mengesha, 2009;Dadebo et al, 2013).…”

Length-Weight Relationship and Condition Factor of African Big Barb <i>Labeobarbus intermedius</i> (Ruppell, 1836) in Ethiopian Freshwater Bodies: A Review

“…It is widely distributed in the rift valley basin, Abay basin and Baro-Akobo basin part of Ethiopia, of which Lake Tana harbors the largest number of big barb species (Vijverberg et al, 2012;Awoke, 2015). It is one of the most commercially important fish species in the country (LFDP4, 1997;Bjørklis, 2004;Desta et al, 2006). The total annual yield of L. intermedius from the total inland water bodies is estimated to be about 365 tons per year (LFDP, 1997).…”

“…However, recently L. intermedius catch from rift valley lakes (Lake Hawassa and Lake Koka) declined and reported to be unsafe for human consumption due to high mercury concentration (Mengesha, 2009). The decline of the fish species due to overfishing and parasitic infection has result the less accessibility of the fish on the local markets (Desta et al, 2006;Mengesha, 2009;Dadebo et al, 2013). Length-weight relationship (LWR) is one of the most important biological tools in fishery management.…”