The invasibility of small headwater streams by an emerging invader, Clarias gariepinus

Abstract

African sharptooth catfish Clarias gariepinus has been spread globally and is proven to be invasive with demonstrable impacts on a variety of biota in recipient ecosystems. There are concerns that this species will invade headwater stream communities that are already considered fragile and heavily impacted by non-native invasive fishes. There is however no information on the ability of C. gariepinus to penetrate or establish in these environments. This paper uses data collected over a seven year period from three episodic headwater streams in the Cape Floristic Region of South Africa to assess the ability of C. gariepinus to invade headwater habitats from downstream source populations. Data demonstrate that C. gariepinus invaded all three headwater tributaries and was able to penetrate previously noninvaded threatened fish refugia. Clarias gariepinus however failed to establish in headwaters and their presence was casual with individuals migrating from mainstem sources. Headwater incursions were dynamic and C. gariepinus reinvaded streams following their extirpation through drought. These results indicate headwater streams to be invasible by C. gariepinus and an assessment of potential impact on headwater communities requires urgent attention.

A review of the biology and status of Cape Fold Ecoregion freshwater fishes

“…A study by Kadye and Booth () predicted that the probability of invasion by non‐native African sharptooth catfish Clarias gariepinus decreased from the mainstem Great Fish River to the headwater tributaries. This is in agreement with findings from Ellender, Woodford, and Weyl () who showed that although C. gariepinus did invade headwater tributaries, it was unlikely to become established and invasions were casual and originated from mainstem source populations.…”

A review of Clarias gariepinus invasions in Brazil and South Africa

“…In both South Africa and Brazil, C. gariepinus appear to establish in mainstream and reservoir habitats from where they penetrate into tributary streams where they are contained only by natural (waterfalls) or man‐made (dams) barriers (Alves et al ., ; Vitule et al ., ; Ellender et al ., ). In the Sundays River for example, C. gariepinus were unable to establish in small irrigation ponds (Woodford et al ., ), but use the irrigation network to circumvent barriers and invade headwater stream environments (Ellender et al ., ). Although there is no evidence of establishment in South African headwater streams, the continued presence of C. gariepinus in these streams is facilitated by casual invasions from main stem source populations (Ellender et al ., ).…”

“…In the Sundays River for example, C. gariepinus were unable to establish in small irrigation ponds (Woodford et al ., ), but use the irrigation network to circumvent barriers and invade headwater stream environments (Ellender et al ., ). Although there is no evidence of establishment in South African headwater streams, the continued presence of C. gariepinus in these streams is facilitated by casual invasions from main stem source populations (Ellender et al ., ).…”

“…temperature (8–35° C) and salinities (7–15) (Britz & Hecht, )] and physiological plasticity that is generally greater than that of native species (Gutierre et al ., ) have favoured the escape and subsequent establishment of C. gariepinus in many recipient countries (Alves et al ., ; Orsi & Agostinho, ; Vitule et al ., ; Radhakrishnan et al ., ; Singh & Lakra, ; Ng et al ., ; Singh et al ., ). As a result C. gariepinus is considered an emerging invader (Alexander et al ., ; Ellender et al ., ) and its congener Clarias batrachus (L. 1758) is already listed among the world's worst invasive fishes (Lowe et al ., ). For this reason, the establishment of C. gariepinus in the wild is a cause for concern in many countries (Cambray, ; Vitule et al ., ; Krishnakumar et al ., ; Radhakrishnan et al ., ).…”

An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna

“…In headwater streams in South Africa’s Cape Floristic Region, an area of high freshwater fish and invertebrate biodiversity and endemism [ 22 ], the primary threat to aquatic biota in the region is considered to be predation by and competition with non-native fish species [ 6 , 23 ]. While non-native fish eradication using rotenone is currently considered the most appropriate conservation intervention [ 6 , 24 ], the public as well as the Department of Water Affairs (the South African regulatory authority) have expressed concern on the potential impact of river treatments on non-target organisms (see [ 6 ]).…”