Pj. Schofield et Lj. Chapman, Hypoxia tolerance of introduced Nile perch: implications for survival of indigenous fishes in the Lake Victoria basin, AFR ZOOL, 35(1), 2000, pp. 35-42
The introduction of predatory Nile perch (Lates niloticus) into the Lake Vi
ctoria basin coincided with a dramatic decline in fish diversity. However,
remnant populations of indigenous fishes persist in lagoons and satellite l
akes separated from the main lakes by extensive areas of swamp, while other
indigenous species find refuge in ecotonal areas at edges of marginal swam
ps in the main lakes. Low-oxygen conditions in these wetlands may physiolog
ically stress Nile perch and therefore minimize its interaction with prey s
pecies. This study examined the low-oxygen tolerance of Nile perch collecte
d from Lake Nabugabo, Uganda, by documenting behavioural and physiological
strategies that relate to oxygen uptake. In response to hypoxia, Nile perch
used aquatic surface respiration (ASR) at the air-water interface, ventila
ting their gills with water from the surface. However, several lines of evi
dence suggest that Nile perch in Lake Nabugabo are inefficient at ASR and r
elatively intolerant of low oxygen conditions. These include high threshold
s for ASR relative to other indigenous fishes of the Lake Victoria basin, n
o decrease in gill ventilation rate with the onset of ASR, a faster time to
loss of equilibrium in hypoxic conditions than other species from the regi
on, and a high critical oxygen tension (24 mm Hg).