96 
THE FISH IN LAKE MAGADI 
The more probable theory of their introduction may be 
taken that some ova adhered to the bills or legs of some of the 
pelicans, flamingoes or duck which frequent the lake. And 
from this start they have increased and multiplied. 
Their habits are briefly as follows : — 
The males appear to be greatly in excess of the females. 
The males may be readily recognised when sexually mature 
by their brighter colouring, iridescence, the white of the 
lower lip more pronounced, absence of vertical barring, and 
usually by their larger size. 
The female is duller in colouring, barred vertically, and when 
gravid considerably swollen, usually fewer in number and 
smaller in size. 
A primitive nest is prepared for the reception of the ova 
in the sandy mud. The work appears to be done entirely 
by the male, but the places prepared appeared to be used by 
many different individuals. 
A male selects a favourable spot, often near a large stone. 
A space of some three inches across is diligently cleaned of 
obstructions, such as the green algae-like growth that coats 
the bottom of the springs, small stones, &c. These are moved 
by the male taking each article in his mouth and depositing 
it on the edges of the depression thus caused. When this is 
finished, one or more females deposit their ova which are later 
fertilized by the male. The process appears to be similar to 
that employed by other fish, the abdomen being pressed against 
the bed of the nest, the fish propelling itself forward at the 
same time. After the operation, other fish appear to deposit 
their ova and milt. Various males appear to keep a cursory 
guard over the nest, driving away other fish in the neighbour- 
hood, but long before the fish are hatched the males’ interest 
in the nest appears to evaporate. The ova are speedily covered 
with the green vegetable deposit and disappear. As soon as the 
fish start to hatch there is a rush of all the neighbouring fish, 
and as many alevins and ova as can be found are devoured by 
the adults. The greater portion of the specimens of alevins 
collected were from the stomachs of fish engaged in thus 
robbing nests. Those that escape the cannibalistic propensities 
of their relatives hide themselves in the algas. On absorption 
